Table of Contents
MySQL Cluster is a high-availability, high-redundancy version of
MySQL adapted for the distributed computing environment. It uses the
NDB Cluster
storage engine to enable running
several MySQL servers in a cluster. This storage engine is available
in MySQL 5.0 binary releases and in RPMs compatible
with most modern Linux distributions.
MySQL Cluster is currently available and supported on a number of platforms, including Linux, Solaris, Mac OS X, HP-UX, and other Unix-style operating systems on a variety of hardware. For exact levels of support available for on specific combinations of operating system versions, operating system distributions, and hardware platforms, please refer to the Cluster Supported Platforms list maintained by the MySQL Support Team on the MySQL AB Web site.
MySQL Cluster is not currently supported on Microsoft Windows. We are working to make Cluster available on all operating systems supported by MySQL, including Windows, and will update the information provided here as this work continues.
This chapter represents a work in progress, and its contents are subject to revision as MySQL Cluster continues to evolve. Additional information regarding MySQL Cluster can be found on the MySQL AB Web site at http://www.mysql.com/products/cluster/.
Additional resources. More information may be found in the following places:
Answers to some commonly asked questions about Cluster may be found in the Section A.10, “MySQL 5.0 FAQ — MySQL Cluster”.
The MySQL Cluster mailing list: http://lists.mysql.com/cluster.
The MySQL Cluster Forum: http://forums.mysql.com/list.php?25.
Many MySQL Cluster users and some of the MySQL Cluster developers blog about their experiences with Cluster, and make feeds of these available through PlanetMySQL.
If you are new to MySQL Cluster, you may find our Developer Zone article How to set up a MySQL Cluster for two servers to be helpful.
MySQL Cluster is a technology that enables clustering of in-memory databases in a shared-nothing system. The shared-nothing architecture allows the system to work with very inexpensive hardware, and with a minimum of specific requirements for hardware or software.
MySQL Cluster is designed not to have any single point of failure. For this reason, each component is expected to have its own memory and disk, and the use of shared storage mechanisms such as network shares, network filesystems, and SANs is not recommended or supported.
MySQL Cluster integrates the standard MySQL server with an in-memory
clustered storage engine called NDB
. In our
documentation, the term NDB
refers to the part of
the setup that is specific to the storage engine, whereas
“MySQL Cluster” refers to the combination of MySQL and
the NDB
storage engine.
A MySQL Cluster consists of a set of computers, each running a one or more processes which may include a MySQL server, a data node, a management server, and (possibly) a specialized data access programs. The relationship of these components in a cluster is shown here:
All these programs work together to form a MySQL Cluster. When data
is stored in the NDB Cluster
storage engine, the
tables are stored in the data nodes. Such tables are directly
accessible from all other MySQL servers in the cluster. Thus, in a
payroll application storing data in a cluster, if one application
updates the salary of an employee, all other MySQL servers that
query this data can see this change immediately.
The data stored in the data nodes for MySQL Cluster can be mirrored; the cluster can handle failures of individual data nodes with no other impact than that a small number of transactions are aborted due to losing the transaction state. Because transactional applications are expected to handle transaction failure, this should not be a source of problems.
NDB
is an in-memory
storage engine offering high-availability and data-persistence
features.
The NDB
storage engine can be configured with a
range of failover and load-balancing options, but it is easiest to
start with the storage engine at the cluster level. MySQL
Cluster's NDB
storage engine contains a
complete set of data, dependent only on other data within the
cluster itself.
The cluster portion of MySQL Cluster is currently configured independently of the MySQL servers. In a MySQL Cluster, each part of the cluster is considered to be a node.
In many contexts, the term “node” is used to indicate a computer, but when discussing MySQL Cluster it means a process. It is possible to run any number of nodes on a single computer, for which we use the term cluster host.
(However, it should be noted MySQL does not currently support the use of multiple data nodes on a single computer in a production setting. See Section 16.12.9, “Limitations Relating to Multiple Cluster Nodes”.)
There are three types of cluster nodes, and in a minimal MySQL Cluster configuration, there will be at least three nodes, one of each of these types:
Management node (MGM node): The role of this type of node is to manage the other nodes within the MySQL Cluster, performing such functions as providing configuration data, starting and stopping nodes, running backup, and so forth. Because this node type manages the configuration of the other nodes, a node of this type should be started first, before any other node. An MGM node is started with the command ndb_mgmd.
Data node: This type of node stores cluster data. There are as many data nodes as there are replicas, times the number of fragments. For example, with two replicas, each having two fragments, you will need four data nodes. It is not necessary to have more than one replica. A data node is started with the command ndbd.
SQL node: This is a node that accesses
the cluster data. In the case of MySQL Cluster, an SQL node is
a traditional MySQL server that uses the NDB
Cluster
storage engine. An SQL node is typically
started with the command mysqld
--ndbcluster or by using mysqld
with the ndbcluster
option added to
my.cnf
.
An SQL node is actually just a specialised type of API node, which designates any application which accesses Cluster data. One example of an API node is the ndb_restore utility that is used to restore a cluster backup. It is possible to write such applications using the NDB API.
It is not realistic to expect to employ a three-node setup in a production environment. Such a configuration provides no redundancy; in order to benefit from MySQL Cluster's high-availability features, you must use multiple data and SQL nodes. The use of multiple management nodes is also highly recommended.
For a brief introduction to the relationships between nodes, node groups, replicas, and partitions in MySQL Cluster, see Section 16.1.2, “MySQL Cluster Nodes, Node Groups, Replicas, and Partitions”.
Configuration of a cluster involves configuring each individual node in the cluster and setting up individual communication links between nodes. MySQL Cluster is currently designed with the intention that data nodes are homogeneous in terms of processor power, memory space, and bandwidth. In addition, to provide a single point of configuration, all configuration data for the cluster as a whole is located in one configuration file.
The management server (MGM node) manages the cluster configuration file and the cluster log. Each node in the cluster retrieves the configuration data from the management server, and so requires a way to determine where the management server resides. When interesting events occur in the data nodes, the nodes transfer information about these events to the management server, which then writes the information to the cluster log.
In addition, there can be any number of cluster client processes or applications. These are of two types:
Standard MySQL clients. These are no different for MySQL Cluster than they are for standard (non-Cluster) MySQL. In other words, MySQL Cluster can be accessed from existing MySQL applications written in PHP, Perl, C, C++, Java, Python, Ruby, and so on.
Management clients. These clients connect to the management server and provide commands for starting and stopping nodes gracefully, starting and stopping message tracing (debug versions only), showing node versions and status, starting and stopping backups, and so on.
This section discusses the manner in which MySQL Cluster divides and duplicates data for storage.
Central to an understanding of this topic are the following concepts, listed here with brief definitions:
(Data) Node. An ndbd process, which stores a replica —that is, a copy of the partition (see below) assigned to the node group of which the node is a member.
Each data node should be located on a separate computer. While it is also possible to host multiple ndbd processes on a single computer, such a configuration is not supported.
It is common for the terms “node” and “data node” to be used interchangeably when referring to an ndbd process; where mentioned, management (MGM) nodes (ndb_mgmd processes) and SQL nodes (mysqld processes) are specified as such in this discussion.
Node Group. A node group consists of one or more nodes, and stores partitions, or sets of replicas (see next item).
All node groups in a cluster must have the same number of nodes.
Partition. This is a portion of the data stored by the cluster. There are as many cluster partitions as nodes participating in the cluster. Each node is responsible for keeping at least one copy of any partitions assigned to it (that is, at least one replica) available to the cluster.
A replica belongs entirely to a single node; a node can (and usually does) store several replicas.
Replica. This is a copy of a cluster partition. Each node in a node group stores a replica. Also sometimes known as a partition replica. The number of replicas is equal to the number of nodes per node group.
The following diagram illustrates a MySQL Cluster with four data nodes, arranged in two node groups of two nodes each; nodes 1 and 2 belong to node group 0, and nodes 3 and 4 belong to node group 1. Note that only data (ndbd) nodes are shown here; although a working cluster requires an ndb_mgm process for cluster management and at least one SQL node to access the data stored by the cluster, these have been omitted in the figure for clarity.
The data stored by the cluster is divided into four partitions, numbered 0, 1, 2, and 3. Each partition is stored — in multiple copies — on the same node group. Partitions are stored on alternate node groups:
Partition 0 is stored on node group 0; a primary replica (primary copy) is stored on node 1, and a backup replica (backup copy of the partition) is stored on node 2.
Partition 1 is stored on the other node group (node group 1); this partition's primary replica is on node 3, and its backup replica is on node 4.
Partition 2 is stored on node group 0. However, the placing of its two replicas is reversed from that of Partition 0; for Partition 2, the primary replica is stored on node 2, and the backup on node 1.
Partition 3 is stored on node group 1, and the placement of its two replicas are reversed from those of partition 1. That is, its primary replica is located on node 4, with the backup on node 3.
What this means regarding the continued operation of a MySQL Cluster is this: so long as each node group participating in the cluster has at least one node operating, the cluster has a complete copy of all data and remains viable. This is illustrated in the next diagram.
In this example, where the cluster consists of two node groups of two nodes each, any combination of at least one node in node group 0 and at least one node in node group 1 is sufficient to keep the cluster “alive” (indicated by arrows in the diagram). However, if both nodes from either node group fail, the remaining two nodes are not sufficient (shown by the arrows marked out with an X); in either case, the cluster has lost an entire partition and so can no longer provide access to a complete set of all cluster data.
This section is a “How-To” that describes the basics for how to plan, install, configure, and run a MySQL Cluster. Whereas the examples in Section 16.3, “MySQL Cluster Configuration” provide more in-depth information on a variety of clustering options and configuration, the result of following the guidelines and procedures outlined here should be a usable MySQL Cluster which meets the minimum requirements for availability and safeguarding of data.
This section covers hardware and software requirements; networking issues; installation of MySQL Cluster; configuration issues; starting, stopping, and restarting the cluster; loading of a sample database; and performing queries.
Basic assumptions. This How-To makes the following assumptions:
The cluster setup has four nodes, each on a separate host, and each with a fixed network address on a typical Ethernet as shown here:
Node | IP Address |
Management (MGM) node | 192.168.0.10 |
MySQL server (SQL) node | 192.168.0.20 |
Data (NDBD) node "A" | 192.168.0.30 |
Data (NDBD) node "B" | 192.168.0.40 |
This may be made clearer in the following diagram:
In the interest of simplicity (and reliability), this How-To
uses only numeric IP addresses. However, if DNS resolution is
available on your network, it is possible to use hostnames in
lieu of IP addresses in configuring Cluster. Alternatively, you
can use the /etc/hosts
file or your
operating system's equivalent for providing a means to do host
lookup if such is available.
A common problem when trying to use hostnames for Cluster
nodes arises because of the way in which some operating
systems (including some Linux distributions) set up the
system's own hostname in the /etc/hosts
during installation. Consider two machines with the hostnames
ndb1
and ndb2
, both in
the cluster
network domain. Red Hat Linux
(including some derivatives such as CentOS and Fedora) places
the following entries in these machines'
/etc/hosts
files:
# ndb1 /etc/hosts
:
127.0.0.1 ndb1.cluster ndb1 localhost.localdomain localhost
# ndb2 /etc/hosts
:
127.0.0.1 ndb2.cluster ndb2 localhost.localdomain localhost
SuSE Linux (including OpenSuSE) places these entries in the
machines' /etc/hosts
files:
# ndb1 /etc/hosts
:
127.0.0.1 localhost
127.0.0.2 ndb1.cluster ndb1
# ndb2 /etc/hosts
:
127.0.0.1 localhost
127.0.0.2 ndb2.cluster ndb2
In both instances, ndb1
routes
ndb1.cluster
to a loopback IP address, but
gets a public IP address from DNS for
ndb2.cluster
, while ndb2
routes ndb2.cluster
to a loopback address
and obtains a public address for
ndb1.cluster
. The result is that each data
node connects to the management server, but cannot tell when
any other data nodes have connected, and so the data nodes
appear to hang while starting.
You should also be aware that you cannot mix
localhost
and other hostnames or IP
addresses in config.ini
. For these
reasons, the solution in such cases (other than to use IP
addresses for all
config.ini
HostName
entries) is to remove the fully qualified hostnames from
/etc/hosts
and use these in
config.ini
for all cluster hosts.
Each host in our scenario is an Intel-based desktop PC running a common, generic Linux distribution installed to disk in a standard configuration, and running no unnecessary services. The core OS with standard TCP/IP networking capabilities should be sufficient. Also for the sake of simplicity, we also assume that the filesystems on all hosts are set up identically. In the event that they are not, you will need to adapt these instructions accordingly.
Standard 100 Mbps or 1 gigabit Ethernet cards are installed on each machine, along with the proper drivers for the cards, and that all four hosts are connected via a standard-issue Ethernet networking appliance such as a switch. (All machines should use network cards with the same throughout. That is, all four machines in the cluster should have 100 Mbps cards or all four machines should have 1 Gbps cards.) MySQL Cluster will work in a 100 Mbps network; however, gigabit Ethernet will provide better performance.
Note that MySQL Cluster is not intended for use in a network for which throughput is less than 100 Mbps. For this reason (among others), attempting to run a MySQL Cluster over a public network such as the Internet is not likely to be successful, and is not recommended.
For our sample data, we will use the world
database which is available for download from the MySQL AB Web
site. As this database takes up a relatively small amount of
space, we assume that each machine has 256MB RAM, which should
be sufficient for running the operating system, host NDB
process, and (for the data nodes) for storing the database.
Although we refer to a Linux operating system in this How-To, the instructions and procedures that we provide here should be easily adaptable to other supported operating systems. We also assume that you already know how to perform a minimal installation and configuration of the operating system with networking capability, or that you are able to obtain assistance in this elsewhere if needed.
We discuss MySQL Cluster hardware, software, and networking requirements in somewhat greater detail in the next section. (See Section 16.2.1, “Hardware, Software, and Networking”.)
One of the strengths of MySQL Cluster is that it can be run on commodity hardware and has no unusual requirements in this regard, other than for large amounts of RAM, due to the fact that all live data storage is done in memory. (Note that this is not the case with Disk Data tables, which are implemented in MySQL 5.1; however, we do not intend to backport this feature to MySQL 5.0.) Naturally, multiple and faster CPUs will enhance performance. Memory requirements for other Cluster processes are relatively small.
The software requirements for Cluster are also modest. Host operating systems do not require any unusual modules, services, applications, or configuration to support MySQL Cluster. For supported operating systems, a standard installation should be sufficient. The MySQL software requirements are simple: all that is needed is a production release of MySQL 5.0 to have Cluster support. It is not necessary to compile MySQL yourself merely to be able to use Cluster. In this How-To, we assume that you are using the server binary appropriate to your operating system, available via the MySQL software downloads page at http://dev.mysql.com/downloads/.
For inter-node communication, Cluster supports TCP/IP networking in any standard topology, and the minimum expected for each host is a standard 100 Mbps Ethernet card, plus a switch, hub, or router to provide network connectivity for the cluster as a whole. We strongly recommend that a MySQL Cluster be run on its own subnet which is not shared with non-Cluster machines for the following reasons:
Security. Communications between Cluster nodes are not encrypted or shielded in any way. The only means of protecting transmissions within a MySQL Cluster is to run your Cluster on a protected network. If you intend to use MySQL Cluster for Web applications, the cluster should definitely reside behind your firewall and not in your network's De-Militarized Zone (DMZ) or elsewhere.
See Section 16.8.1, “MySQL Cluster Security and Networking Issues”, for more information.
Efficiency. Setting up a MySQL Cluster on a private or protected network allows the cluster to make exclusive use of bandwidth between cluster hosts. Using a separate switch for your MySQL Cluster not only helps protect against unauthorized access to Cluster data, it also ensures that Cluster nodes are shielded from interference caused by transmissions between other computers on the network. For enhanced reliability, you can use dual switches and dual cards to remove the network as a single point of failure; many device drivers support failover for such communication links.
It is also possible to use the high-speed Scalable Coherent Interface (SCI) with MySQL Cluster, but this is not a requirement. See Section 16.11, “Using High-Speed Interconnects with MySQL Cluster”, for more about this protocol and its use with MySQL Cluster.
Each MySQL Cluster host computer running SQL nodes must have installed on it a MySQL binary. For management nodes and data nodes, it is not necessary to install the MySQL server binary, but management nodes require the management server daemon (ndb_mgmd) and data nodes require the data node daemon (ndbd). It is also a good idea to install the management client (ndb_mgm) on the management server host. This section covers the steps necessary to install the correct binaries for each type of Cluster node.
MySQL AB provides precompiled binaries that support Cluster, and
there is generally no need to compile these yourself. (However, we
also include information relating to installing a MySQL Cluster
after building MySQL from source.) For setting up a cluster using
MySQL's binaries, the first step in the installation process for
each cluster host is to download the file
mysql-5.0.56-pc-linux-gnu-i686.tar.gz
from the MySQL downloads
area. We assume that you have placed it in each machine's
/var/tmp
directory. (If you do require a
custom binary, see Section 2.4.15.3, “Installing from the Development Source Tree”.)
RPMs are also available for both 32-bit and 64-bit Linux platforms. For a MySQL Cluster, three RPMs are required:
The Server RPM (for example,
MySQL-Server-5.0.56-0.glibc23.i386.rpm
),
which supplies the core files needed to run a MySQL Server.
The NDB Cluster - Storage
engine RPM (for example,
MySQL-ndb-storage-5.0.56-0.glibc23.i386.rpm
),
which supplies the MySQL Cluster data node binary
(ndbd).
The NDB Cluster - Storage engine
management RPM (for example,
MySQL-ndb-management-5.0.56-0.glibc23.i386.rpm
),
which provides the MySQL Cluster management server binary
(ndb_mgmd).
In addition, you should also obtain the NDB
Cluster - Storage engine basic tools RPM (for example,
MySQL-ndb-tools-5.0.56-0.glibc23.i386.rpm
),
which supplies several useful applications for working with a
MySQL Cluster. The most important of the these is the MySQL
Cluster management client (ndb_mgm). The
NDB Cluster - Storage engine extra
tools RPM (for example,
MySQL-ndb-extra-5.0.56-0.glibc23.i386.rpm
)
contains some additional testing and monitoring programs, but is
not required to install a MySQL Cluster. (For more information
about these additional programs, see
Section 16.10, “Cluster Utility Programs”.)
The MySQL version number in the RPM filenames (shown here as
5.0.56
) can vary according to the
version which you are actually using. It is very
important that all of the Cluster RPMs to be installed have the
same MySQL version number. The glibc
version number (if present — shown here as
glibc23
), and architecture designation (shown
here as i386
) should be appropriate to the
machine on which the RPM is to be installed.
See Section 2.4.9, “Installing MySQL from RPM Packages on Linux”, for general information about installing MySQL using RPMs supplied by MySQL AB.
After installing from RPM, you still need to configure the cluster as discussed in Section 16.2.3, “Multi-Computer Configuration”.
After completing the installation, do not yet start any of the binaries. We show you how to do so following the configuration of all nodes.
Data and SQL Node Installation — .tar.gz
Binary.
On each of the machines designated to host data or SQL nodes,
perform the following steps as the system
root
user:
Check your /etc/passwd
and
/etc/group
files (or use whatever
tools are provided by your operating system for managing
users and groups) to see whether there is already a
mysql
group and
mysql
user on the system. Some OS
distributions create these as part of the operating system
installation process. If they are not already present,
create a new mysql
user group, and then
add a mysql
user to this group:
shell>groupadd mysql
shell>useradd -g mysql mysql
The syntax for useradd and groupadd may differ slightly on different versions of Unix, or they may have different names such as adduser and addgroup.
Change location to the directory containing the downloaded
file, unpack the archive, and create a symlink to the
mysql
directory named
mysql
. Note that the actual file and
directory names will vary according to the MySQL version
number.
shell>cd /var/tmp
shell>tar -C /usr/local -xzvf mysql-5.0.56-pc-linux-gnu-i686.tar.gz
shell>ln -s /usr/local/mysql-5.0.56-pc-linux-gnu-i686 /usr/local/mysql
Change location to the mysql
directory and run the supplied script for creating the
system databases:
shell>cd mysql
shell>scripts/mysql_install_db --user=mysql
Set the necessary permissions for the MySQL server and data directories:
shell>chown -R root .
shell>chown -R mysql data
shell>chgrp -R mysql .
Note that the data directory on each machine hosting a
data node is /usr/local/mysql/data
.
This piece of information is essential when configuring
the management node. (See
Section 16.2.3, “Multi-Computer Configuration”.)
Copy the MySQL startup script to the appropriate directory, make it executable, and set it to start when the operating system is booted up:
shell>cp support-files/mysql.server /etc/rc.d/init.d/
shell>chmod +x /etc/rc.d/init.d/mysql.server
shell>chkconfig --add mysql.server
(The startup scripts directory may vary depending on your
operating system and version — for example, in some
Linux distributions, it is
/etc/init.d
.)
Here we use Red Hat's chkconfig for creating links to the startup scripts; use whatever means is appropriate for this purpose on your operating system and distribution, such as update-rc.d on Debian.
Remember that the preceding steps must be performed separately on each machine where an SQL node is to reside.
SQL node installation — RPM files. On each machine to be used for hosting a cluster SQL node, install the MySQL Server RPM by executing the following command as the system root user, replacing the name shown for the RPM as necessary to match the name of the RPM downloaded from the MySQL AB web site:
shell> rpm -Uhv MySQL-server-5.0.56-0.glibc23.i386.rpm
This installs the MySQL server binary
(mysqld) in the
/usr/sbin
directory, as well as all needed
MySQL Server support files. It also installs the
mysql.server and
mysqld_safe startup scripts in
/usr/share/mysql
and
/usr/bin
, respectively. The RPM installer
should take care of general configuration issues (such as
creating the mysql
user and group, if needed)
automatically.
SQL node installation — building from source.
If you compile MySQL with clustering support (for example, by
using the
BUILD/compile-platform_name
-max
script appropriate to your platform), and perform the default
installation (using make install as the root
user), mysqld is placed in
/usr/local/mysql/bin
. Follow the steps
given in Section 2.4.15, “MySQL Installation Using a Source Distribution” to make
mysqld ready for use. If you want to run
multiple SQL nodes, you can use a copy of the same
mysqld executable and its associated support
files on several machines. The easiest way to do this is to copy
the entire /usr/local/mysql
directory and
all directories and files contained within it to the other SQL
node host or hosts, then repeat the steps from
Section 2.4.15, “MySQL Installation Using a Source Distribution” on each machine. If you
configure the build with a non-default
--prefix
, you need to adjust the directory
accordingly.
Data node installation — RPM Files. On a computer that is to host a cluster data node it is necessary to install only the NDB Cluster - Storage engine RPM. To do so, copy this RPM to the data node host, and run the following command as the system root user, replacing the name shown for the RPM as necessary to match that of the RPM downloaded from the MySQL AB web site:
shell> rpm -Uhv MySQL-ndb-storage-5.0.56-0.glibc23.i386.rpm
The previous command installs the MySQL Cluster data node binary
(ndbd) in the /usr/sbin
directory.
Data node installation — building from source.
The only executable required on a data node host is
ndbd (mysqld, for example,
does not have to be present on the host machine). By default
when doing a source build, this file is placed in the directory
/usr/local/mysql/libexec
. For installing on
multiple data node hosts, only ndbd need be
copied to the other host machine or machines. (This assumes that
all data node hosts use the same architecture and operating
system; otherwise you may need to compile separately for each
different platform.) ndbd need not be in any
particular location on the host's filesystem, as long as the
location is known.
Management node installation — .tar.gz
binary.
Installation of the management node does not require the
mysqld binary. Only the binary for the
management server is required, which can be found in the
downloaded archive. You most likely want to install the
management client as well; this can also be found in the
.tar.gz
archive. Again, we assume that you
have placed this archive in /var/tmp
.
As system root
(that is, after using
sudo, su root, or your
system's equivalent for temporarily assuming the system
administrator account's privileges), perform the following steps
to install ndb_mgmd and
ndb_mgm on the Cluster management node host:
Change location to the /var/tmp
directory, and extract the ndb_mgm and
ndb_mgmd from the archive into a suitable
directory such as /usr/local/bin
:
shell>cd /var/tmp
shell>tar -zxvf mysql-5.0.56-pc-linux-gnu-i686.tar.gz
shell>cd mysql-5.0.56-pc-linux-gnu-i686
shell>cp /bin/ndb_mgm* /usr/local/bin
(You can safely delete the directory created by unpacking
the downloaded archive, and the files it contains, from
/var/tmp
once
ndb_mgm and ndb_mgmd
have been copied to the executables directory.)
Change location to the directory into which you copied the files, and then make both of them executable:
shell>cd /usr/local/bin
shell>chmod +x ndb_mgm*
Management node installation — RPM file. To install the MySQL Cluster management server, it is necessary only to use the NDB Cluster - Storage engine management RPM. Copy this RPM to the computer intended to host the management node, and then install it by running the following command as the system root user (replace the name shown for the RPM as necessary to match that of the Storage engine management RPM downloaded from the MySQL AB web site):
shell> rpm -Uhv MySQL-ndb-management-5.0.56-0.glibc23.i386.rpm
This installs the management server binary
(ndb_mgmd) to the
/usr/sbin
directory.
You should also install the NDB
management
client, which is supplied by the Storage
engine basic tools RPM. Copy this RPM to the same
computer as the management node, and then install it by running
the following command as the system root user (again, replace the
name shown for the RPM as necessary to match that of the
Storage engine basic tools RPM
downloaded from the MySQL AB web site):
shell> rpm -Uhv MySQL-ndb-tools-5.0.56-0.glibc23.i386.rpm
The Storage engine basic tools
RPM installs the MySQL Cluster management client
(ndb_mgm) to the /usr/bin
directory.
Management node installation — building from source.
When building from source and running the default make
install, the management server binary
(ndb_mgmd) is placed in
/usr/local/mysql/libexec
, while the
management client binary (ndb_mgm) can be
found in /usr/local/mysql/bin
. Only
ndb_mgmd is required to be present on a
management node host; however, it is also a good idea to have
ndb_mgm present on the same host machine.
Neither of these executables requires a specific location on the
host machine's filesystem.
In Section 16.2.3, “Multi-Computer Configuration”, we create configuration files for all of the nodes in our example Cluster.
For our four-node, four-host MySQL Cluster, it is necessary to write four configuration files, one per node host.
Each data node or SQL node requires a
my.cnf
file that provides two pieces of
information: a connectstring that tells
the node where to find the MGM node, and a line telling the
MySQL server on this host (the machine hosting the data node)
to run in NDB mode.
For more information on connectstrings, see Section 16.3.4.2, “The Cluster Connectstring”.
The management node needs a config.ini
file telling it how many replicas to maintain, how much memory
to allocate for data and indexes on each data node, where to
find the data nodes, where to save data to disk on each data
node, and where to find any SQL nodes.
Configuring the Storage and SQL Nodes
The my.cnf
file needed for the data nodes is
fairly simple. The configuration file should be located in the
/etc
directory and can be edited using any
text editor. (Create the file if it does not exist.) For example:
shell> vi /etc/my.cnf
We show vi being used here to create the file, but any text editor should work just as well.
For each data node and SQL node in our example setup,
my.cnf
should look like this:
# Options for mysqld process: [mysqld] ndbcluster # run NDB storage engine ndb-connectstring=192.168.0.10 # location of management server # Options for ndbd process: [mysql_cluster] ndb-connectstring=192.168.0.10 # location of management server
After entering the preceding information, save this file and exit the text editor. Do this for the machines hosting data node “A”, data node “B”, and the SQL node.
Once you have started a mysqld process with
the ndbcluster
and
ndb-connectstring
parameters in the
[mysqld]
in the my.cnf
file as shown previously, you cannot execute any CREATE
TABLE
or ALTER TABLE
statements
without having actually started the cluster. Otherwise, these
statements will fail with an error. This is by
design.
Configuring the management node.
The first step in configuring the MGM node is to create the
directory in which the configuration file can be found and then
to create the file itself. For example (running as
root
):
shell>mkdir /var/lib/mysql-cluster
shell>cd /var/lib/mysql-cluster
shell>vi config.ini
For our representative setup, the config.ini
file should read as follows:
# Options affecting ndbd processes on all data nodes: [ndbd default] NoOfReplicas=2 # Number of replicas DataMemory=80M # How much memory to allocate for data storage IndexMemory=18M # How much memory to allocate for index storage # For DataMemory and IndexMemory, we have used the # default values. Since the "world" database takes up # only about 500KB, this should be more than enough for # this example Cluster setup. # TCP/IP options: [tcp default] portnumber=2202 # This the default; however, you can use any # port that is free for all the hosts in cluster # Note: It is recommended beginning with MySQL 5.0 that # you do not specify the portnumber at all and simply allow # the default value to be used instead # Management process options: [ndb_mgmd] hostname=192.168.0.10 # Hostname or IP address of MGM node datadir=/var/lib/mysql-cluster # Directory for MGM node log files # Options for data node "A": [ndbd] # (one [ndbd] section per data node) hostname=192.168.0.30 # Hostname or IP address datadir=/usr/local/mysql/data # Directory for this data node's data files # Options for data node "B": [ndbd] hostname=192.168.0.40 # Hostname or IP address datadir=/usr/local/mysql/data # Directory for this data node's data files # SQL node options: [mysqld] hostname=192.168.0.20 # Hostname or IP address # (additional mysqld connections can be # specified for this node for various # purposes such as running ndb_restore)
The world
database can be downloaded from
http://dev.mysql.com/doc/, where it can be found listed
under “Examples”.
After all the configuration files have been created and these minimal options have been specified, you are ready to proceed with starting the cluster and verifying that all processes are running. We discuss how this is done in Section 16.2.4, “Initial Startup”.
For more detailed information about the available MySQL Cluster configuration parameters and their uses, see Section 16.3.4, “Configuration File”, and Section 16.3, “MySQL Cluster Configuration”. For configuration of MySQL Cluster as relates to making backups, see Section 16.9.4, “Configuration for Cluster Backup”.
The default port for Cluster management nodes is 1186; the default port for data nodes is 2202. Beginning with MySQL 5.0.3, this restriction is lifted, and the cluster automatically allocates ports for data nodes from those that are already free.
Starting the cluster is not very difficult after it has been configured. Each cluster node process must be started separately, and on the host where it resides. The management node should be started first, followed by the data nodes, and then finally by any SQL nodes:
On the management host, issue the following command from the system shell to start the management node process:
shell> ndb_mgmd -f /var/lib/mysql-cluster/config.ini
Note that ndb_mgmd must be told where to
find its configuration file, using the -f
or
--config-file
option. (See
Section 16.6.3, “ndb_mgmd — The Management Server Process”, for
details.)
On each of the data node hosts, run this command to start the ndbd process:
shell> ndbd
If you used RPM files to install MySQL on the cluster host where the SQL node is to reside, you can (and should) use the supplied startup script to start the MySQL server process on the SQL node.
If all has gone well, and the cluster has been set up correctly, the cluster should now be operational. You can test this by invoking the ndb_mgm management node client. The output should look like that shown here, although you might see some slight differences in the output depending upon the exact version of MySQL that you are using:
shell>ndb_mgm
-- NDB Cluster -- Management Client -- ndb_mgm>SHOW
Connected to Management Server at: localhost:1186 Cluster Configuration --------------------- [ndbd(NDB)] 2 node(s) id=2 @192.168.0.30 (Version: 5.0.56, Nodegroup: 0, Master) id=3 @192.168.0.40 (Version: 5.0.56, Nodegroup: 0) [ndb_mgmd(MGM)] 1 node(s) id=1 @192.168.0.10 (Version: 5.0.56) [mysqld(SQL)] 1 node(s) id=4 (Version: 5.0.56)
The SQL node is referenced here as
[mysqld(API)]
. This is perfectly normal, and
reflects the fact that the mysqld process is
acting as a cluster API node.
You should now be ready to work with databases, tables, and data in MySQL Cluster. See Section 16.2.5, “Loading Sample Data and Performing Queries”, for a brief discussion.
Working with data in MySQL Cluster is not much different from doing so in MySQL without Cluster. There are two points to keep in mind:
For a table to be replicated in the cluster, it must use the
NDB Cluster
storage engine. To specify
this, use the ENGINE=NDB
or
ENGINE=NDBCLUSTER
table option. You can add
this option when creating the table:
CREATE TABLEtbl_name
(col_name
column_definitions
) ENGINE=NDBCLUSTER;
Alternatively, for an existing table that uses a different
storage engine, use ALTER TABLE
to change
the table to use NDB Cluster
:
ALTER TABLE tbl_name
ENGINE=NDBCLUSTER;
Each NDB
table must
have a primary key. If no primary key is defined by the user
when a table is created, the NDB Cluster
storage engine automatically generates a hidden one.
This hidden key takes up space just as does any other table index. It is not uncommon to encounter problems due to insufficient memory for accommodating these automatically created indexes.)
If you are importing tables from an existing database using the
output of mysqldump, you can open the SQL
script in a text editor and add the ENGINE
option to any table creation statements, or replace any existing
ENGINE
(or TYPE
) options.
Suppose that you have the world
sample database
on another MySQL server that does not support MySQL Cluster, and
you want to export the City
table:
shell> mysqldump --add-drop-table world City > city_table.sql
The resulting city_table.sql
file will
contain this table creation statement (and the
INSERT
statements necessary to import the table
data):
DROP TABLE IF EXISTS `City`;
CREATE TABLE `City` (
`ID` int(11) NOT NULL auto_increment,
`Name` char(35) NOT NULL default '',
`CountryCode` char(3) NOT NULL default '',
`District` char(20) NOT NULL default '',
`Population` int(11) NOT NULL default '0',
PRIMARY KEY (`ID`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1;
INSERT INTO `City` VALUES (1,'Kabul','AFG','Kabol',1780000);
INSERT INTO `City` VALUES (2,'Qandahar','AFG','Qandahar',237500);
INSERT INTO `City` VALUES (3,'Herat','AFG','Herat',186800);
(remaining INSERT statements omitted)
You need to make sure that MySQL uses the NDB
storage engine for this table. There are two ways that this can be
accomplished. One of these is to modify the table definition
before importing it into the Cluster
database. Using the City
table as an example,
modify the ENGINE
option of the definition as
follows:
DROP TABLE IF EXISTS `City`;
CREATE TABLE `City` (
`ID` int(11) NOT NULL auto_increment,
`Name` char(35) NOT NULL default '',
`CountryCode` char(3) NOT NULL default '',
`District` char(20) NOT NULL default '',
`Population` int(11) NOT NULL default '0',
PRIMARY KEY (`ID`)
) ENGINE=NDBCLUSTER DEFAULT CHARSET=latin1;
INSERT INTO `City` VALUES (1,'Kabul','AFG','Kabol',1780000);
INSERT INTO `City` VALUES (2,'Qandahar','AFG','Qandahar',237500);
INSERT INTO `City` VALUES (3,'Herat','AFG','Herat',186800);
(remaining INSERT statements omitted)
This must be done for the definition of each table that is to be
part of the clustered database. The easiest way to accomplish this
is to do a search-and-replace on the file that contains the
definitions and replace all instances of
TYPE=
or
engine_name
ENGINE=
with engine_name
ENGINE=NDBCLUSTER
. If you do not want to
modify the file, you can use the unmodified file to create the
tables, and then use ALTER TABLE
to change
their storage engine. The particulars are given later in this
section.
Assuming that you have already created a database named
world
on the SQL node of the cluster, you can
then use the mysql command-line client to read
city_table.sql
, and create and populate the
corresponding table in the usual manner:
shell> mysql world < city_table.sql
It is very important to keep in mind that the preceding command
must be executed on the host where the SQL node is running (in
this case, on the machine with the IP address
192.168.0.20
).
To create a copy of the entire world
database
on the SQL node, use mysqldump on the
non-cluster server to export the database to a file named
world.sql
; for example, in the
/tmp
directory. Then modify the table
definitions as just described and import the file into the SQL
node of the cluster like this:
shell> mysql world < /tmp/world.sql
If you save the file to a different location, adjust the preceding instructions accordingly.
It is important to note that NDB Cluster
in
MySQL 5.0 does not support autodiscovery of
databases. (See Section 16.12, “Known Limitations of MySQL Cluster”.) This
means that, once the world
database and its
tables have been created on one data node, you need to issue the
CREATE DATABASE world
statement (beginning with
MySQL 5.0.2, you may use CREATE SCHEMA world
instead), followed by FLUSH TABLES
on each SQL
node in the cluster. This causes the node to recognize the
database and read its table definitions.
Running SELECT
queries on the SQL node is no
different from running them on any other instance of a MySQL
server. To run queries from the command line, you first need to
log in to the MySQL Monitor in the usual way (specify the
root
password at the Enter
password:
prompt):
shell> mysql -u root -p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 1 to server version: 5.0.56
Type 'help;' or '\h' for help. Type '\c' to clear the buffer.
mysql>
We simply use the MySQL server's root
account
and assume that you have followed the standard security
precautions for installing a MySQL server, including setting a
strong root
password. For more information, see
Section 2.4.16.3, “Securing the Initial MySQL Accounts”.
It is worth taking into account that Cluster nodes do
not make use of the MySQL privilege system
when accessing one another. Setting or changing MySQL user
accounts (including the root
account) effects
only applications that access the SQL node, not interaction
between nodes. See
Section 16.8.2, “MySQL Cluster and MySQL Privileges”, for
more information.
If you did not modify the ENGINE
clauses in the
table definitions prior to importing the SQL script, you should
run the following statements at this point:
mysql>USE world;
mysql>ALTER TABLE City ENGINE=NDBCLUSTER;
mysql>ALTER TABLE Country ENGINE=NDBCLUSTER;
mysql>ALTER TABLE CountryLanguage ENGINE=NDBCLUSTER;
Selecting a database and running a SELECT query against a table in that database is also accomplished in the usual manner, as is exiting the MySQL Monitor:
mysql>USE world;
mysql>SELECT Name, Population FROM City ORDER BY Population DESC LIMIT 5;
+-----------+------------+ | Name | Population | +-----------+------------+ | Bombay | 10500000 | | Seoul | 9981619 | | São Paulo | 9968485 | | Shanghai | 9696300 | | Jakarta | 9604900 | +-----------+------------+ 5 rows in set (0.34 sec) mysql>\q
Bye shell>
Applications that use MySQL can employ standard APIs to access
NDB
tables. It is important to remember that
your application must access the SQL node, and not the management
or data nodes. This brief example shows how we might execute the
SELECT
statement just shown by using the PHP
5.X mysqli
extension running on a Web server
elsewhere on the network:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type"
content="text/html; charset=iso-8859-1">
<title>SIMPLE mysqli SELECT</title>
</head>
<body>
<?php
# connect to SQL node:
$link = new mysqli('192.168.0.20', 'root', 'root_password
', 'world');
# parameters for mysqli constructor are:
# host, user, password, database
if( mysqli_connect_errno() )
die("Connect failed: " . mysqli_connect_error());
$query = "SELECT Name, Population
FROM City
ORDER BY Population DESC
LIMIT 5";
# if no errors...
if( $result = $link->query($query) )
{
?>
<table border="1" width="40%" cellpadding="4" cellspacing ="1">
<tbody>
<tr>
<th width="10%">City</th>
<th>Population</th>
</tr>
<?
# then display the results...
while($row = $result->fetch_object())
printf(<tr>\n <td align=\"center\">%s</td><td>%d</td>\n</tr>\n",
$row->Name, $row->Population);
?>
</tbody
</table>
<?
# ...and verify the number of rows that were retrieved
printf("<p>Affected rows: %d</p>\n", $link->affected_rows);
}
else
# otherwise, tell us what went wrong
echo mysqli_error();
# free the result set and the mysqli connection object
$result->close();
$link->close();
?>
</body>
</html>
We assume that the process running on the Web server can reach the IP address of the SQL node.
In a similar fashion, you can use the MySQL C API, Perl-DBI, Python-mysql, or MySQL AB's own Connectors to perform the tasks of data definition and manipulation just as you would normally with MySQL.
To shut down the cluster, enter the following command in a shell on the machine hosting the management node:
shell> ndb_mgm -e shutdown
The -e
option here is used to pass a command to
the ndb_mgm client from the shell. See
Section 4.2.2.1, “Using Options on the Command Line”. The command causes the
ndb_mgm, ndb_mgmd, and any
ndbd processes to terminate gracefully. Any SQL
nodes can be terminated using mysqladmin
shutdown and other means.
To restart the cluster, run these commands:
On the management host (192.168.0.10
in our
example setup):
shell> ndb_mgmd -f /var/lib/mysql-cluster/config.ini
On each of the data node hosts
(192.168.0.30
and
192.168.0.40
):
shell> ndbd
On the SQL host (192.168.0.20
):
shell> mysqld_safe &
For information on making Cluster backups, see Section 16.9.2, “Using The Management Client to Create a Backup”.
To restore the cluster from backup requires the use of the ndb_restore command. This is covered in Section 16.9.3, “ndb_restore — Restore a Cluster Backup”.
More information on configuring MySQL Cluster can be found in Section 16.3, “MySQL Cluster Configuration”.
A MySQL server that is part of a MySQL Cluster differs in only one
respect from a normal (non-clustered) MySQL server, in that it
employs the NDB Cluster
storage engine. This
engine is also referred to simply as NDB
, and the
two forms of the name are synonymous.
To avoid unnecessary allocation of resources, the server is
configured by default with the NDB
storage engine
disabled. To enable NDB
, you must modify the
server's my.cnf
configuration file, or start
the server with the --ndbcluster
option.
For more information about --ndbcluster
and other
MySQL server options specific to MySQL Cluster, see
Section 16.4.2, “MySQL Cluster-Related Command Options for mysqld”.
The MySQL server is a part of the cluster, so it also must know how
to access an MGM node to obtain the cluster configuration data. The
default behavior is to look for the MGM node on
localhost
. However, should you need to specify
that its location is elsewhere, this can be done in
my.cnf
or on the MySQL server command line.
Before the NDB
storage engine can be used, at
least one MGM node must be operational, as well as any desired data
nodes.
NDB
, the Cluster storage engine, is available
in binary distributions for Linux, Mac OS X, and Solaris. We are
working to make Cluster run on all operating systems supported by
MySQL, including Windows.
If you choose to build from a source tarball or the MySQL
5.0 BitKeeper tree, be sure to use the
--with-ndbcluster
option when running
configure. You can also use the
BUILD/compile-pentium-max build script. Note
that this script includes OpenSSL, so you must either have or
obtain OpenSSL to build successfully, or else modify
compile-pentium-max to exclude this
requirement. Of course, you can also just follow the standard
instructions for compiling your own binaries, and then perform the
usual tests and installation procedure. See
Section 2.4.15.3, “Installing from the Development Source Tree”.
You should also note that compile-pentium-max
installs MySQL to the directory
/usr/local/mysql
, placing all MySQL Cluster
executables, scripts, databases, and support files in
subdirectories under this directory. If this is not what you
desire, be sure to modify the script accordingly.
In the next few sections, we assume that you are already familiar with installing MySQL, and here we cover only the differences between configuring MySQL Cluster and configuring MySQL without clustering. (See Chapter 2, Installing and Upgrading MySQL, if you require more information about the latter.)
You will find Cluster configuration easiest if you have already
have all management and data nodes running first; this is likely
to be the most time-consuming part of the configuration. Editing
the my.cnf
file is fairly straightforward,
and this section will cover only any differences from configuring
MySQL without clustering.
To familiarize you with the basics, we will describe the simplest possible configuration for a functional MySQL Cluster. After this, you should be able to design your desired setup from the information provided in the other relevant sections of this chapter.
First, you need to create a configuration directory such as
/var/lib/mysql-cluster
, by executing the
following command as the system root
user:
shell> mkdir /var/lib/mysql-cluster
In this directory, create a file named
config.ini
that contains the following
information. Substitute appropriate values for
HostName
and DataDir
as
necessary for your system.
# file "config.ini" - showing minimal setup consisting of 1 data node, # 1 management server, and 3 MySQL servers. # The empty default sections are not required, and are shown only for # the sake of completeness. # Data nodes must provide a hostname but MySQL Servers are not required # to do so. # If you don't know the hostname for your machine, use localhost. # The DataDir parameter also has a default value, but it is recommended to # set it explicitly. # Note: [db], [api], and [mgm] are aliases for [ndbd], [mysqld], and [ndb_mgmd], # respectively. [db] is deprecated and should not be used in new installations. [ndbd default] NoOfReplicas= 1 [mysqld default] [ndb_mgmd default] [tcp default] [ndb_mgmd] HostName= myhost.example.com [ndbd] HostName= myhost.example.com DataDir= /var/lib/mysql-cluster [mysqld] [mysqld] [mysqld]
You can now start the ndb_mgmd management
server. By default, it attempts to read the
config.ini
file in its current working
directory, so change location into the directory where the file is
located and then invoke ndb_mgmd:
shell>cd /var/lib/mysql-cluster
shell>ndb_mgmd
Then start a single data node by running ndbd:
shell> ndbd
By default, ndbd looks for the management
server at localhost
on port 1186.
If you have installed MySQL from a binary tarball, you will need
to specify the path of the ndb_mgmd and
ndbd servers explicitly. (Normally, these
will be found in /usr/local/mysql/bin
.)
Finally, change location to the MySQL data directory (usually
/var/lib/mysql
or
/usr/local/mysql/data
), and make sure that
the my.cnf
file contains the option necessary
to enable the NDB storage engine:
[mysqld] ndbcluster
You can now start the MySQL server as usual:
shell> mysqld_safe --user=mysql &
Wait a moment to make sure the MySQL server is running properly.
If you see the notice mysql ended
, check the
server's .err
file to find out what went
wrong.
If all has gone well so far, you now can start using the cluster.
Connect to the server and verify that the
NDBCLUSTER
storage engine is enabled:
shell>mysql
Welcome to the MySQL monitor. Commands end with ; or \g. Your MySQL connection id is 1 to server version: 5.0.56 Type 'help;' or '\h' for help. Type '\c' to clear the buffer. mysql>SHOW ENGINES\G
... *************************** 12. row *************************** Engine: NDBCLUSTER Support: YES Comment: Clustered, fault-tolerant, memory-based tables *************************** 13. row *************************** Engine: NDB Support: YES Comment: Alias for NDBCLUSTER ...
The row numbers shown in the preceding example output may be different from those shown on your system, depending upon how your server is configured.
Try to create an NDBCLUSTER
table:
shell>mysql
mysql>USE test;
Database changed mysql>CREATE TABLE ctest (i INT) ENGINE=NDBCLUSTER;
Query OK, 0 rows affected (0.09 sec) mysql>SHOW CREATE TABLE ctest \G
*************************** 1. row *************************** Table: ctest Create Table: CREATE TABLE `ctest` ( `i` int(11) default NULL ) ENGINE=ndbcluster DEFAULT CHARSET=latin1 1 row in set (0.00 sec)
To check that your nodes were set up properly, start the management client:
shell> ndb_mgm
Use the SHOW command from within the management client to obtain a report on the cluster's status:
ndb_mgm> SHOW
Cluster Configuration
---------------------
[ndbd(NDB)] 1 node(s)
id=2 @127.0.0.1 (Version: 3.5.3, Nodegroup: 0, Master)
[ndb_mgmd(MGM)] 1 node(s)
id=1 @127.0.0.1 (Version: 3.5.3)
[mysqld(API)] 3 node(s)
id=3 @127.0.0.1 (Version: 3.5.3)
id=4 (not connected, accepting connect from any host)
id=5 (not connected, accepting connect from any host)
At this point, you have successfully set up a working MySQL
Cluster. You can now store data in the cluster by using any table
created with ENGINE=NDBCLUSTER
or its alias
ENGINE=NDB
.
Configuring MySQL Cluster requires working with two files:
my.cnf
: Specifies options for all MySQL
Cluster executables. This file, with which you should be
familiar with from previous work with MySQL, must be
accessible by each executable running in the cluster.
config.ini
: This file is read only by the
MySQL Cluster management server, which then distributes the
information contained therein to all processes participating
in the cluster. config.ini
contains a
description of each node involved in the cluster. This
includes configuration parameters for data nodes and
configuration parameters for connections between all nodes in
the cluster. For a quick reference to the sections that can
appear in this file, and what sorts of configuration
parameters may be placed in each section, see
Sections of
the config.ini
File.
We are continuously making improvements in Cluster configuration and attempting to simplify this process. Although we strive to maintain backward compatibility, there may be times when introduce an incompatible change. In such cases we will try to let Cluster users know in advance if a change is not backward compatible. If you find such a change and we have not documented it, please report it in the MySQL bugs database using the instructions given in Section 1.7, “How to Report Bugs or Problems”.
To support MySQL Cluster, you will need to update
my.cnf
as shown in the following example.
Note that the options shown here should not be confused with
those that are used in config.ini
files.
You may also specify these parameters on the command line when
invoking the executables.
# my.cnf # example additions to my.cnf for MySQL Cluster # (valid in MySQL 5.0) # enable ndbcluster storage engine, and provide connectstring for # management server host (default port is 1186) [mysqld] ndbcluster ndb-connectstring=ndb_mgmd.mysql.com # provide connectstring for management server host (default port: 1186) [ndbd] connect-string=ndb_mgmd.mysql.com # provide connectstring for management server host (default port: 1186) [ndb_mgm] connect-string=ndb_mgmd.mysql.com # provide location of cluster configuration file [ndb_mgmd] config-file=/etc/config.ini
(For more information on connectstrings, see Section 16.3.4.2, “The Cluster Connectstring”.)
# my.cnf # example additions to my.cnf for MySQL Cluster # (will work on all versions) # enable ndbcluster storage engine, and provide connectstring for management # server host to the default port 1186 [mysqld] ndbcluster ndb-connectstring=ndb_mgmd.mysql.com:1186
Once you have started a mysqld process with
the ndbcluster
and
ndb-connectstring
parameters in the
[mysqld]
in the my.cnf
file as shown previously, you cannot execute any
CREATE TABLE
or ALTER
TABLE
statements without having actually started the
cluster. Otherwise, these statements will fail with an error.
This is by design.
You may also use a separate [mysql_cluster]
section in the cluster my.cnf
file for
settings to be read and used by all executables:
# cluster-specific settings [mysql_cluster] ndb-connectstring=ndb_mgmd.mysql.com:1186
For additional NDB
variables that can be set
in the my.cnf
file, see
Section 5.1.3, “System Variables”.
The configuration file is named config.ini
by default. It is read by ndb_mgmd at startup
and can be placed anywhere. Its location and name are specified
by using
--config-file=
on the ndb_mgmd command line. If the
configuration file is not specified, ndb_mgmd
by default tries to read a file named
path_name
config.ini
located in the current working
directory.
Currently, the configuration file is in INI format, which
consists of sections preceded by section headings (surrounded by
square brackets), followed by the appropriate parameter names
and values. One deviation from the standard INI format is that
the parameter name and value can be separated by a colon
(“:
”) as well as the equals sign
(“=
”); however, the equals sign
is preferred. Another deviation is that sections are not
uniquely identified by section name. Instead, unique sections
(such as two different nodes of the same type) are identified by
a unique ID specified as a parameter within the section.
Default values are defined for most parameters, and can also be
specified in config.ini
. To create a
default value section, simply add the word
default
to the section name. For example, an
[ndbd]
section contains parameters that apply
to a particular data node, whereas an [ndbd
default]
section contains parameters that apply to all
data nodes. Suppose that all data nodes should use the same data
memory size. To configure them all, create an [ndbd
default]
section that contains a
DataMemory
line to specify the data memory
size.
At a minimum, the configuration file must define the computers and nodes involved in the cluster and on which computers these nodes are located. An example of a simple configuration file for a cluster consisting of one management server, two data nodes and two MySQL servers is shown here:
# file "config.ini" - 2 data nodes and 2 SQL nodes # This file is placed in the startup directory of ndb_mgmd (the # management server) # The first MySQL Server can be started from any host. The second # can be started only on the host mysqld_5.mysql.com [ndbd default] NoOfReplicas= 2 DataDir= /var/lib/mysql-cluster [ndb_mgmd] Hostname= ndb_mgmd.mysql.com DataDir= /var/lib/mysql-cluster [ndbd] HostName= ndbd_2.mysql.com [ndbd] HostName= ndbd_3.mysql.com [mysqld] [mysqld] HostName= mysqld_5.mysql.com
Each node has its own section in the
config.ini
file. For example, this cluster
has two data nodes, so the preceding configuration file contains
two [ndbd]
sections defining these nodes.
Do not place comments on the same line as a section heading in
the config.ini
file; this causes the
management server not to start because it cannot parse the
configuration file in such cases.
Sections of the
config.ini
File
There are six different sections that you can use in the
config.ini
configuration file, as described
in the following list:
[computer]
: Defines cluster hosts. This
is not required to configure a viable MySQL Cluster, but be
may used as a convenience when setting up a large cluster.
See Section 16.3.4.3, “Defining Cluster Computers”, for
more information.
[ndbd]
: Defines a cluster data node
(ndbd process). See
Section 16.3.4.5, “Defining Data Nodes”, for
details.
[mysqld]
: Defines the cluster's MySQL
server nodes (also called SQL or API nodes). For a
discussion of SQL node configuration, see
Section 16.3.4.6, “Defining SQL and Other API Nodes”.
[mgm]
or [ndb_mgmd]
:
Defines a cluster management server (MGM) node. For
information concerning the configuration of MGM nodes, see
Section 16.3.4.4, “Defining the Management Server”.
[tcp]
: Defines a TCP/IP connection
between cluster nodes, with TCP/IP being the default
connection protocol. Normally, [tcp]
or
[tcp default]
sections are not required
to set up a MySQL Cluster, as the cluster handles this
automatically; however, it may be necessary in some
situations to override the defaults provided by the cluster.
See Section 16.3.4.7, “Cluster TCP/IP Connections”, for
information about available TCP/IP configuration parameters
and how to use them. (You may also find
Section 16.3.4.8, “TCP/IP Connections Using Direct Connections” to be
of interest in some cases.)
[shm]
: Defines shared-memory connections
between nodes. In MySQL 5.0, it is enabled by
default, but should still be considered experimental. For a
discussion of SHM interconnects, see
Section 16.3.4.9, “Shared-Memory Connections”.
[sci]
:Defines Scalable
Coherent Interface connections between cluster
data nodes. Such connections require software which, while
freely available, is not part of the MySQL Cluster
distribution, as well as specialised hardware. See
Section 16.3.4.10, “SCI Transport Connections” for detailed
information about SCI interconnects.
You can define default
values for each
section. All Cluster parameter names are case-insensitive, which
differs from parameters specified in my.cnf
or my.ini
files.
With the exception of the MySQL Cluster management server (ndb_mgmd), each node that is part of a MySQL Cluster requires a connectstring that points to the management server's location. This connectstring is used in establishing a connection to the management server as well as in performing other tasks depending on the node's role in the cluster. The syntax for a connectstring is as follows:
<connectstring> := [<nodeid-specification>,]<host-specification>[,<host-specification>] <nodeid-specification> :=node_id
<host-specification> :=host_name
[:port_num
]
node_id
is an integer larger than 1 which
identifies a node in config.ini
.
host_name
is a string representing a
valid Internet host name or IP address.
port_num
is an integer referring to a
TCP/IP port number.
example 1 (long): "nodeid=2,myhost1:1100,myhost2:1100,192.168.0.3:1200" example 2 (short): "myhost1"
All nodes will use localhost:1186
as the
default connectstring value if none is provided. If
port_num
is omitted from the
connectstring, the default port is 1186. This port should always
be available on the network because it has been assigned by IANA
for this purpose (see
http://www.iana.org/assignments/port-numbers for
details).
By listing multiple
<host-specification>
values, it is
possible to designate several redundant management servers. A
cluster node will attempt to contact successive management
servers on each host in the order specified, until a successful
connection has been established.
There are a number of different ways to specify the connectstring:
Each executable has its own command-line option which enables specifying the management server at startup. (See the documentation for the respective executable.)
It is also possible to set the connectstring for all nodes
in the cluster at once by placing it in a
[mysql_cluster]
section in the management
server's my.cnf
file.
For backward compatibility, two other options are available, using the same syntax:
Set the NDB_CONNECTSTRING
environment
variable to contain the connectstring.
Write the connectstring for each executable into a text
file named Ndb.cfg
and place this
file in the executable's startup directory.
However, these are now deprecated and should not be used for new installations.
The recommended method for specifying the connectstring is to
set it on the command line or in the my.cnf
file for each executable.
The maximum length of a connectstring is 1024 characters.
The [computer]
section has no real
significance other than serving as a way to avoid the need of
defining host names for each node in the system. All parameters
mentioned here are required.
The [ndb_mgmd]
section is used to configure
the behavior of the management server. [mgm]
can be used as an alias; the two section names are equivalent.
All parameters in the following list are optional and assume
their default values if omitted.
If neither the ExecuteOnComputer
nor the
HostName
parameter is present, the default
value localhost
will be assumed for both.
Each node in the cluster has a unique identity, which is represented by an integer value in the range 1 to 63 inclusive. This ID is used by all internal cluster messages for addressing the node.
This refers to the Id
set for one of the
computers defined in a [computer]
section
of the config.ini
file.
This is the port number on which the management server listens for configuration requests and management commands.
Specifying this parameter defines the hostname of the
computer on which the management node is to reside. To
specify a hostname other than localhost
,
either this parameter or
ExecuteOnComputer
is required.
This parameter specifies where to send cluster logging
information. There are three options in this regard —
CONSOLE
, SYSLOG
, and
FILE
— with FILE
being the default:
CONSOLE
outputs the log to
stdout
:
CONSOLE
SYSLOG
sends the log to a
syslog
facility, possible values
being one of auth
,
authpriv
, cron
,
daemon
, ftp
,
kern
, lpr
,
mail
, news
,
syslog
, user
,
uucp
, local0
,
local1
, local2
,
local3
, local4
,
local5
, local6
, or
local7
.
Not every facility is necessarily supported by every operating system.
SYSLOG:facility=syslog
FILE
pipes the cluster log output to
a regular file on the same machine. The following values
can be specified:
filename
: The name of the log
file.
maxsize
: The maximum size (in
bytes) to which the file can grow before logging
rolls over to a new file. When this occurs, the old
log file is renamed by appending
.N
to the filename, where
N
is the next number not
yet used with this name.
maxfiles
: The maximum number of
log files.
FILE:filename=cluster.log,maxsize=1000000,maxfiles=6
The default value for the FILE
parameter is
FILE:filename=ndb_
,
where node_id
_cluster.log,maxsize=1000000,maxfiles=6node_id
is the ID of
the node.
It is possible to specify multiple log destinations separated by semicolons as shown here:
CONSOLE;SYSLOG:facility=local0;FILE:filename=/var/log/mgmd
This parameter is used to define which nodes can act as
arbitrators. Only management nodes and SQL nodes can be
arbitrators. ArbitrationRank
can take one
of the following values:
0
: The node will never be used as an
arbitrator.
1
: The node has high priority; that
is, it will be preferred as an arbitrator over
low-priority nodes.
2
: Indicates a low-priority node
which be used as an arbitrator only if a node with a
higher priority is not available for that purpose.
Normally, the management server should be configured as an
arbitrator by setting its ArbitrationRank
to 1 (the default value) and that of all SQL nodes to 0.
An integer value which causes the management server's responses to arbitration requests to be delayed by that number of milliseconds. By default, this value is 0; it is normally not necessary to change it.
This specifies the directory where output files from the
management server will be placed. These files include
cluster log files, process output files, and the daemon's
process ID (PID) file. (For log files, this location can be
overridden by setting the FILE
parameter
for LogDestination
as discussed
previously in this section.)
The default value for this parameter is the directory in which ndb_mgmd is located.
The [ndbd]
and[ndbd
default]
sections are used to configure the behavior of
the cluster's data nodes. There are many parameters which
control buffer sizes, pool sizes, timeouts, and so forth. The
only mandatory parameters are:
Either ExecuteOnComputer
or
HostName
, which must be defined in the
local [ndbd]
section.
The parameter NoOfReplicas
, which must be
defined in the[ndbd default]
section, as
it is common to all Cluster data nodes.
Most data node parameters are set in the [ndbd
default]
section. Only those parameters explicitly
stated as being able to set local values are allowed to be
changed in the [ndbd]
section. Where present,
HostName
, Id
and
ExecuteOnComputer
must
be defined in the local [ndbd]
section, and
not in any other section of config.ini
. In
other words, settings for these parameters are specific to one
data node.
For those parameters affecting memory usage or buffer sizes, it
is possible to use K
, M
,
or G
as a suffix to indicate units of 1024,
1024×1024, or 1024×1024×1024. (For example,
100K
means 100 × 1024 = 102400.)
Parameter names and values are currently case-sensitive.
Identifying data nodes.
The Id
value (that is, the data node
identifier) can be allocated on the command line when the node
is started or in the configuration file.
This is the node ID used as the address of the node for all cluster internal messages. For data nodes, this is an integer in the range 1 to 49 inclusive. Each node in the cluster must have a unique identity.
This refers to the Id
set for one of the
computers defined in a [computer]
section.
Specifying this parameter defines the hostname of the
computer on which the data node is to reside. To specify a
hostname other than localhost
, either
this parameter or ExecuteOnComputer
is
required.
Each node in the cluster uses a port to connect to other nodes. This port is used also for non-TCP transporters in the connection setup phase. The default port is allocated dynamically in such a way as to ensure that no two nodes on the same computer receive the same port number, so it should not normally be necessary to specify a value for this parameter.
This global parameter can be set only in the [ndbd
default]
section, and defines the number of
replicas for each table stored in the cluster. This
parameter also specifies the size of node groups. A node
group is a set of nodes all storing the same information.
Node groups are formed implicitly. The first node group is
formed by the set of data nodes with the lowest node IDs,
the next node group by the set of the next lowest node
identities, and so on. By way of example, assume that we
have 4 data nodes and that NoOfReplicas
is set to 2. The four data nodes have node IDs 2, 3, 4 and
5. Then the first node group is formed from nodes 2 and 3,
and the second node group by nodes 4 and 5. It is important
to configure the cluster in such a manner that nodes in the
same node groups are not placed on the same computer because
a single hardware failure would cause the entire cluster to
crash.
If no node IDs are provided, the order of the data nodes
will be the determining factor for the node group. Whether
or not explicit assignments are made, they can be viewed in
the output of the management client's
SHOW
statement.
There is no default value for
NoOfReplicas
; the maximum possible value
is 4. For production clusters, it is recommended that this
parameter be set to 1 or 2.
The value for this parameter must divide evenly into the
number of data nodes in the cluster. For example, if there
are two data nodes, then NoOfReplicas
must be equal to either 1 or 2, since 2/3 and 2/4 both
yield fractional values; if there are four data nodes,
then NoOfReplicas
must be equal to 1,
2, or 4.
This parameter specifies the directory where trace files, log files, pid files and error logs are placed.
This parameter specifies the directory where all files
created for metadata, REDO logs, UNDO logs and data files
are placed. The default is the directory specified by
DataDir
.
This directory must exist before the ndbd process is initiated.
The recommended directory hierarchy for MySQL Cluster
includes /var/lib/mysql-cluster
, under
which a directory for the node's filesystem is created. The
name of this subdirectory contains the node ID. For example,
if the node ID is 2, this subdirectory is named
ndb_2_fs
.
This parameter specifies the directory in which backups are
placed. If omitted, the default backup location is the
directory named BACKUP
under the
location specified by the FileSystemPath
parameter. (See above.)
Data Memory, Index Memory, and String Memory
DataMemory
and IndexMemory
are [ndbd]
parameters specifying the size of
memory segments used to store the actual records and their
indexes. In setting values for these, it is important to
understand how DataMemory
and
IndexMemory
are used, as they usually need to
be updated to reflect actual usage by the cluster:
This parameter defines the amount of space (in bytes) available for storing database records. The entire amount specified by this value is allocated in memory, so it is extremely important that the machine has sufficient physical memory to accommodate it.
The memory allocated by DataMemory
is
used to store both the actual records and indexes. Each
record is currently of fixed size. (Even
VARCHAR
columns are stored as fixed-width
columns.) There is a 16-byte overhead on each record; an
additional amount for each record is incurred because it is
stored in a 32KB page with 128 byte page overhead (see
below). There is also a small amount wasted per page due to
the fact that each record is stored in only one page.
The maximum record size is currently 8052 bytes.
The memory space defined by DataMemory
is
also used to store ordered indexes, which use about 10 bytes
per record. Each table row is represented in the ordered
index. A common error among users is to assume that all
indexes are stored in the memory allocated by
IndexMemory
, but this is not the case:
Only primary key and unique hash indexes use this memory;
ordered indexes use the memory allocated by
DataMemory
. However, creating a primary
key or unique hash index also creates an ordered index on
the same keys, unless you specify USING
HASH
in the index creation statement. This can be
verified by running ndb_desc -d
db_name
table_name
in the
management client.
The memory space allocated by DataMemory
consists of 32KB pages, which are allocated to table
fragments. Each table is normally partitioned into the same
number of fragments as there are data nodes in the cluster.
Thus, for each node, there are the same number of fragments
as are set in NoOfReplicas
.
Once a page has been allocated, it is currently not possible
to return it to the pool of free pages, except by deleting
the table. (This also means that
DataMemory
pages, once allocated to a
given table, cannot be used by other tables.) Performing a
node recovery also compresses the partition because all
records are inserted into empty partitions from other live
nodes.
The DataMemory
memory space also contains
UNDO information: For each update, a copy of the unaltered
record is allocated in the DataMemory
.
There is also a reference to each copy in the ordered table
indexes. Unique hash indexes are updated only when the
unique index columns are updated, in which case a new entry
in the index table is inserted and the old entry is deleted
upon commit. For this reason, it is also necessary to
allocate enough memory to handle the largest transactions
performed by applications using the cluster. In any case,
performing a few large transactions holds no advantage over
using many smaller ones, for the following reasons:
Large transactions are not any faster than smaller ones
Large transactions increase the number of operations that are lost and must be repeated in event of transaction failure
Large transactions use more memory
The default value for DataMemory
is 80MB;
the minimum is 1MB. There is no maximum size, but in reality
the maximum size has to be adapted so that the process does
not start swapping when the limit is reached. This limit is
determined by the amount of physical RAM available on the
machine and by the amount of memory that the operating
system may commit to any one process. 32-bit operating
systems are generally limited to 2–4GB per process;
64-bit operating systems can use more. For large databases,
it may be preferable to use a 64-bit operating system for
this reason.
This parameter controls the amount of storage used for hash indexes in MySQL Cluster. Hash indexes are always used for primary key indexes, unique indexes, and unique constraints. Note that when defining a primary key and a unique index, two indexes will be created, one of which is a hash index used for all tuple accesses as well as lock handling. It is also used to enforce unique constraints.
The size of the hash index is 25 bytes per record, plus the size of the primary key. For primary keys larger than 32 bytes another 8 bytes is added.
The default value for IndexMemory
is
18MB. The minimum is 1MB.
This parameter determines how much memory is allocated for
strings such as table names, and is specified in an
[ndbd]
or [ndbd
default]
section of the
config.ini
file. A value between
0
and 100
inclusive is
interpreted as a percent of the maximum default value, which
is calculated based on a number of factors including the
number of tables, maximum table name size, maximum size of
.FRM
files,
MaxNoOfTriggers
, maximum column name
size, and maximum default column value. In general it is
safe to assume that the maximum default value is
approximately 5 MB for a MySQL Cluster having 1000 tables.
A value greater than 100
is interpreted
as a number of bytes.
In MySQL 5.0, the default value is
100
— that is, 100 percent of the
default maximum, or roughly 5 MB. It is possible to reduce
this value safely, but it should never be less than 5
percent. If you encounter Error 773 Out of string
memory, please modify StringMemory config parameter:
Permanent error: Schema error, this means that
means that you have set the StringMemory
value too low. 25
(25 percent) is not
excessive, and should prevent this error from recurring in
all but the most extreme conditions, as when there are
hundreds or thousands of NDB
tables with
names whose lengths and columns whose number approach their
permitted maximums.
The following example illustrates how memory is used for a table. Consider this table definition:
CREATE TABLE example ( a INT NOT NULL, b INT NOT NULL, c INT NOT NULL, PRIMARY KEY(a), UNIQUE(b) ) ENGINE=NDBCLUSTER;
For each record, there are 12 bytes of data plus 12 bytes
overhead. Having no nullable columns saves 4 bytes of overhead.
In addition, we have two ordered indexes on columns
a
and b
consuming roughly
10 bytes each per record. There is a primary key hash index on
the base table using roughly 29 bytes per record. The unique
constraint is implemented by a separate table with
b
as primary key and a
as
a column. This other table consumes an additional 29 bytes of
index memory per record in the example
table
as well 8 bytes of record data plus 12 bytes of overhead.
Thus, for one million records, we need 58MB for index memory to handle the hash indexes for the primary key and the unique constraint. We also need 64MB for the records of the base table and the unique index table, plus the two ordered index tables.
You can see that hash indexes takes up a fair amount of memory space; however, they provide very fast access to the data in return. They are also used in MySQL Cluster to handle uniqueness constraints.
Currently, the only partitioning algorithm is hashing and ordered indexes are local to each node. Thus, ordered indexes cannot be used to handle uniqueness constraints in the general case.
An important point for both IndexMemory
and
DataMemory
is that the total database size is
the sum of all data memory and all index memory for each node
group. Each node group is used to store replicated information,
so if there are four nodes with two replicas, there will be two
node groups. Thus, the total data memory available is 2 ×
DataMemory
for each data node.
It is highly recommended that DataMemory
and
IndexMemory
be set to the same values for all
nodes. Data distribution is even over all nodes in the cluster,
so the maximum amount of space available for any node can be no
greater than that of the smallest node in the cluster.
DataMemory
and IndexMemory
can be changed, but decreasing either of these can be risky;
doing so can easily lead to a node or even an entire MySQL
Cluster that is unable to restart due to there being
insufficient memory space. Increasing these values should be
acceptable, but it is recommended that such upgrades are
performed in the same manner as a software upgrade, beginning
with an update of the configuration file, and then restarting
the management server followed by restarting each data node in
turn.
Updates do not increase the amount of index memory used. Inserts take effect immediately; however, rows are not actually deleted until the transaction is committed.
Transaction parameters.
The next three [ndbd]
parameters that we
discuss are important because they affect the number of
parallel transactions and the sizes of transactions that can
be handled by the system.
MaxNoOfConcurrentTransactions
sets the
number of parallel transactions possible in a node.
MaxNoOfConcurrentOperations
sets the number
of records that can be in update phase or locked
simultaneously.
Both of these parameters (especially
MaxNoOfConcurrentOperations
) are likely
targets for users setting specific values and not using the
default value. The default value is set for systems using small
transactions, to ensure that these do not use excessive memory.
Each cluster data node requires a transaction record for each active transaction in the cluster. The task of coordinating transactions is distributed among all of the data nodes. The total number of transaction records in the cluster is the number of transactions in any given node times the number of nodes in the cluster.
Transaction records are allocated to individual MySQL servers. Each connection to a MySQL server requires at least one transaction record, plus an additional transaction object per table accessed by that connection. This means that a reasonable minimum for this parameter is
MaxNoOfConcurrentTransactions = (maximum number of tables accessed in any single transaction + 1) * number of cluster SQL nodes
For example, suppose that there are 4 SQL nodes using the cluster. A single join involving 5 tables requires 6 transaction records; if there are 5 such joins in a transaction, then 5 * 6 = 30 transaction records are required for this transaction, per MySQL server, or 30 * 4 = 120 transaction records total.
This parameter must be set to the same value for all cluster data nodes. This is due to the fact that, when a data node fails, the oldest surviving node re-creates the transaction state of all transactions that were ongoing in the failed node.
Changing the value of
MaxNoOfConcurrentTransactions
requires a
complete shutdown and restart of the cluster.
The default value is 4096.
It is a good idea to adjust the value of this parameter according to the size and number of transactions. When performing transactions of only a few operations each and not involving a great many records, there is no need to set this parameter very high. When performing large transactions involving many records need to set this parameter higher.
Records are kept for each transaction updating cluster data, both in the transaction coordinator and in the nodes where the actual updates are performed. These records contain state information needed to find UNDO records for rollback, lock queues, and other purposes.
This parameter should be set to the number of records to be updated simultaneously in transactions, divided by the number of cluster data nodes. For example, in a cluster which has four data nodes and which is expected to handle 1,000,000 concurrent updates using transactions, you should set this value to 1000000 / 4 = 250000.
Read queries which set locks also cause operation records to be created. Some extra space is allocated within individual nodes to accommodate cases where the distribution is not perfect over the nodes.
When queries make use of the unique hash index, there are actually two operation records used per record in the transaction. The first record represents the read in the index table and the second handles the operation on the base table.
The default value is 32768.
This parameter actually handles two values that can be configured separately. The first of these specifies how many operation records are to be placed with the transaction coordinator. The second part specifies how many operation records are to be local to the database.
A very large transaction performed on an eight-node cluster
requires as many operation records in the transaction
coordinator as there are reads, updates, and deletes
involved in the transaction. However, the operation records
of the are spread over all eight nodes. Thus, if it is
necessary to configure the system for one very large
transaction, it is a good idea to configure the two parts
separately. MaxNoOfConcurrentOperations
will always be used to calculate the number of operation
records in the transaction coordinator portion of the node.
It is also important to have an idea of the memory requirements for operation records. These consume about 1KB per record.
By default, this parameter is calculated as 1.1 ×
MaxNoOfConcurrentOperations
. This fits
systems with many simultaneous transactions, none of them
being very large. If there is a need to handle one very
large transaction at a time and there are many nodes, it is
a good idea to override the default value by explicitly
specifying this parameter.
Transaction temporary storage.
The next set of [ndbd]
parameters is used
to determine temporary storage when executing a statement that
is part of a Cluster transaction. All records are released
when the statement is completed and the cluster is waiting for
the commit or rollback.
The default values for these parameters are adequate for most situations. However, users with a need to support transactions involving large numbers of rows or operations may need to increase these values to enable better parallelism in the system, whereas users whose applications require relatively small transactions can decrease the values to save memory.
MaxNoOfConcurrentIndexOperations
For queries using a unique hash index, another temporary set
of operation records is used during a query's execution
phase. This parameter sets the size of that pool of records.
Thus, this record is allocated only while executing a part
of a query. As soon as this part has been executed, the
record is released. The state needed to handle aborts and
commits is handled by the normal operation records, where
the pool size is set by the parameter
MaxNoOfConcurrentOperations
.
The default value of this parameter is 8192. Only in rare cases of extremely high parallelism using unique hash indexes should it be necessary to increase this value. Using a smaller value is possible and can save memory if the DBA is certain that a high degree of parallelism is not required for the cluster.
The default value of MaxNoOfFiredTriggers
is 4000, which is sufficient for most situations. In some
cases it can even be decreased if the DBA feels certain the
need for parallelism in the cluster is not high.
A record is created when an operation is performed that affects a unique hash index. Inserting or deleting a record in a table with unique hash indexes or updating a column that is part of a unique hash index fires an insert or a delete in the index table. The resulting record is used to represent this index table operation while waiting for the original operation that fired it to complete. This operation is short-lived but can still require a large number of records in its pool for situations with many parallel write operations on a base table containing a set of unique hash indexes.
The memory affected by this parameter is used for tracking operations fired when updating index tables and reading unique indexes. This memory is used to store the key and column information for these operations. It is only very rarely that the value for this parameter needs to be altered from the default.
The default value for
TransactionBufferMemory
is 1MB.
Normal read and write operations use a similar buffer, whose
usage is even more short-lived. The compile-time parameter
ZATTRBUF_FILESIZE
(found in
ndb/src/kernel/blocks/Dbtc/Dbtc.hpp
)
set to 4000 × 128 bytes (500KB). A similar buffer for
key information, ZDATABUF_FILESIZE
(also
in Dbtc.hpp
) contains 4000 × 16 =
62.5KB of buffer space. Dbtc
is the
module that handles transaction coordination.
Scans and buffering.
There are additional [ndbd]
parameters in
the Dblqh
module (in
ndb/src/kernel/blocks/Dblqh/Dblqh.hpp
)
that affect reads and updates. These include
ZATTRINBUF_FILESIZE
, set by default to
10000 × 128 bytes (1250KB) and
ZDATABUF_FILE_SIZE
, set by default to
10000*16 bytes (roughly 156KB) of buffer space. To date, there
have been neither any reports from users nor any results from
our own extensive tests suggesting that either of these
compile-time limits should be increased.
This parameter is used to control the number of parallel
scans that can be performed in the cluster. Each transaction
coordinator can handle the number of parallel scans defined
for this parameter. Each scan query is performed by scanning
all partitions in parallel. Each partition scan uses a scan
record in the node where the partition is located, the
number of records being the value of this parameter times
the number of nodes. The cluster should be able to sustain
MaxNoOfConcurrentScans
scans concurrently
from all nodes in the cluster.
Scans are actually performed in two cases. The first of these cases occurs when no hash or ordered indexes exists to handle the query, in which case the query is executed by performing a full table scan. The second case is encountered when there is no hash index to support the query but there is an ordered index. Using the ordered index means executing a parallel range scan. The order is kept on the local partitions only, so it is necessary to perform the index scan on all partitions.
The default value of
MaxNoOfConcurrentScans
is 256. The
maximum value is 500.
Specifies the number of local scan records if many scans are
not fully parallelized. If the number of local scan records
is not provided, it is calculated as the product of
MaxNoOfConcurrentScans
and the number of
data nodes in the system. The minimum value is 32.
This parameter is used to calculate the number of lock records which must be there to handle many concurrent scan operations.
The default value is 64; this value has a strong connection
to the ScanBatchSize
defined in the SQL
nodes.
This is an internal buffer used for passing messages within individual nodes and between nodes. Although it is highly unlikely that this would need to be changed, it is configurable. By default, it is set to 1MB.
Logging and checkpointing.
These [ndbd]
parameters control log and
checkpoint behavior.
This parameter sets the number of REDO log files for the node, and thus the amount of space allocated to REDO logging. Because the REDO log files are organized in a ring, it is extremely important that the first and last log files in the set (sometimes referred to as the “head” and “tail” log files, respectively) do not meet. When these approach one another too closely, the node begins aborting all transactions encompassing updates due to a lack of room for new log records.
A REDO
log record is not removed until
three local checkpoints have been completed since that log
record was inserted. Checkpointing frequency is determined
by its own set of configuration parameters discussed
elsewhere in this chapter.
How these parameters interact and proposals for how to configure them are discussed in Section 16.3.6, “Configuring Parameters for Local Checkpoints”.
The default parameter value is 8, which means 8 sets of 4
16MB files for a total of 512MB. In other words, REDO log
space must be allocated in blocks of 64MB. In scenarios
requiring a great many updates, the value for
NoOfFragmentLogFiles
may need to be set
as high as 300 or even higher to provide sufficient space
for REDO logs.
If the checkpointing is slow and there are so many writes to
the database that the log files are full and the log tail
cannot be cut without jeopardizing recovery, all updating
transactions are aborted with internal error code 410
(Out of log file space temporarily
). This
condition prevails until a checkpoint has completed and the
log tail can be moved forward.
This parameter cannot be changed “on the
fly”; you must restart the node using
--initial
. If you wish to change this
value for a running cluster, you can do so via a rolling
node restart.
This parameter sets a ceiling on how many internal threads to allocate for open files. Any situation requiring a change in this parameter should be reported as a bug.
The default value is 40.
This parameter sets the maximum number of trace files that are kept before overwriting old ones. Trace files are generated when, for whatever reason, the node crashes.
The default is 25 trace files.
Metadata objects.
The next set of [ndbd]
parameters defines
pool sizes for metadata objects, used to define the maximum
number of attributes, tables, indexes, and trigger objects
used by indexes, events, and replication between clusters.
Note that these act merely as “suggestions” to
the cluster, and any that are not specified revert to the
default values shown.
Defines the number of attributes that can be defined in the cluster.
The default value is 1000, with the minimum possible value being 32. The maximum is 4294967039. Each attribute consumes around 200 bytes of storage per node due to the fact that all metadata is fully replicated on the servers.
When setting MaxNoOfAttributes
, it is
important to prepare in advance for any ALTER
TABLE
statements that you might want to perform in
the future. This is due to the fact, during the execution of
ALTER TABLE
on a Cluster table, 3 times
the number of attributes as in the original table are used.
For example, if a table requires 100 attributes, and you
want to be able to alter it later, you need to set the value
of MaxNoOfAttributes
to 300. Assuming
that you can create all desired tables without any problems,
a good rule of thumb is to add two times the number of
attributes in the largest table to
MaxNoOfAttributes
to be sure. You should
also verify that this number is sufficient by trying an
actual ALTER TABLE
after configuring the
parameter. If this is not successful, increase
MaxNoOfAttributes
by another multiple of
the original value and test it again.
A table object is allocated for each table, unique hash index, and ordered index. This parameter sets the maximum number of table objects for the cluster as a whole.
For each attribute that has a BLOB
data
type an extra table is used to store most of the
BLOB
data. These tables also must be
taken into account when defining the total number of tables.
The default value of this parameter is 128. The minimum is 8 and the maximum is 1600. Each table object consumes approximately 20KB per node.
For each ordered index in the cluster, an object is allocated describing what is being indexed and its storage segments. By default, each index so defined also defines an ordered index. Each unique index and primary key has both an ordered index and a hash index.
The default value of this parameter is 128. Each object consumes approximately 10KB of data per node.
For each unique index that is not a primary key, a special
table is allocated that maps the unique key to the primary
key of the indexed table. By default, an ordered index is
also defined for each unique index. To prevent this, you
must specify the USING HASH
option when
defining the unique index.
The default value is 64. Each index consumes approximately 15KB per node.
Internal update, insert, and delete triggers are allocated for each unique hash index. (This means that three triggers are created for each unique hash index.) However, an ordered index requires only a single trigger object. Backups also use three trigger objects for each normal table in the cluster.
This parameter sets the maximum number of trigger objects in the cluster.
The default value is 768.
This parameter is deprecated in MySQL 5.0; you
should use MaxNoOfOrderedIndexes
and
MaxNoOfUniqueHashIndexes
instead.
This parameter is used only by unique hash indexes. There needs to be one record in this pool for each unique hash index defined in the cluster.
The default value of this parameter is 128.
Boolean parameters.
The behavior of data nodes is also affected by a set of
[ndbd]
parameters taking on boolean values.
These parameters can each be specified as
TRUE
by setting them equal to
1
or Y
, and as
FALSE
by setting them equal to
0
or N
.
For a number of operating systems, including Solaris and Linux, it is possible to lock a process into memory and so avoid any swapping to disk. This can be used to help guarantee the cluster's real-time characteristics.
Beginning with MySQL 5.0.36, this parameter takes one of the
integer values 0
, 1
,
or 2
, which act as follows:
0
: Disables locking. This is the
default value.
1
: Performs the lock after allocating
memory for the process.
2
: Performs the lock before memory
for the process is allocated.
Previously, this parameter was a Boolean.
0
or false
was the
default setting, and disabled locking. 1
or true
enabled locking of the process
after its memory was allocated.
Beginning with MySQL 5.0.36, it is no longer possible to
use true
or false
for the value of this parameter; when upgrading from a
previous version, you must change the value to
0
, 1
, or
2
.
This parameter specifies whether an ndbd process should exit or perform an automatic restart when an error condition is encountered.
This feature is enabled by default.
It is possible to specify MySQL Cluster tables as diskless, meaning that tables are not checkpointed to disk and that no logging occurs. Such tables exist only in main memory. A consequence of using diskless tables is that neither the tables nor the records in those tables survive a crash. However, when operating in diskless mode, it is possible to run ndbd on a diskless computer.
This feature causes the entire cluster to operate in diskless mode.
When this feature is enabled, Cluster online backup is disabled. In addition, a partial start of the cluster is not possible.
Diskless
is disabled by default.
This feature is accessible only when building the debug version where it is possible to insert errors in the execution of individual blocks of code as part of testing.
This feature is disabled by default.
Controlling Timeouts, Intervals, and Disk Paging
There are a number of [ndbd]
parameters
specifying timeouts and intervals between various actions in
Cluster data nodes. Most of the timeout values are specified in
milliseconds. Any exceptions to this are mentioned where
applicable.
To prevent the main thread from getting stuck in an endless loop at some point, a “watchdog” thread checks the main thread. This parameter specifies the number of milliseconds between checks. If the process remains in the same state after three checks, the watchdog thread terminates it.
This parameter can easily be changed for purposes of experimentation or to adapt to local conditions. It can be specified on a per-node basis although there seems to be little reason for doing so.
The default timeout is 4000 milliseconds (4 seconds).
This parameter specifies how long the Cluster waits for all data nodes to come up before the cluster initialization routine is invoked. This timeout is used to avoid a partial Cluster startup whenever possible.
The default value is 30000 milliseconds (30 seconds). 0 disables the timeout, in which case the cluster may start only if all nodes are available.
If the cluster is ready to start after waiting for
StartPartialTimeout
milliseconds but is
still possibly in a partitioned state, the cluster waits
until this timeout has also passed.
The default timeout is 60000 milliseconds (60 seconds).
If a data node has not completed its startup sequence within the time specified by this parameter, the node startup fails. Setting this parameter to 0 (the default value) means that no data node timeout is applied.
For nonzero values, this parameter is measured in milliseconds. For data nodes containing extremely large amounts of data, this parameter should be increased. For example, in the case of a data node containing several gigabytes of data, a period as long as 10–15 minutes (that is, 600000 to 1000000 milliseconds) might be required to perform a node restart.
One of the primary methods of discovering failed nodes is by the use of heartbeats. This parameter states how often heartbeat signals are sent and how often to expect to receive them. After missing three heartbeat intervals in a row, the node is declared dead. Thus, the maximum time for discovering a failure through the heartbeat mechanism is four times the heartbeat interval.
The default heartbeat interval is 1500 milliseconds (1.5 seconds). This parameter must not be changed drastically and should not vary widely between nodes. If one node uses 5000 milliseconds and the node watching it uses 1000 milliseconds, obviously the node will be declared dead very quickly. This parameter can be changed during an online software upgrade, but only in small increments.
Each data node sends heartbeat signals to each MySQL server
(SQL node) to ensure that it remains in contact. If a MySQL
server fails to send a heartbeat in time it is declared
“dead,” in which case all ongoing transactions
are completed and all resources released. The SQL node
cannot reconnect until all activities initiated by the
previous MySQL instance have been completed. The
three-heartbeat criteria for this determination are the same
as described for HeartbeatIntervalDbDb
.
The default interval is 1500 milliseconds (1.5 seconds). This interval can vary between individual data nodes because each data node watches the MySQL servers connected to it, independently of all other data nodes.
This parameter is an exception in that it does not specify a time to wait before starting a new local checkpoint; rather, it is used to ensure that local checkpoints are not performed in a cluster where relatively few updates are taking place. In most clusters with high update rates, it is likely that a new local checkpoint is started immediately after the previous one has been completed.
The size of all write operations executed since the start of the previous local checkpoints is added. This parameter is also exceptional in that it is specified as the base-2 logarithm of the number of 4-byte words, so that the default value 20 means 4MB (4 × 220) of write operations, 21 would mean 8MB, and so on up to a maximum value of 31, which equates to 8GB of write operations.
All the write operations in the cluster are added together.
Setting TimeBetweenLocalCheckpoints
to 6
or less means that local checkpoints will be executed
continuously without pause, independent of the cluster's
workload.
When a transaction is committed, it is committed in main memory in all nodes on which the data is mirrored. However, transaction log records are not flushed to disk as part of the commit. The reasoning behind this behavior is that having the transaction safely committed on at least two autonomous host machines should meet reasonable standards for durability.
It is also important to ensure that even the worst of cases — a complete crash of the cluster — is handled properly. To guarantee that this happens, all transactions taking place within a given interval are put into a global checkpoint, which can be thought of as a set of committed transactions that has been flushed to disk. In other words, as part of the commit process, a transaction is placed in a global checkpoint group. Later, this group's log records are flushed to disk, and then the entire group of transactions is safely committed to disk on all computers in the cluster.
This parameter defines the interval between global checkpoints. The default is 2000 milliseconds.
TimeBetweenInactiveTransactionAbortCheck
Timeout handling is performed by checking a timer on each transaction once for every interval specified by this parameter. Thus, if this parameter is set to 1000 milliseconds, every transaction will be checked for timing out once per second.
The default value is 1000 milliseconds (1 second).
This parameter states the maximum time that is permitted to lapse between operations in the same transaction before the transaction is aborted.
The default for this parameter is zero (no timeout). For a real-time database that needs to ensure that no transaction keeps locks for too long, this parameter should be set to a relatively small value. The unit is milliseconds.
TransactionDeadlockDetectionTimeout
When a node executes a query involving a transaction, the node waits for the other nodes in the cluster to respond before continuing. A failure to respond can occur for any of the following reasons:
The node is “dead”
The operation has entered a lock queue
The node requested to perform the action could be heavily overloaded.
This timeout parameter states how long the transaction coordinator waits for query execution by another node before aborting the transaction, and is important for both node failure handling and deadlock detection. In MySQL 5.0.20 and earlier versions, setting it too high could cause undesirable behavior in situations involving deadlocks and node failure. Beginning with MySQL 5.0.21, active transactions occurring during node failures are actively aborted by the Cluster Transaction Coordinator, and so high settings are no longer an issue with this parameter.
The default timeout value is 1200 milliseconds (1.2 seconds).
NoOfDiskPagesToDiskAfterRestartTUP
When executing a local checkpoint, the algorithm flushes all
data pages to disk. Merely doing so as quickly as possible
without any moderation is likely to impose excessive loads
on processors, networks, and disks. To control the write
speed, this parameter specifies how many pages per 100
milliseconds are to be written. In this context, a
“page” is defined as 8KB. This parameter is
specified in units of 80KB per second, so setting
NoOfDiskPagesToDiskAfterRestartTUP
to a
value of 20
entails writing 1.6MB in data
pages to disk each second during a local checkpoint. This
value includes the writing of UNDO log records for data
pages. That is, this parameter handles the limitation of
writes from data memory. UNDO log records for index pages
are handled by the parameter
NoOfDiskPagesToDiskAfterRestartACC
. (See
the entry for IndexMemory
for information
about index pages.)
In short, this parameter specifies how quickly to execute
local checkpoints. It operates in conjunction with
NoOfFragmentLogFiles
,
DataMemory
, and
IndexMemory
.
For more information about the interaction between these parameters and possible strategies for choosing appropriate values for them, see Section 16.3.6, “Configuring Parameters for Local Checkpoints”.
The default value is 40 (3.2MB of data pages per second).
NoOfDiskPagesToDiskAfterRestartACC
This parameter uses the same units as
NoOfDiskPagesToDiskAfterRestartTUP
and
acts in a similar fashion, but limits the speed of writing
index pages from index memory.
The default value of this parameter is 20 (1.6MB of index memory pages per second).
NoOfDiskPagesToDiskDuringRestartTUP
This parameter is used in a fashion similar to
NoOfDiskPagesToDiskAfterRestartTUP
and
NoOfDiskPagesToDiskAfterRestartACC
, only
it does so with regard to local checkpoints executed in the
node when a node is restarting. A local checkpoint is always
performed as part of all node restarts. During a node
restart it is possible to write to disk at a higher speed
than at other times, because fewer activities are being
performed in the node.
This parameter covers pages written from data memory.
The default value is 40 (3.2MB per second).
NoOfDiskPagesToDiskDuringRestartACC
Controls the number of index memory pages that can be written to disk during the local checkpoint phase of a node restart.
As with
NoOfDiskPagesToDiskAfterRestartTUP
and
NoOfDiskPagesToDiskAfterRestartACC
,
values for this parameter are expressed in terms of 8KB
pages written per 100 milliseconds (80KB/second).
The default value is 20 (1.6MB per second).
This parameter specifies how long data nodes wait for a response from the arbitrator to an arbitration message. If this is exceeded, the network is assumed to have split.
The default value is 1000 milliseconds (1 second).
Buffering and logging.
Several [ndbd]
configuration parameters
corresponding to former compile-time parameters were
introduced in MySQL 4.1.5. These enable the advanced user to
have more control over the resources used by node processes
and to adjust various buffer sizes at need.
These buffers are used as front ends to the file system when
writing log records to disk. If the node is running in diskless
mode, these parameters can be set to their minimum values
without penalty due to the fact that disk writes are
“faked” by the NDB
storage
engine's filesystem abstraction layer.
The UNDO index buffer, whose size is set by this parameter,
is used during local checkpoints. The NDB
storage engine uses a recovery scheme based on checkpoint
consistency in conjunction with an operational REDO log. To
produce a consistent checkpoint without blocking the entire
system for writes, UNDO logging is done while performing the
local checkpoint. UNDO logging is activated on a single
table fragment at a time. This optimization is possible
because tables are stored entirely in main memory.
The UNDO index buffer is used for the updates on the primary key hash index. Inserts and deletes rearrange the hash index; the NDB storage engine writes UNDO log records that map all physical changes to an index page so that they can be undone at system restart. It also logs all active insert operations for each fragment at the start of a local checkpoint.
Reads and updates set lock bits and update a header in the hash index entry. These changes are handled by the page-writing algorithm to ensure that these operations need no UNDO logging.
This buffer is 2MB by default. The minimum value is 1MB,
which is sufficient for most applications. For applications
doing extremely large or numerous inserts and deletes
together with large transactions and large primary keys, it
may be necessary to increase the size of this buffer. If
this buffer is too small, the NDB storage engine issues
internal error code 677 (Index UNDO buffers
overloaded
).
It is not safe to decrease the value of this parameter during a rolling restart.
This parameter sets the size of the UNDO data buffer, which performs a function similar to that of the UNDO index buffer, except the UNDO data buffer is used with regard to data memory rather than index memory. This buffer is used during the local checkpoint phase of a fragment for inserts, deletes, and updates.
Because UNDO log entries tend to grow larger as more operations are logged, this buffer is also larger than its index memory counterpart, with a default value of 16MB.
This amount of memory may be unnecessarily large for some applications. In such cases, it is possible to decrease this size to a minimum of 1MB.
It is rarely necessary to increase the size of this buffer. If there is such a need, it is a good idea to check whether the disks can actually handle the load caused by database update activity. A lack of sufficient disk space cannot be overcome by increasing the size of this buffer.
If this buffer is too small and gets congested, the NDB storage engine issues internal error code 891 (Data UNDO buffers overloaded).
It is not safe to decrease the value of this parameter during a rolling restart.
All update activities also need to be logged. The REDO log makes it possible to replay these updates whenever the system is restarted. The NDB recovery algorithm uses a “fuzzy” checkpoint of the data together with the UNDO log, and then applies the REDO log to play back all changes up to the restoration point.
RedoBuffer
sets the size of the buffer
inwhich the REDO log is written, and is 8MB by default. The
minimum value is 1MB.
If this buffer is too small, the NDB storage engine issues
error code 1221 (REDO log buffers
overloaded
).
It is not safe to decrease the value of this parameter during a rolling restart.
Controlling log messages.
In managing the cluster, it is very important to be able to
control the number of log messages sent for various event
types to stdout
. For each event category,
there are 16 possible event levels (numbered 0 through 15).
Setting event reporting for a given event category to level 15
means all event reports in that category are sent to
stdout
; setting it to 0 means that there
will be no event reports made in that category.
By default, only the startup message is sent to
stdout
, with the remaining event reporting
level defaults being set to 0. The reason for this is that these
messages are also sent to the management server's cluster log.
An analogous set of levels can be set for the management client to determine which event levels to record in the cluster log.
The reporting level for events generated during startup of the process.
The default level is 1.
The reporting level for events generated as part of graceful shutdown of a node.
The default level is 0.
The reporting level for statistical events such as number of primary key reads, number of updates, number of inserts, information relating to buffer usage, and so on.
The default level is 0.
The reporting level for events generated by local and global checkpoints.
The default level is 0.
The reporting level for events generated during node restart.
The default level is 0.
The reporting level for events generated by connections between cluster nodes.
The default level is 0.
The reporting level for events generated by errors and warnings by the cluster as a whole. These errors do not cause any node failure but are still considered worth reporting.
The default level is 0.
The reporting level for events generated by congestion. These errors do not cause node failure but are still considered worth reporting.
The default level is 0.
The reporting level for events generated for information about the general state of the cluster.
The default level is 0.
Backup parameters.
The [ndbd]
parameters discussed in this
section define memory buffers set aside for execution of
online backups.
In creating a backup, there are two buffers used for sending
data to the disk. The backup data buffer is used to fill in
data recorded by scanning a node's tables. Once this buffer
has been filled to the level specified as
BackupWriteSize
(see below), the pages
are sent to disk. While flushing data to disk, the backup
process can continue filling this buffer until it runs out
of space. When this happens, the backup process pauses the
scan and waits until some disk writes have completed freed
up memory so that scanning may continue.
The default value is 2MB.
The backup log buffer fulfills a role similar to that played by the backup data buffer, except that it is used for generating a log of all table writes made during execution of the backup. The same principles apply for writing these pages as with the backup data buffer, except that when there is no more space in the backup log buffer, the backup fails. For that reason, the size of the backup log buffer must be large enough to handle the load caused by write activities while the backup is being made. See Section 16.9.4, “Configuration for Cluster Backup”.
The default value for this parameter should be sufficient for most applications. In fact, it is more likely for a backup failure to be caused by insufficient disk write speed than it is for the backup log buffer to become full. If the disk subsystem is not configured for the write load caused by applications, the cluster is unlikely to be able to perform the desired operations.
It is preferable to configure cluster nodes in such a manner that the processor becomes the bottleneck rather than the disks or the network connections.
The default value is 2MB.
This parameter is simply the sum of
BackupDataBufferSize
and
BackupLogBufferSize
.
The default value is 2MB + 2MB = 4MB.
If BackupDataBufferSize
and
BackupLogBufferSize
taken together
exceed 4MB, then this parameter must be set explicitly in
the config.ini
file to their sum.
This parameter specifies the default size of messages written to disk by the backup log and backup data buffers.
The default value is 32KB.
This parameter specifies the maximum size of messages written to disk by the backup log and backup data buffers.
The default value is 256KB.
When specifying these parameters, the following relationships must hold true. Otherwise, the data node will be unable to start.
BackupDataBufferSize >= BackupWriteSize +
188KB
BackupLogBufferSize >= BackupWriteSize +
16KB
BackupMaxWriteSize >= BackupWriteSize
The [mysqld]
and [api]
sections in the config.ini
file define the
behavior of the MySQL servers (SQL nodes) and other applications
(API nodes) used to access cluster data. None of the parameters
shown is required. If no computer or host name is provided, any
host can use this SQL or API node.
Generally speaking, a [mysqld]
section is
used to indicate a MySQL server providing an SQL interface to
the cluster, and an [api]
section is used for
applications other than mysqld processes
accessing cluster data, but the two designations are actually
synonomous; you can, for instance, list parameters for a MySQL
server acting as an SQL node in an [api]
section.
For a discussion of MySQL server options for MySQL Cluster, see Section 16.4.2, “MySQL Cluster-Related Command Options for mysqld”; for information about MySQL server system variables relating to MySQL Cluster, see Section 16.4.3, “MySQL Cluster System Variables”.
The Id
value is used to identify the node
in all cluster internal messages. It must be an integer in
the range 1 to 63 inclusive, and must be unique among all
node IDs within the cluster.
This refers to the Id
set for one of the
computers (hosts) defined in a [computer]
section of the configuration file.
Specifying this parameter defines the hostname of the
computer on which the SQL node (API node) is to reside. To
specify a hostname, either this parameter or
ExecuteOnComputer
is required.
If no HostName
or
ExecuteOnComputer
is specified in a given
[mysql]
or [api]
section of the config.ini
file, then an
SQL or API node may connect using the corresponding
“slot” from any host which can establish a
network connection to the management server host machine.
This differs from the default behavior for data
nodes, where localhost
is assumed for
HostName
unless otherwise
specified.
This parameter defines which nodes can act as arbitrators.
Both MGM nodes and SQL nodes can be arbitrators. A value of
0 means that the given node is never used as an arbitrator,
a value of 1 gives the node high priority as an arbitrator,
and a value of 2 gives it low priority. A normal
configuration uses the management server as arbitrator,
setting its ArbitrationRank
to 1 (the
default) and those for all SQL nodes to 0.
Setting this parameter to any other value than 0 (the default) means that responses by the arbitrator to arbitration requests will be delayed by the stated number of milliseconds. It is usually not necessary to change this value.
For queries that are translated into full table scans or
range scans on indexes, it is important for best performance
to fetch records in properly sized batches. It is possible
to set the proper size both in terms of number of records
(BatchSize
) and in terms of bytes
(BatchByteSize
). The actual batch size is
limited by both parameters.
The speed at which queries are performed can vary by more than 40% depending upon how this parameter is set. In future releases, MySQL Server will make educated guesses on how to set parameters relating to batch size, based on the query type.
This parameter is measured in bytes and by default is equal to 32KB.
This parameter is measured in number of records and is by default set to 64. The maximum size is 992.
The batch size is the size of each batch sent from each data node. Most scans are performed in parallel to protect the MySQL Server from receiving too much data from many nodes in parallel; this parameter sets a limit to the total batch size over all nodes.
The default value of this parameter is set to 256KB. Its maximum size is 16MB.
You can obtain some information from a MySQL server running as a
Cluster SQL node using SHOW STATUS
in the
mysql
client, as shown here:
mysql> SHOW STATUS LIKE 'ndb%';
+-----------------------------+---------------+
| Variable_name | Value |
+-----------------------------+---------------+
| Ndb_cluster_node_id | 5 |
| Ndb_config_from_host | 192.168.0.112 |
| Ndb_config_from_port | 1186 |
| Ndb_number_of_storage_nodes | 4 |
+-----------------------------+---------------+
4 rows in set (0.02 sec)
For information about these Cluster system status variables, see Section 5.1.5, “Status Variables”.
TCP/IP is the default transport mechanism for establishing
connections in MySQL Cluster. It is normally not necessary to
define connections because Cluster automatically set ups a
connection between each of the data nodes, between each data
node and all MySQL server nodes, and between each data node and
the management server. (For one exception to this rule, see
Section 16.3.4.8, “TCP/IP Connections Using Direct Connections”.)
[tcp]
sections in the
config.ini
file explicitly define TCP/IP
connections between nodes in the cluster.
It is necessary to define a connection only to override the
default connection parameters. In that case, it is necessary to
define at least NodeId1
,
NodeId2
, and the parameters to change.
Any [tcp]
sections in the
config.ini
file should be listed last,
following any other sections in the file. This is not required
for a [tcp default]
section. This is a
known issue with the way in which the
config.ini
file is read by the cluster
management server.
It is also possible to change the default values for these
parameters by setting them in the [tcp
default]
section.
To identify a connection between two nodes it is necessary
to provide their node IDs in the [tcp]
section of the configuration file. These are the same unique
Id
values for each of these nodes as
described in Section 16.3.4.6, “Defining SQL and Other API Nodes”.
TCP transporters use a buffer to store all messages before performing the send call to the operating system. When this buffer reaches 64KB its contents are sent; these are also sent when a round of messages have been executed. To handle temporary overload situations it is also possible to define a bigger send buffer.
The default size of the send buffer is 256 KB; 2MB is recommended in most situations in which it is necessary to set this parameter. The minimum size is 64 KB; the theoretical maximum is 4 GB.
To be able to retrace a distributed message datagram, it is
necessary to identify each message. When this parameter is
set to Y
, message IDs are transported
over the network. This feature is disabled by default in
production builds, and enabled in -debug
builds.
This parameter is a boolean parameter (enabled by setting it
to Y
or 1
, disabled by
setting it to N
or 0
).
It is disabled by default. When it is enabled, checksums for
all messages are calculated before they placed in the send
buffer. This feature ensures that messages are not corrupted
while waiting in the send buffer, or by the transport
mechanism.
This formerly specified the port number to be used for listening for connections from other nodes. This parameter should no longer be used.
Specifies the size of the buffer used when receiving data from the TCP/IP socket.
The default value of this parameter from its of 64 KB; 1M is recommended in most situations where the size of the receive buffer needs to be set. The minimum possible value is 16K; the theoretical maximum is 4G.
Setting up a cluster using direct connections between data nodes
requires specifying explicitly the crossover IP addresses of the
data nodes so connected in the [tcp]
section
of the cluster config.ini
file.
In the following example, we envision a cluster with at least
four hosts, one each for a management server, an SQL node, and
two data nodes. The cluster as a whole resides on the
172.23.72.*
subnet of a LAN. In addition to
the usual network connections, the two data nodes are connected
directly using a standard crossover cable, and communicate with
one another directly using IP addresses in the
1.1.0.*
address range as shown:
# Management Server [ndb_mgmd] Id=1 HostName=172.23.72.20 # SQL Node [mysqld] Id=2 HostName=172.23.72.21 # Data Nodes [ndbd] Id=3 HostName=172.23.72.22 [ndbd] Id=4 HostName=172.23.72.23 # TCP/IP Connections [tcp] NodeId1=3 NodeId2=4 HostName1=1.1.0.1 HostName2=1.1.0.2
The HostName
parameter, where N
N
is an integer, is
used only when specifying direct TCP/IP connections.
The use of direct connections between data nodes can improve the cluster's overall efficiency by allowing the data nodes to bypass an Ethernet device such as a switch, hub, or router, thus cutting down on the cluster's latency. It is important to note that to take the best advantage of direct connections in this fashion with more than two data nodes, you must have a direct connection between each data node and every other data node in the same node group.
MySQL Cluster attempts to use the shared memory transporter and
configure it automatically where possible. (In very early
versions of MySQL Cluster, shared memory segments functioned
only when the server binary was built using
--with-ndb-shm
.) [shm]
sections in the config.ini
file explicitly
define shared-memory connections between nodes in the cluster.
When explicitly defining shared memory as the connection method,
it is necessary to define at least NodeId1
,
NodeId2
and ShmKey
. All
other parameters have default values that should work well in
most cases.
SHM functionality is considered experimental only. It is not officially supported in any MySQL release series up to and including 5.0. This means that you must determine for yourself or by using our free resources (forums, mailing lists) whether it can be made to work correctly in your specific case.
To identify a connection between two nodes it is necessary
to provide node identifiers for each of them, as
NodeId1
and NodeId2
.
When setting up shared memory segments, a node ID, expressed as an integer, is used to identify uniquely the shared memory segment to use for the communication. There is no default value.
Each SHM connection has a shared memory segment where
messages between nodes are placed by the sender and read by
the reader. The size of this segment is defined by
ShmSize
. The default value is 1MB.
To retrace the path of a distributed message, it is
necessary to provide each message with a unique identifier.
Setting this parameter to Y
causes these
message IDs to be transported over the network as well. This
feature is disabled by default in production builds, and
enabled in -debug
builds.
This parameter is a boolean
(Y
/N
) parameter which
is disabled by default. When it is enabled, checksums for
all messages are calculated before being placed in the send
buffer.
This feature prevents messages from being corrupted while waiting in the send buffer. It also serves as a check against data being corrupted during transport.
[sci]
sections in the
config.ini
file explicitly define SCI
(Scalable Coherent Interface) connections between cluster nodes.
Using SCI transporters in MySQL Cluster is supported only when
the MySQL binaries are built using
--with-ndb-sci=
.
The /your/path/to/SCI
path
should point to a directory
that contains at a minimum lib
and
include
directories containing SISCI
libraries and header files. (See
Section 16.11, “Using High-Speed Interconnects with MySQL Cluster” for more
information about SCI.)
In addition, SCI requires specialized hardware.
It is strongly recommended to use SCI Transporters only for communication between ndbd processes. Note also that using SCI Transporters means that the ndbd processes never sleep. For this reason, SCI Transporters should be used only on machines having at least two CPUs dedicated for use by ndbd processes. There should be at least one CPU per ndbd process, with at least one CPU left in reserve to handle operating system activities.
To identify a connection between two nodes it is necessary
to provide node identifiers for each of them, as
NodeId1
and NodeId2
.
This identifies the SCI node ID on the first Cluster node
(identified by NodeId1
).
It is possible to set up SCI Transporters for failover between two SCI cards which then should use separate networks between the nodes. This identifies the node ID and the second SCI card to be used on the first node.
This identifies the SCI node ID on the second Cluster node
(identified by NodeId2
).
When using two SCI cards to provide failover, this parameter identifies the second SCI card to be used on the second node.
Each SCI transporter has a shared memory segment used for communication between the two nodes. Setting the size of this segment to the default value of 1MB should be sufficient for most applications. Using a smaller value can lead to problems when performing many parallel inserts; if the shared buffer is too small, this can also result in a crash of the ndbd process.
A small buffer in front of the SCI media stores messages before transmitting them over the SCI network. By default, this is set to 8KB. Our benchmarks show that performance is best at 64KB but 16KB reaches within a few percent of this, and there was little if any advantage to increasing it beyond 8KB.
To trace a distributed message it is necessary to identify
each message uniquely. When this parameter is set to
Y
, message IDs are transported over the
network. This feature is disabled by default in production
builds, and enabled in -debug
builds.
This parameter is a boolean value, and is disabled by
default. When Checksum
is enabled,
checksums are calculated for all messages before they are
placed in the send buffer. This feature prevents messages
from being corrupted while waiting in the send buffer. It
also serves as a check against data being corrupted during
transport.
The next three sections provide summary tables of MySQL Cluster
configuration parameters used in the
config.ini
file to govern the cluster's
functioning. Each table lists the parameters for one of the
Cluster node process types (ndbd,
ndb_mgmd, and mysqld), and
includes the parameter's type as well as its default, mimimum, and
maximum values as applicable.
It is also stated what type of restart is required (node restart
or system restart) — and whether the restart must be done
with --initial
— to change the value of a
given configuration parameter. This information is provided in
each table's Restart Type column,
which contains one of the values shown in this list:
N
: Node Restart
IN
: Initial Node Restart
S
: System Restart
IS
: Initial System Restart
When performing a node restart or an initial node restart, all of
the cluster's data nodes must be restarted in turn (also referred
to as a rolling restart). It is possible to
update cluster configuration parameters marked
N
or IN
online — that
is, without shutting down the cluster — in this fashion. An
initial node restart requires restarting each
ndbd process with the
--initial
option.
A system restart requires a complete shutdown and restart of the entire cluster. An initial system restart requires taking a backup of the cluster, wiping the cluster filesystem after shutdown, and then restoring from the backup following the restart.
In any cluster restart, all of the cluster's management servers must be restarted in order for them to read the updated configuration parameter values.
Values for numeric cluster parameters can generally be increased without any problems, although it is advisable to do so progressively, making such adjustments in relatively small increments. However, decreasing the values of such parameters — particularly those relating to memory usage and disk space — is not to be undertaken lightly, and it is recommended that you do so only following careful planning and testing. In addition, it is the generally the case that parameters relating to memory and disk usage which can be raised using a simple node restart require an initial node restart to be lowered.
Because some of these parameters can be used for configuring more than one type of cluster node, they may appear in more than one of the tables.
(Note that 4294967039
— which often
appears as a maximum value in these tables — is equal to
232 –
28 – 1
.)
The following table provides information about parameters used
in the [ndbd]
or [ndbd
default]
sections of a config.ini
file for configuring MySQL Cluster data nodes. For detailed
descriptions and other additional information about each of
these parameters, see
Section 16.3.4.5, “Defining Data Nodes”.
Restart Type Column Values
N
: Node Restart
IN
: Initial Node Restart
S
: System Restart
IS
: Initial System Restart
See Section 16.3.5, “Overview of Cluster Configuration Parameters”, for additional explanations of these abbreviations.
Parameter Name | Type/Units | Default Value | Minimum Value | Maximum Value | Restart Type |
ArbitrationTimeout | milliseconds | 1000 | 10 | 4294967039 | N |
BackupDataBufferSize | bytes | 2M | 0 | 4294967039 | N |
BackupDataDir | string |
| N/A | N/A | IN |
BackupLogBufferSize | bytes | 2M | 0 | 4294967039 | N |
BackupMemory | bytes | 4M | 0 | 4294967039 | N |
BackupWriteSize | bytes | 32K | 2K | 4294967039 | N |
BackupMaxWriteSize | bytes | 256K | 2K | 4294967039 | N |
BatchSizePerLocalScan | integer | 64 | 1 | 992 | N |
DataDir | string | /var/lib/mysql-cluster | N/A | N/A | IN |
DataMemory | bytes | 80M | 1M | 1024G (subject to available system RAM and size of
IndexMemory ) | N |
Diskless | true|false (1 |0 ) | 0 | 0 | 1 | IS |
ExecuteOnComputer | integer | ||||
FileSystemPath | string | value specified for DataDir | N/A | N/A | IN |
HeartbeatIntervalDbApi | milliseconds | 1500 | 100 | 4294967039 | N |
HeartbeatIntervalDbDb | milliseconds | 1500 | 10 | 4294967039 | N |
HostName | string | localhost | N/A | N/A | S |
Id | integer | None | 1 | 49 | N |
IndexMemory | bytes | 18M | 1M | 1024G (subject to available system RAM and size of
DataMemory ) | N |
LockPagesInMainMemory | As of MySQL 5.0.36: integer;
previously: true|false
(1 |0 ) | 0 | 0 | 1 | N |
LogLevelCheckpoint | integer | 0 | 0 | 15 | IN |
LogLevelCongestion | integer | 0 | 0 | 15 | N |
LogLevelConnection | integer | 0 | 0 | 15 | N |
LogLevelError | integer | 0 | 0 | 15 | N |
LogLevelInfo | integer | 0 | 0 | 15 | N |
LogLevelNodeRestart | integer | 0 | 0 | 15 | N |
LogLevelShutdown | integer | 0 | 0 | 15 | N |
LogLevelStartup | integer | 1 | 0 | 15 | N |
LogLevelStatistic | integer | 0 | 0 | 15 | N |
LongMessageBuffer | bytes | 1M | 512K | 4294967039 | N |
MaxNoOfAttributes | integer | 1000 | 32 | 4294967039 | N |
MaxNoOfConcurrentIndexOperations | integer | 8K | 0 | 4294967039 | N |
MaxNoOfConcurrentOperations | integer | 32768 | 32 | 4294967039 | N |
MaxNoOfConcurrentScans | integer | 256 | 2 | 500 | N |
MaxNoOfConcurrentTransactions | integer | 4096 | 32 | 4294967039 | N |
MaxNoOfFiredTriggers | integer | 4000 | 0 | 4294967039 | N |
MaxNoOfIndexes
(DEPRECATED — use
MaxNoOfOrderedIndexes or
MaxNoOfUniqueHashIndexes instead) | integer | 128 | 0 | 4294967039 | N |
MaxNoOfLocalOperations | integer | UNDEFINED | 32 | 4294967039 | N |
MaxNoOfLocalScans | integer | UNDEFINED (see
description) | 32 | 4294967039 | N |
MaxNoOfOrderedIndexes | integer | 128 | 0 | 4294967039 | N |
MaxNoOfSavedMessages | integer | 25 | 0 | 4294967039 | N |
MaxNoOfTables | integer | 128 | 8 | 4294967039 | N |
MaxNoOfTriggers | integer | 768 | 0 | 4294967039 | N |
MaxNoOfUniqueHashIndexes | integer | 64 | 0 | 4294967039 | N |
NoOfDiskPagesToDiskAfterRestartACC | integer (number of 8KB pages per 100 milliseconds) | 20 (= 20 * 80KB = 1.6MB/second) | 1 | 4294967039 | N |
NoOfDiskPagesToDiskAfterRestartTUP | integer (number of 8KB pages per 100 milliseconds) | 40 (= 40 * 80KB = 3.2MB/second) | 1 | 4294967039 | N |
NoOfDiskPagesToDiskDuringRestartACC | integer (number of 8KB pages per 100 milliseconds) | 20 (= 20 * 80KB = 1.6MB/second) | 1 | 4294967039 | N |
NoOfDiskPagesToDiskDuringRestartTUP | integer (number of 8KB pages per 100 milliseconds) | 40 (= 40 * 80KB = 3.2MB/second) | 1 | 4294967039 | N |
NoOfFragmentLogFiles | integer | 8 | 1 | 4294967039 | IS |
NoOfReplicas | integer | None | 1 | 4 | IS |
RedoBuffer | bytes | 8M | 1M | 4294967039 | N |
RestartOnErrorInsert
(DEBUG BUILDS ONLY) | true|false (1 |0 ) | 0 | 0 | 1 | N |
ServerPort
(OBSOLETE) | integer | 1186 | 0 | 4294967039 | N |
StartFailureTimeout | milliseconds | 0 | 0 | 4294967039 | N |
StartPartialTimeout | milliseconds | 30000 | 0 | 4294967039 | N |
StartPartitionedTimeout | milliseconds | 60000 | 0 | 4294967039 | N |
StopOnError | true|false (1 |0 ) | 1 | 0 | 1 | N |
TimeBetweenGlobalCheckpoints | milliseconds | 2000 | 10 | 32000 | N |
TimeBetweenInactiveTransactionAbortCheck | milliseconds | 1000 | 1000 | 4294967039 | N |
TimeBetweenLocalCheckpoints | integer (number of 4-byte words as a base-2 logarithm) | 20 (= 4 * 220 = 4MB write
operations) | 0 | 31 | N |
TimeBetweenWatchDogCheck | milliseconds | 4000 | 70 | 4294967039 | N |
TransactionBufferMemory | bytes | 1M | 1K | 4294967039 | N |
TransactionDeadlockDetectionTimeout | milliseconds | 1200 | 50 | 4294967039 | N |
TransactionInactiveTimeout | milliseconds | 0 | 0 | 4294967039 | N |
UndoDataBuffer | bytes | 16M | 1M | 4294967039 | N |
UndoIndexBuffer | bytes | 2M | 1M | 4294967039 | N |
The following table provides information about parameters used
in the [ndb_mgmd]
or [mgm]
sections of a config.ini
file for
configuring MySQL Cluster management nodes. For detailed
descriptions and other additional information about each of
these parameters, see
Section 16.3.4.4, “Defining the Management Server”.
Restart Type Column Values
N
: Node Restart
IN
: Initial Node Restart
S
: System Restart
IS
: Initial System Restart
See Section 16.3.5, “Overview of Cluster Configuration Parameters”, for additional explanations of these abbreviations.
Parameter Name | Type/Units | Default Value | Minimum Value | Maximum Value | Restart Type |
ArbitrationDelay | milliseconds | 0 | 0 | 4294967039 | N |
ArbitrationRank | integer | 1 | 0 | 2 | N |
DataDir | string | ./ (ndb_mgmd directory) | N/A | N/A | IN |
ExecuteOnComputer | integer | ||||
HostName | string | localhost | N/A | N/A | IN |
Id | integer | None | 1 | 63 | IN |
LogDestination | CONSOLE , SYSLOG , or
FILE | FILE (see
Section 16.3.4.4, “Defining the Management Server”) | N/A | N/A | N |
PortNumber | integer | 1186 | 1 | 65535 | S |
The following table provides information about parameters used
in the [SQL]
and [api]
sections of a config.ini
file for
configuring MySQL Cluster SQL nodes and API nodes. For detailed
descriptions and other additional information about each of
these parameters, see
Section 16.3.4.6, “Defining SQL and Other API Nodes”.
For a discussion of MySQL server options for MySQL Cluster, see Section 16.4.2, “MySQL Cluster-Related Command Options for mysqld”; for information about MySQL server system variables relating to MySQL Cluster, see Section 16.4.3, “MySQL Cluster System Variables”.
Restart Type Column Values
N
: Node Restart
IN
: Initial Node Restart
S
: System Restart
IS
: Initial System Restart
See Section 16.3.5, “Overview of Cluster Configuration Parameters”, for additional explanations of these abbreviations.
Parameter Name | Type/Units | Default Value | Minimum Value | Maximum Value | Restart Type |
ArbitrationDelay | milliseconds | 0 | 0 | 4294967039 | N |
ArbitrationRank | integer | 0 | 0 | 2 | N |
BatchByteSize | bytes | 32K | 1K | 1M | N |
BatchSize | integer | 64 | 1 | 992 | N |
ExecuteOnComputer | integer | ||||
HostName | string | none | N/A | N/A | IN |
Id | integer | None | 1 | 63 | IN |
MaxScanBatchSize | bytes | 256K | 32K | 16M | N |
The parameters discussed in
Logging
and Checkpointing and in
Data
Memory, Index Memory, and String Memory that are used to
configure local checkpoints for a MySQL Cluster do not exist in
isolation, but rather are very much interdepedent on each other.
In this section, we illustrate how these parameters —
including DataMemory
,
IndexMemory
,
NoOfDiskPagesToDiskAfterRestartTUP
,
NoOfDiskPagesToDiskAfterRestartACC
, and
NoOfFragmentLogFiles
— relate to one
another in a working Cluster.
In this example, we assume that our application performs the following numbers of types of operations per hour:
50000 selects
15000 inserts
15000 updates
15000 deletes
We also make the following assumptions about the data used in the application:
We are working with a single table having 40 columns.
Each column can hold up to 32 bytes of data.
A typical UPDATE
run by the application
affects the values of 5 columns.
No NULL
values are inserted by the
application.
A good starting point is to determine the amount of time that should elapse between local checkpoints (LCPs). It worth noting that, in the event of a system restart, it takes 40-60 percent of this interval to execute the REDO log — for example, if the time between LCPs is 5 minutes (300 seconds), then it should take 2 to 3 minutes (120 to 180 seconds) for the REDO log to be read.
The maximum amount of data per node can be assumed to be the size
of the DataMemory
parameter. In this example,
we assume that this is 2 GB. The
NoOfDiskPagesToDiskAfterRestartTUP
parameter
represents the amount of data to be checkpointed per unit time
— however, this parameter is actually expressed as the
number of 8K memory pages to be checkpointed per 100 milliseconds.
2 GB per 300 seconds is approximately 6.8 MB per second, or 700 KB
per 100 milliseconds, which works out to roughly 85 pages per 100
milliseconds.
Similarly, we can calculate
NoOfDiskPagesToDiskAfterRestartACC
in terms of
the time for local checkpoints and the amount of memory required
for indexes — that is, the IndexMemory
.
Assuming that we allow 512 MB for indexes, this works out to
approximately 20 8-KB pages per 100 milliseconds for this
parameter.
Next, we need to determine the number of REDO log files required
— that is, fragment log files — the corresponding
parameter being NoOfFragmentLogFiles
. We need
to make sure that there are sufficient REDO log files for keeping
records for at least 3 local checkpoints. In a production setting,
there are always uncertainties — for instance, we cannot be
sure that disks always operate at top speed or with maximum
throughput. For this reason, it is best to err on the side of
caution, so we double our requirement and calculate a number of
fragment log files which should be enough to keep records covering
6 local checkpoints.
It is also important to remember that the disk also handles writes
to the REDO log and UNDO log, so if you find that the amount of
data being written to disk as detemined by the values of
NoOfDiskPagesToDiskAfterRestartACC
and
NoOfDiskPagesToDiskAfterRestartTUP
is
approaching the amount of disk bandwidth available, you may wish
to increase the time between local checkpoints.
Given 5 minutes (300 seconds) per local checkpoint, this means that we need to support writing log records at maximum speed for 6 * 300 = 1800 seconds. The size of a REDO log record is 72 bytes plus 4 bytes per updated column value plus the maximum size of the updated column, and there is one REDO log record for each table record updated in a transaction, on each node where the data reside. Using the numbers of operations set out previously in this section, we derive the following:
50000 select operations per hour yields 0 log records (and
thus 0 bytes), since SELECT
statements are
not recorded in the REDO log.
15000 DELETE
statements per hour is
approximately 5 delete operations per second. (Since we wish
to be conservative in our estimate, we round up here and in
the following calculations.) No columns are updated by
deletes, so these statements consume only 5 operations * 72
bytes per operation = 360 bytes per second.
15000 UPDATE
statements per hour is roughly
the same as 5 updates per second. Each update uses 72 bytes,
plus 4 bytes per column * 5 columns updated, plus 32 bytes per
column * 5 columns — this works out to 72 + 20 + 160 =
252 bytes per operation, and multiplying this by 5 operation
per second yields 1260 bytes per second.
15000 INSERT
statements per hour is
equivalent to 5 insert operations per second. Each insert
requires REDO log space of 72 bytes, plus 4 bytes per record *
40 columns, plus 32 bytes per column * 40 columns, which is 72
+ 160 + 1280 = 1512 bytes per operation. This times 5
operations per second yields 7560 bytes per second.
So the total number of REDO log bytes being written per second is
approximately 0 + 360 + 1260 + 7560 = 9180 bytes. Multiplied by
1800 seconds, this yields 16524000 bytes required for REDO
logging, or approximately 15.75 MB. The unit used for
NoOfFragmentLogFiles
represents a set of 4
16-MB log files — that is, 64 MB. Thus, the minimum value
(3) for this parameter is sufficient for the scenario envisioned
in this example, since 3 times 64 = 192 MB, or about 12 times what
is required; the default value of 8 (or 512 MB) is more than ample
in this case.
A copy of each altered table record is kept in the UNDO log. In the scenario discussed above, the UNDO log would not require any more space than what is provided by the default seetings. However, given the size of disks, it is sensible to allocate at least 1 GB for it.
This section provides information about MySQL server options, server and status variables that are specific to MySQL Cluster. For general information on using these, and for other options and variables not specific to MySQL Cluster, see Section 5.1, “The MySQL Server”.
For MySQL Cluster configuration parameters used in the cluster
confiuration file (usually named config.ini
),
see Section 16.3, “MySQL Cluster Configuration”.
The following table provides a list of the command line options,
server and status variables applicable within
mysqld
when it is running as an SQL node in a
MySQL Cluster. For a table showing all
command line options, server and status variables available for
use with mysqld, see
Section 5.1.1, “Option and Variable Reference”.
Name | Cmd-line | Option file | System Var | Status Var | Var Scope | Dynamic |
---|---|---|---|---|---|---|
engine_condition_pushdown | Y | Y | Y | both | yes | |
Handler_discover | Y | both | no | |||
have_ndbcluster | Y | global | no | |||
ndb_autoincrement_prefetch_sz | Y | Y | Y | both | yes | |
ndb_cache_check_time | Y | Y | Y | global | yes | |
ndbcluster | Y | Y | Y | both | yes | |
Ndb_cluster_node_id | Y | both | no | |||
Ndb_config_from_host | Y | both | no | |||
Ndb_config_from_port | Y | both | no | |||
ndb_force_send | Y | Y | Y | both | yes | |
ndb_index_stat_cache_entries | Y | Y | ||||
ndb_index_stat_enable | Y | Y | ||||
ndb_index_stat_update_freq | Y | Y | ||||
ndb_optimized_node_selection | Y | Y | ||||
ndb_report_thresh_binlog_epoch_slip | Y | Y | ||||
ndb_report_thresh_binlog_mem_usage | Y | Y | ||||
ndb_use_exact_count | Y | both | yes | |||
ndb_use_transactions | Y | Y |
--ndb-connectstring=
connect_string
When using the NDB Cluster
storage engine,
this option specifies the management server that distributes
cluster configuration data. See
Section 16.3.4.2, “The Cluster Connectstring”, for syntax.
The NDB Cluster
storage engine is necessary
for using MySQL Cluster. If a mysqld binary
includes support for the NDB Cluster
storage engine, the engine is disabled by default. Use the
--ndbcluster
option to enable it. Use
--skip-ndbcluster
to explicitly disable the
engine.
Disable the NDB Cluster
storage engine.
This is the default for binaries that were built with
NDB Cluster
storage engine support; the
server allocates memory and other resources for this storage
engine only if the --ndbcluster
option is
given explicitly. See Section 16.3.3, “Quick Test Setup of MySQL Cluster”,
for an example of usage.
This section provides detailed information about MySQL server
system variables that are specific to MySQL Cluster and the
NDB
storage engine. For system variables not
specific to MySQL Cluster, see
Section 5.1.3, “System Variables”. For general information
on using system variables, see
Section 5.1.4, “Using System Variables”.
Version Introduced | 5.0.3 | ||||||
Option Sets Variable | Yes, multi_range_count | ||||||
Variable Name | multi_range_count | ||||||
Variable Scope | Both | ||||||
Dynamic Variable | yes | ||||||
Value Set |
|
The maximum number of ranges to send to a table handler at
once during range selects. The default value is 256. Sending
multiple ranges to a handler at once can improve the
performance of certain selects dramatically. This especially
true for the NDBCluster
table handler,
which needs to send the range requests to all nodes. Sending a
batch of those requests at once reduces communication costs
significantly.
This variable was added in MySQL 5.0.3.
Version Introduced | 5.0.3 | ||||
Option Sets Variable | Yes, engine_condition_pushdown | ||||
Variable Name | engine_condition_pushdown | ||||
Variable Scope | Both | ||||
Dynamic Variable | yes | ||||
Value Set |
| ||||
Value Set |
|
This variable applies to NDB
. By default it
is 0 (OFF
): If you execute a query such as
SELECT * FROM t WHERE mycol = 42
, where
mycol
is a non-indexed column, the query is
executed as a full table scan on every NDB node. Each node
sends every row to the MySQL server, which applies the
WHERE
condition. If
engine_condition_pushdown
is set to 1
(ON
), the condition is “pushed
down” to the storage engine and sent to the NDB nodes.
Each node uses the condition to perform the scan, and only
sends back to the MySQL server the rows that match the
condition.
This variable was added in MySQL 5.0.3. Before that, the
default NDB
behavior is the same as for a
value of OFF
.
YES
if mysqld supports
NDB Cluster
tables.
DISABLED
if
--skip-ndbcluster
is used.
Option Sets Variable | Yes, ndb_autoincrement_prefetch_sz | ||||||
Variable Name | ndb_autoincrement_prefetch_sz | ||||||
Variable Scope | Both | ||||||
Dynamic Variable | yes | ||||||
Value Set |
| ||||||
Value Set |
| ||||||
Value Set |
| ||||||
Value Set |
| ||||||
Value Set |
| ||||||
Value Set |
| ||||||
Value Set |
| ||||||
Value Set |
| ||||||
Value Set |
| ||||||
Value Set |
|
Determines the probability of gaps in an autoincremented
column. Set it to 1
to minimize this.
Setting it to a high value for optimization — makes
inserts faster, but decreases the likelihood that consecutive
autoincrement numbers will be used in a batch of inserts.
Default value: 32
. Minimum value:
1
.
Beginning with MySQL 5.0.56, this variable affects the number
of AUTO_INCREMENT
IDs that are fetched
between statements only. Within a statement, at least 32 IDs
are now obtained at a time. The default value for
ndb_autoincrement_prefetch_sz
is now
1
, to increase the speed of statements
inserting single rows. (Bug#31956)
Option Sets Variable | Yes, ndb_cache_check_time | ||||
Variable Name | ndb_cache_check_time | ||||
Variable Scope | Global | ||||
Dynamic Variable | yes | ||||
Value Set |
|
The number of milliseconds that elapse between checks of MySQL Cluster SQL nodes by the MySQL query cache. Setting this to 0 (the default and minimum value) means that the query cache checks for validation on every query.
The recommended maximum value for this variable is 1000, which means that the check is performed once per second. A larger value means that the check is performed and possibly invalidated due to updates on different SQL nodes less often. It is generally not desirable to set this to a value greater than 2000.
Option Sets Variable | Yes, ndb_force_send | ||||
Variable Name | ndb_force_send | ||||
Variable Scope | Both | ||||
Dynamic Variable | yes | ||||
Value Set |
|
Forces sending of buffers to NDB
immediately, without waiting for other threads. Defaults to
ON
.
Value Set |
|
Sets the granularity of the statistics by determining the
number of starting and ending keys to store in the statistics
memory cache. Zero means no caching takes place; in this case,
the data nodes are always queried directly. Default value:
32
.
Value Set |
|
Use NDB
index statistics in query
optimization. Defaults to ON
.
Value Set |
|
How often to query data nodes instead of the statistics cache.
For example, a value of 20
(the default)
means to direct every 20th query to
the data nodes.
Value Set |
| ||||||
Value Set |
|
Causes an SQL node to use a data node on the same host machine
as transaction coordinator. Enabled by default. Set to
0
or OFF
to disable, in
which case the SQL node uses each data node in the cluster in
succession. When this option is disabled, or if there is no
data node process running on the same host as the SQL node,
the SQL node attempts to use a given data node 8 times before
proceeding to the next one.
ndb_report_thresh_binlog_epoch_slip
Value Set |
|
This is a threshold on the number of epochs to be behind
before reporting binlog status. For example, a value of
3
(the default) means that if the
difference between which epoch has been received from the
storage nodes and which epoch has been applied to the binlog
is 3 or more, a status message will be sent to the cluster
log.
ndb_report_thresh_binlog_mem_usage
Value Set |
|
This is a threshold on the percentage of free memory remaining
before reporting binlog status. For example, a value of
10
(the default) means that if the amount
of available memory for receiving binlog data from the data
nodes falls below 10%, a status message will be sent to the
cluster log.
Variable Name | ndb_use_exact_count | ||||
Variable Scope | Both | ||||
Dynamic Variable | yes | ||||
Value Set |
|
Forces NDB
to use a count of records during
SELECT COUNT(*)
query planning to speed up
this type of query. The default value is
ON
. For faster queries overall, disable
this feature by setting the value of
ndb_use_exact_count
to
OFF
.
Value Set |
|
You can disable NDB
transaction support by
setting this variable's values to OFF
(not
recommended). The default is ON
.
This section provides detailed information about MySQL server
status variables that relate to MySQL Cluster and the
NDB
storage engine. For status variables not
specific to MySQL Cluster, and for general information on using
status variables, see Section 5.1.5, “Status Variables”.
The MySQL server can ask the NDB Cluster
storage engine if it knows about a table with a given name.
This is called discovery. Handler_discover
indicates the number of times that tables have been discovered
via this mechanism.
If the server is acting as a MySQL Cluster node, then the value of this variable its node ID in the cluster.
If the server is not part of a MySQL Cluster, then the value of this variable is 0.
If the server is part of a MySQL Cluster, the value of this variable is the hostname or IP address of the Cluster management server from which it gets its configuration data.
If the server is not part of a MySQL Cluster, then the value of this variable is an empty string.
Prior to MySQL 5.0.23, this variable was named
Ndb_connected_host
.
If the server is part of a MySQL Cluster, the value of this variable is the number of the port through which it is connected to the Cluster management server from which it gets its configuration data.
If the server is not part of a MySQL Cluster, then the value of this variable is 0.
Prior to MySQL 5.0.23, this variable was named
Ndb_connected_port
.
If the server is part of a MySQL Cluster, the value of this variable is the number of data nodes in the cluster.
If the server is not part of a MySQL Cluster, then the value of this variable is 0.
Prior to MySQL 5.0.29, this variable was named
Ndb_number_of_storage_nodes
.
This portion of the MySQL Cluster chapter covers upgrading and downgrading a MySQL Cluster from one MySQL release to another. It discusses different types of Cluster upgrades and downgrades, and provides a Cluster upgrade/downgrade compatibility matrix (see Section 16.5.2, “Cluster Upgrade and Downgrade Compatibility”). You are expected already to be familiar with installing and configuring a MySQL Cluster prior to attempting an upgrade or downgrade. See Section 16.3, “MySQL Cluster Configuration”.
This section remains in development, and continues to be updated and expanded.
This section discusses how to perform a rolling restart of a MySQL Cluster installation, so called because it involves stopping and starting (or restarting) each node in turn, so that the cluster itself remains operational. This is often done as part of a rolling upgrade or rolling downgrade, where high availability of the cluster is mandatory and no downtime of the cluster as a whole is permissible. Where we refer to upgrades, the information provided here also generally applies to downgrades as well.
There are a number of reasons why a rolling restart might be desirable:
Cluster configuration change. To make a change in the cluster's configuration, such as adding an SQL node to the cluster, or setting a configuration parameter to a new value.
Cluster software upgrade/downgrade. To upgrade the cluster to a newer version of the MySQL Cluster software (or to downgrade it to an older version). This is usually referred to as a “rolling upgrade” (or “rolling downgrade”, when reverting to an older version of MySQL Cluster).
Change on node host. To make changes in the hardware or operating system on which one or more cluster nodes are running
Cluster reset. To reset the cluster because it has reached an undesirable state
Freeing of resources.
To allow memory allocated to a table by successive
INSERT
and DELETE
operations to be freed for re-use by other Cluster tables
The process for performing a rolling restart may be generalised as follows:
Stop all cluster management nodes (ndb_mgmd processes), reconfigure them, then restart them
Stop, reconfigure, then restart each cluster data node (ndbd process) in turn
Stop, reconfigure, then restart each cluster SQL node (mysqld process) in turn
The specifics for implementing a particular rolling upgrade depend upon the actual changes being made. A more detailed view of the process is presented here:
In the previous diagram, Stop and
Start steps indicate that the
process must be stopped completely using a shell command (such as
kill on most Unix systems) or the management
client STOP
command, then started again from a
system shell by invoking the ndbd or
ndb_mgmd executable as appropriate.
Restart indicates the process may
be restarted using the ndb_mgm management
client RESTART
command.
When performing an upgrade or downgrade of the cluster software, you must upgrade or downgrade the management nodes first, then the data nodes, and finally the SQL nodes. Doing so in any other order may leave the cluster in an unusable state.
This section provides information regarding Cluster software and table file compatibility between differing versions of the MySQL Server for purposes of performing upgrades and downgrades.
Only compatibility between MySQL versions with regard to
NDB Cluster
is taken into account in this
section, and there are likely other issues to be considered.
As with any other MySQL software upgrade or downgrade,
you are strongly encouraged to review the relevant portions of
the MySQL Manual for the MySQL versions from which and to which
you intend to migrate, before attempting an upgrade or downgrade
of the MySQL Cluster software. See
Section 2.4.17, “Upgrading MySQL”.
The following table shows Cluster upgrade and downgrade compatibility between different versions of the MySQL Server.
Notes:
4.1 Series:
You cannot upgrade directly from 4.1.8 to 4.1.10 (or newer); you must first upgrade from 4.1.8 to 4.1.9, then upgrade to 4.1.10. Similarly, you cannot downgrade directly from 4.1.10 (or newer) to 4.1.8; you must first downgrade from 4.1.10 to 4.1.9, then downgrade from 4.1.9 to 4.1.8.
If you wish to upgrade a MySQL Cluster to 4.1.15, you must upgrade to 4.1.14 first, and you must upgrade to 4.1.15 before upgrading to 4.1.16 or newer.
Cluster downgrades from 4.1.15 to 4.1.14 (or earlier versions) are not supported.
Cluster upgrades from MySQL Server versions previous to 4.1.8
are not supported; when upgrading from these, you must dump
all NDB
tables, install the new version of
the software, and then reload the tables from the dump.
5.0 Series:
MySQL 5.0.2 was the first public release in this series.
Cluster downgrades from MySQL 5.0 to MySQL 4.1 are not supported.
Cluster downgrades from 5.0.12 to 5.0.11 (or earlier) are not supported.
You cannot restore with ndb_restore to a MySQL 5.0 Cluster using a backup made from a Cluster running MySQL 5.1. You must use mysqldump in such cases.
There was no public release for MySQL 5.0.23.
5.1 Series:
MySQL 5.1.3 was the first public release in this series.
You cannot downgrade a MySQL 5.1.6 or later Cluster using Disk Data tables to MySQL 5.1.5 or earlier unless you convert all such tables to in-memory Cluster tables first.
MySQL 5.1.8, MySQL 5.1.10, and MySQL 5.1.13 were not released.
Online cluster upgrades and downgrades between MySQL 5.1.11
(or an earlier version) and 5.1.12 (or a later version) are
not possible due to major changes in the cluster filesystem.
In such cases, you must perform a backup or dump, upgrade (or
downgrade) the software, start each data node with
--initial
, and then restore from the backup
or dump. You can use NDB
backup/restore or
mysqldump for this purpose.
Online downgrades from MySQL 5.1.14 or later to versions previous to 5.1.14 are not supported due to incompatible changes in the cluster system tables.
Online upgrades from MySQL 5.1.17 and earlier to 5.1.18 and
later are not supported for clusters using replication due to
incompatible changes in the
mysql.ndb_apply_status
table. However, it
should not be necessary to shut down the cluster entirely, if
you follow this modified rolling restart procedure:
Stop the management server, update the
ndb_mgmd
binary, then start it again.
For multiple management servers, repeat this step for
each management server in turn.
For each data node in turn: Stop the data node, replace
the ndbd
binary with the new version,
then restart the data node. It is not necessary to use
--initial
when restarting any of the
data nodes.
Stop all SQL nodes. Replace the
mysqld binary with the new version
for all SQL nodes, then restart them. It is not
necessary to start them one at a time, but they must all
be shut down at the same time before starting any of
them again using the 5.1.18 (or later)
mysqld. Otherwise — due to the
fact that mysql.ndb_apply_status
uses
the NDB
storage engine and is thus
shared between all SQL nodes — there may be
conflicts between MySQL servers using the old and new
versions of the table.
You can find more information about the changes to
ndb_apply_status
in the MySQL
5.1 Manual.
Understanding how to manage MySQL Cluster requires a knowledge of four essential processes. In the next few sections of this chapter, we cover the roles played by these processes in a cluster, how to use them, and what startup options are available for each of them:
mysqld is the traditional MySQL server process.
To be used with MySQL Cluster, mysqld needs to
be built with support for the NDB Cluster
storage engine, as it is in the precompiled binaries available
from http://dev.mysql.com/downloads/. If you build MySQL from
source, you must invoke configure with the
--with-ndbcluster
option to enable NDB
Cluster
storage engine support.
If the mysqld binary has been built with
Cluster support, the NDB Cluster
storage engine
is still disabled by default. You can use either of two possible
options to enable this engine:
Use --ndbcluster
as a startup option on the
command line when starting mysqld.
Insert a line containing ndbcluster
in the
[mysqld]
section of your
my.cnf
file.
An easy way to verify that your server is running with the
NDB Cluster
storage engine enabled is to issue
the SHOW ENGINES
statement in the MySQL Monitor
(mysql). You should see the value
YES
as the Support
value in
the row for NDBCLUSTER
. If you see
NO
in this row or if there is no such row
displayed in the output, you are not running an
NDB
-enabled version of MySQL. If you see
DISABLED
in this row, you need to enable it in
either one of the two ways just described.
To read cluster configuration data, the MySQL server requires at a minimum three pieces of information:
The MySQL server's own cluster node ID
The hostname or IP address for the management server (MGM node)
The number of the TCP/IP port on which it can connect to the management server
Node IDs can be allocated dynamically, so it is not strictly necessary to specify them explicitly.
The mysqld parameter
ndb-connectstring
is used to specify the
connectstring either on the command line when starting
mysqld or in my.cnf
. The
connectstring contains the hostname or IP address where the
management server can be found, as well as the TCP/IP port it
uses.
In the following example, ndb_mgmd.mysql.com
is
the host where the management server resides, and the management
server listens for cluster messages on port 1186:
shell> mysqld --ndbcluster --ndb-connectstring=ndb_mgmd.mysql.com:1186
See Section 16.3.4.2, “The Cluster Connectstring”, for more information on connectstrings.
Given this information, the MySQL server will be a full participant in the cluster. (We often refer to a mysqld process running in this manner as an SQL node.) It will be fully aware of all cluster data nodes as well as their status, and will establish connections to all data nodes. In this case, it is able to use any data node as a transaction coordinator and to read and update node data.
You can see in the mysql client whether a MySQL
server is connected to the cluster using SHOW
PROCESSLIST
. If the MySQL server is connected to the
cluster, and you have the PROCESS
privilege,
then the first row of the output is as shown here:
mysql> SHOW PROCESSLIST \G *************************** 1. row *************************** Id: 1 User: system user Host: db: Command: Daemon Time: 1 State: Waiting for event from ndbcluster Info: NULL
To participate in a MySQL Cluster, the mysqld
process must be started with both the
options --ndbcluster
and
--ndb-connectstring
(or their equivalents in
my.cnf
). If mysqld is
started with only the --ndbcluster
option, or
if it is unable to contact the cluster, it is not possible to
work with NDB
tables, nor is it
possible to create any new tables regardless of storage
engine. The latter restriction is a safety measure
intended to prevent the creation of tables having the same names
as NDB
tables while the SQL node is not
connected to the cluster. If you wish to create tables using a
different storage engine while the mysqld
process is not participating in a MySQL Cluster, you must
restart the server without the
--ndbcluster
option.
ndbd is the process that is used to handle all the data in tables using the NDB Cluster storage engine. This is the process that empowers a data node to accomplish distributed transaction handling, node recovery, checkpointing to disk, online backup, and related tasks.
In a MySQL Cluster, a set of ndbd processes cooperate in handling data. These processes can execute on the same computer (host) or on different computers. The correspondences between data nodes and Cluster hosts is completely configurable.
ndbd generates a set of log files which are
placed in the directory specified by
DataDir
in the
config.ini
configuration file.
These log files are listed below.
node_id
is the node's unique
identifier. Note that node_id
represents the node's unique identifier. For example,
ndb_2_error.log
is the error log
generated by the data node whose node ID is
2
.
ndb_
is a file containing records of all crashes which the
referenced ndbd process has
encountered. Each record in this file contains a brief
error string and a reference to a trace file for this
crash. A typical entry in this file might appear as shown
here:
node_id
_error.log
Date/Time: Saturday 30 July 2004 - 00:20:01 Type of error: error Message: Internal program error (failed ndbrequire) Fault ID: 2341 Problem data: DbtupFixAlloc.cpp Object of reference: DBTUP (Line: 173) ProgramName: NDB Kernel ProcessID: 14909 TraceFile: ndb_2_trace.log.2 ***EOM***
Listings of possible ndbd exit codes
and messages generated when a data node process shuts down
prematurely can be found in
ndbd
Error Messages.
The last entry in the error log file is not
necessarily the newest one (nor is it likely
to be). Entries in the error log are
not listed in chronological order;
rather, they correspond to the order of the trace files
as determined in the
ndb_
file (see below). Error log entries are thus overwritten
in a cyclical and not sequential fashion.
node_id
_trace.log.next
ndb_
is a trace file describing exactly what happened just
before the error occurred. This information is useful for
analysis by the MySQL Cluster development team.
node_id
_trace.log.trace_id
It is possible to configure the number of these trace
files that will be created before old files are
overwritten. trace_id
is a
number which is incremented for each successive trace
file.
ndb_
is the file that keeps track of the next trace file number
to be assigned.
node_id
_trace.log.next
ndb_
is a file containing any data output by the
ndbd process. This file is created only
if ndbd is started as a daemon, which
is the default behavior.
node_id
_out.log
ndb_
is a file containing the process ID of the
ndbd process when started as a daemon.
It also functions as a lock file to avoid the starting of
nodes with the same identifier.
node_id
.pid
ndb_
is a file used only in debug versions of
ndbd, where it is possible to trace all
incoming, outgoing, and internal messages with their data
in the ndbd process.
node_id
_signal.log
It is recommended not to use a directory mounted through NFS
because in some environments this can cause problems whereby
the lock on the .pid
file remains in
effect even after the process has terminated.
To start ndbd, it may also be necessary to specify the hostname of the management server and the port on which it is listening. Optionally, one may also specify the node ID that the process is to use.
shell> ndbd --connect-string="nodeid=2;host=ndb_mgmd.mysql.com:1186"
See Section 16.3.4.2, “The Cluster Connectstring”, for additional information about this issue. Section 16.6.5, “Command Options for MySQL Cluster Processes”, describes other options for ndbd.
When ndbd starts, it actually initiates two processes. The first of these is called the “angel process”; its only job is to discover when the execution process has been completed, and then to restart the ndbd process if it is configured to do so. Thus, if you attempt to kill ndbd via the Unix kill command, it is necessary to kill both processes, beginning with the angel process. The preferred method of terminating an ndbd process is to use the management client and stop the process from there.
The execution process uses one thread for reading, writing, and scanning data, as well as all other activities. This thread is implemented asynchronously so that it can easily handle thousands of concurrent activites. In addition, a watch-dog thread supervises the execution thread to make sure that it does not hang in an endless loop. A pool of threads handles file I/O, with each thread able to handle one open file. Threads can also be used for transporter connections by the transporters in the ndbd process. In a multi-processor system performing a large number of operations (including updates), the ndbd process can consume up to 2 CPUs if permitted to do so.
For a machine with many CPUs it is possible to use several ndbd processes which belong to different node groups; however, such a configuration is still considered experimental and is not supported for MySQL 5.0 in a production setting. See Section 16.12, “Known Limitations of MySQL Cluster”.
The management server is the process that reads the cluster configuration file and distributes this information to all nodes in the cluster that request it. It also maintains a log of cluster activities. Management clients can connect to the management server and check the cluster's status.
It is not strictly necessary to specify a connectstring when starting the management server. However, if you are using more than one management server, a connectstring should be provided and each node in the cluster should specify its node ID explicitly.
See Section 16.3.4.2, “The Cluster Connectstring”, for information about using connectstrings. Section 16.6.5, “Command Options for MySQL Cluster Processes”, describes other options for ndb_mgmd.
The following files are created or used by
ndb_mgmd in its starting directory, and are
placed in the DataDir
as specified in the
config.ini
configuration file. In the
list that follows, node_id
is the
unique node identifier.
config.ini
is the configuration file
for the cluster as a whole. This file is created by the
user and read by the management server.
Section 16.3, “MySQL Cluster Configuration”, discusses
how to set up this file.
ndb_
is the cluster events log file. Examples of such events
include checkpoint startup and completion, node startup
events, node failures, and levels of memory usage. A
complete listing of cluster events with descriptions may
be found in Section 16.7, “Management of MySQL Cluster”.
node_id
_cluster.log
When the size of the cluster log reaches one million
bytes, the file is renamed to
ndb_
,
where node_id
_cluster.log.seq_id
seq_id
is the sequence
number of the cluster log file. (For example: If files
with the sequence numbers 1, 2, and 3 already exist, the
next log file is named using the number
4
.)
ndb_
is the file used for node_id
_out.logstdout
and
stderr
when running the management
server as a daemon.
ndb_
is the process ID file used when running the management
server as a daemon.
node_id
.pid
The ndb_mgm management client process is actually not needed to run the cluster. Its value lies in providing a set of commands for checking the cluster's status, starting backups, and performing other administrative functions. The management client accesses the management server using a C API. Advanced users can also employ this API for programming dedicated management processes to perform tasks similar to those performed by ndb_mgm.
To start the management client, it is necessary to supply the hostname and port number of the management server:
shell> ndb_mgm [host_name
[port_num
]]
For example:
shell> ndb_mgm ndb_mgmd.mysql.com 1186
The default hostname and port number are
localhost
and 1186, respectively.
Additional information about using ndb_mgm can be found in Section 16.6.5.3, “Command Options for ndb_mgm”, and Section 16.7.2, “Commands in the MySQL Cluster Management Client”.
All MySQL Cluster executables (except for
mysqld) take the options described in this
section. Users of earlier MySQL Cluster versions should note that
some of these options have been changed to make them consistent
with one another as well as with mysqld. You
can use the --help
option with any MySQL Cluster
executable to view a list of the options which it supports.
The following options are common to all MySQL Cluster executables:
--help
--usage
,
-?
Prints a short list with descriptions of the available command options.
--connect-string=
,
connect_string
-c
connect_string
connect_string
sets the
connectstring to the management server as a command option.
shell> ndbd --connect-string="nodeid=2;host=ndb_mgmd.mysql.com:1186"
For more information, see Section 16.3.4.2, “The Cluster Connectstring”.
--debug[=
options
]
This option can be used only for versions compiled with debugging enabled. It is used to enable output from debug calls in the same manner as for the mysqld process.
--execute=
,
command
-e
command
Can be used to send a command to a Cluster executable from the system shell. For example, either of the following:
shell> ndb_mgm -e "SHOW"
or
shell> ndb_mgm --execute="SHOW"
is equivalent to
ndb_mgm> SHOW
This is analogous to how the --execute
or
-e
option works with the
mysql command-line client. See
Section 4.2.2.1, “Using Options on the Command Line”.
--version
, -V
Prints the MySQL Cluster version number of the executable. The version number is relevant because not all versions can be used together, and the MySQL Cluster startup process verifies that the versions of the binaries being used can co-exist in the same cluster. This is also important when performing an online (rolling) software upgrade or downgrade of MySQL Cluster. (See Section 16.5.1, “Performing a Rolling Restart of the Cluster”).
The next few sections describe options specific to individual
NDB
programs.
See Section 16.4.2, “MySQL Cluster-Related Command Options for mysqld”, for mysqld options relating to MySQL Cluster.
For options common to all NDB
programs, see
Section 16.6.5, “Command Options for MySQL Cluster Processes”.
--bind-address
Causes ndbd to bind to a specific network interface. This option has no default value.
This option was added in MySQL 5.0.29.
--daemon
, -d
Instructs ndbd to execute as a daemon
process. This is the default behavior.
--nodaemon
can be used to prevent the
process from running as a daemon.
--initial
Instructs ndbd to perform an initial start. An initial start erases any files created for recovery purposes by earlier instances of ndbd. It also re-creates recovery log files. Note that on some operating systems this process can take a substantial amount of time.
An --initial
start is to be used
only when starting the
ndbd process under very special
circumstances; this is because this option causes all files
to be removed from the Cluster filesystem and all redo log
files to be re-created. These circumstances are listed here:
When performing a software upgrade which has changed the contents of any files.
When restarting the node with a new version of ndbd.
As a measure of last resort when for some reason the node restart or system restart repeatedly fails. In this case, be aware that this node can no longer be used to restore data due to the destruction of the data files.
This option does not affect any backup files that have already been created by the affected node.
It is permissible to use this option when starting the cluster for the very first time (that is, before any data node files have been created); however, it is not necessary to do so.
--initial-start
This option is used when performing a partial initial start
of the cluster. Each node should be started with this
option, as well as --nowait-nodes
.
For example, suppose you have a 4-node cluster whose data nodes have the IDs 2, 3, 4, and 5, and you wish to perform a partial initial start using only nodes 2, 4, and 5 — that is, omitting node 3:
ndbd --ndbd-nodeid=2 --nowait-nodes=3 --initial-start ndbd --ndbd-nodeid=4 --nowait-nodes=3 --initial-start ndbd --ndbd-nodeid=5 --nowait-nodes=3 --initial-start
This option was added in MySQL 5.0.21.
--nowait-nodes=
node_id_1
[,
node_id_2
[, ...]]
This option takes a list of data nodes which for which the cluster will not wait for before starting.
This can be used to start the cluster in a partitioned
state. For example, to start the cluster with only half of
the data nodes (nodes 2, 3, 4, and 5) running in a 4-node
cluster, you can start each ndbd process
with --nowait-nodes=3,5
. In this case, the
cluster starts as soon as nodes 2 and 4 connect, and does
not wait
StartPartitionedTimeout
milliseconds for
nodes 3 and 5 to connect as it would otherwise.
If you wanted to start up the same cluster as in the
previous example without one ndbd —
say, for example, that the host machine for node 3 has
suffered a hardware failure — then start nodes 2, 4,
and 5 with --nowait-nodes=3
. Then the
cluster will start as soon as nodes 2, 4, and 5 connect and
will not wait for node 3 to start.
This option was added in MySQL 5.0.21.
--nodaemon
Instructs ndbd not to start as a daemon process. This is useful when ndbd is being debugged and you want output to be redirected to the screen.
--nostart
, -n
Instructs ndbd not to start
automatically. When this option is used,
ndbd connects to the management server,
obtains configuration data from it, and initializes
communication objects. However, it does not actually start
the execution engine until specifically requested to do so
by the management server. This can be accomplished by
issuing the proper START
command in the
management client (see
Section 16.7.2, “Commands in the MySQL Cluster Management Client”).
For options common to NDB programs, see Section 16.6.5, “Command Options for MySQL Cluster Processes”.
--config-file=
,
filename
-f
filename
Instructs the management server as to which file it should
use for its configuration file. By default, the management
server looks for a file named
config.ini
in the same directory as the
ndb_mgmd executable; otherwise the
filename and location must be specified explicitly.
This option also can be given as -c
, but this
shortcut is obsolete and should not
be used in new installations.
file_name
--daemon
, -d
Instructs ndb_mgmd to start as a daemon process. This is the default behavior.
--nodaemon
Instructs ndb_mgmd not to start as a daemon process.
--print-full-config
, -P
Shows extended information regarding the configuration of
the cluster. With this option on the command line the
ndb_mgmd process prints information about
the cluster setup including an extensive list of the cluster
configuration sections as well as parameters and their
values. Normally used together with the
--config-file
(-f
) option.
For options common to NDB programs, see Section 16.6.5, “Command Options for MySQL Cluster Processes”.
--try-reconnect=
number
If the connection to the management server is broken, the
node tries to reconnect to it every 5 seconds until it
succeeds. By using this option, it is possible to limit the
number of attempts to number
before giving up and reporting an error instead.
Managing a MySQL Cluster involves a number of tasks, the first of which is to configure and start MySQL Cluster. This is covered in Section 16.3, “MySQL Cluster Configuration”, and Section 16.6, “Process Management in MySQL Cluster”.
The following sections cover the management of a running MySQL Cluster.
For information about security issues relating to management and deployment of a MySQL Cluster, see Section 16.8, “MySQL Cluster Security Issues”.
There are essentially two methods of actively managing a running
MySQL Cluster. The first of these is through the use of commands
entered into the management client whereby cluster status can be
checked, log levels changed, backups started and stopped, and nodes
stopped and started. The second method involves studying the
contents of the cluster log
ndb_
;
this is usually found in the management server's
node_id
_cluster.logDataDir
directory, but this location can be
overridden using the LogDestination
option
— see Section 16.3.4.4, “Defining the Management Server”, for
details. (Recall that node_id
represents
the unique identifier of the node whose activity is being logged.)
The cluster log contains event reports generated by
ndbd. It is also possible to send cluster log
entries to a Unix system log.
In addition, some aspects of the cluster's operation can be
monitored from an SQL node using the SHOW ENGINE NDB
STATUS
statement. See Section 12.5.4.9, “SHOW ENGINE
Syntax”, for
more information.
This section provides a simplified outline of the steps involved when MySQL Cluster data nodes are started. More complete information can be found in MySQL Cluster Start Phases.
These phases are the same as those reported in the output from the
command in the management client. (See
Section 16.7.2, “Commands in the MySQL Cluster Management Client”, for more
information about this command.)
node_id
STATUS
Start types. There are several different startup types and modes, as shown here:
Initial Start.
The cluster starts with a clean filesystem on all data
nodes. This occurs either when the cluster started for
the very first time, or when all data nodes are
restarted using the --initial
option.
Disk Data files are not removed when restarting a
node using --initial
.
System Restart. The cluster starts and reads data stored in the data nodes. This occurs when the cluster has been shut down after having been in use, when it is desired for the cluster to resume operations from the point where it left off.
Node Restart. This is the online restart of a cluster node while the cluster itself is running.
Initial Node Restart. This is the same as a node restart, except that the node is reinitialized and started with a clean filesystem.
Setup and initialization (Phase -1). Prior to startup, each data node (ndbd process) must be initialized. Initialization consists of the following steps:
Obtain a node ID
Fetch configuration data
Allocate ports to be used for inter-node communications
Allocate memory according to settings obtained from the configuration file
When a data node or SQL node first connects to the management node, it reserves a cluster node ID. To make sure that no other node allocates the same node ID, this ID is retained until the node has managed to connect to the cluster and at least one ndbd reports that this node is connected. This retention of the node ID is guarded by the connection between the node in question and ndb_mgmd.
Normally, in the event of a problem with the node, the node disconnects from the management server, the socket used for the connection is closed, and the reserved node ID is freed. However, if a node is disconnected abruptly — for example, due to a hardware failure in one of the cluster hosts, or because of network issues — the normal closing of the socket by the operating system may not take place. In this case, the node ID continues to be reserved and not released until a TCP timeout occurs 10 or so minutes later.
To take care of this problem, you can use PURGE STALE
SESSIONS
. Running this statement forces all reserved
node IDs to be checked; any that are not being used by nodes
actually connected to the cluster are then freed.
Beginning with MySQL 5.1.11, timeout handling of node ID
assignments is implemented. This performs the ID usage checks
automatically after approximately 20 seconds, so that
PURGE STALE SESSIONS
should no longer be
necessary in a normal Cluster start.
After each data node has been initialized, the cluster startup process can proceed. The stages which the cluster goes through during this process are listed here:
Phase 0.
The NDBFS
and
NDBCNTR
blocks start (see
NDB
Kernel Blocks). The
cluster filesystem is cleared, if the cluster was started
with the --initial
option.
Phase 1.
In this stage, all remaining NDB
kernel
blocks are started. Cluster connections are set up,
inter-block communications are established, and Cluster
heartbeats are started. In the case of a node restart, API
node connections are also checked.
When one or more nodes hang in Phase 1 while the remaining node or nodes hang in Phase 2, this often indicates network problems. One possible cause of such issues is one or more cluster hosts having multiple network interfaces. Another common source of problems causing this condition is the blocking of TCP/IP ports needed for communications between cluster nodes. In the latter case, this is often due to a misconfigured firewall.
Phase 2.
The NDBCNTR
kernel block checks the
states of all existing nodes. The master node is chosen,
and the cluster schema file is initialized.
Phase 3.
The DBLQH
and DBTC
kernel blocks set up communications between them. The
startup type is determined; if this is a restart, the
DBDIH
block obtains permission to
perform the restart.
Phase 4.
For an initial start or initial node restart, the redo log
files are created. The number of these files is equal to
NoOfFragmentLogFiles
.
For a system restart:
Read schema or schemas.
Read data from the local checkpoint.
Apply all redo information until the latest restorable global checkpoint has been reached.
For a node restart, find the tail of the redo log.
Phase 5. Most of the database-related portion of a data node start is performed during this phase. For an initial start or system restart, a local checkpoint is executed, followed by a global checkpoint. Periodic checks of memory usage begin during this phase, and any required node takeovers are performed.
Phase 6. In this phase, node groups are defined and set up.
Phase 7.
The arbitrator node is selected and begins to function.
The next backup ID is set, as is the backup disk write
speed. Nodes reaching this start phase are marked as
Started
. It is now possible for API
nodes (including SQL nodes) to connect to the cluster.
connect.
Phase 8.
If this is a system restart, all indexes are rebuilt (by
DBDIH
).
Phase 9. The node internal startup variables are reset.
Phase 100 (OBSOLETE). Formerly, it was at this point during a node restart or initial node restart that API nodes could connect to the node and begin to receive events. Currently, this phase is empty.
Phase 101.
At this point in a node restart or initial node restart,
event delivery is handed over to the node joining the
cluster. The newly-joined node takes over responsibility
for delivering its primary data to subscribers. This phase
is also referred to as SUMA
handover phase.
After this process is completed for an initial start or system restart, transaction handling is enabled. For a node restart or initial node restart, completion of the startup process means that the node may now act as a transaction coordinator.
In addition to the central configuration file, a cluster may also be controlled through a command-line interface available through the management client ndb_mgm. This is the primary administrative interface to a running cluster.
Commands for the event logs are given in Section 16.7.3, “Event Reports Generated in MySQL Cluster”; commands for creating backups and restoring from backup are provided in Section 16.9, “On-line Backup of MySQL Cluster”.
The management client has the following basic commands. In the
listing that follows, node_id
denotes
either a database node ID or the keyword ALL
,
which indicates that the command should be applied to all of the
cluster's data nodes.
HELP
Displays information on all available commands.
SHOW
Displays information on the cluster's status.
In a cluster where multiple management nodes are in use, this command displays information only for data nodes that are actually connected to the current management server.
node_id
START
Brings online the data node identified by
node_id
(or all data nodes).
Beginning with MySQL 5.0.19, this command can also be used to individual management nodes online.
ALL START
continues to affect data
nodes only.
To use this command to bring a data node online, the data node must have been started using ndbd --nostart or ndbd -n.
node_id
STOP
Stops the data node identified by
node_id
(or all data nodes).
Beginning with MySQL 5.0.19, this command can also be used to stop individual management nodes.
ALL STOP
continues to affect data nodes
only.
A node affected by this command disconnects from the cluster, and its associated ndbd or ndb_mgmd process terminates.
node_id
RESTART [-n] [-i]
[-a]
Restarts the data node identified by
node_id
(or all data nodes).
Using the -i
option with
RESTART
causes the data node to perform an
initial restart; that is, the node's filesystem is deleted and
recreated. The effect is the same as that obtained from
stopping the data node process and then starting it again
using ndbd --initial from the system shell.
Using the -n
option causes the data node
process to be restarted, but the data node is not actually
brought online until the appropriate START
command is issued. The effect of this option is the same as
that obtained from stopping the data node and then starting it
again using ndbd --nostart
or ndbd
-n
from the system shell.
Using the -a
causes all current transactions
relying on this node to be aborted. No GCP check is done when
the node rejoins the cluster.
node_id
STATUS
Displays status information for the data node identified by
node_id
(or for all data nodes).
ENTER SINGLE USER MODE
node_id
Enters single user mode, whereby only the MySQL server
identified by the node ID node_id
is allowed to access the database.
Do not attempt to have data nodes join the cluster while it is running in single user mode. Doing so can cause subsequent multiple node failures. Beginning with MySQL 5.0.29, it is no longer possible to add nodes while in single user mode. (See Bug#20395 for more information.)
EXIT SINGLE USER MODE
Exits single user mode, allowing all SQL nodes (that is, all running mysqld processes) to access the database.
QUIT
, EXIT
Terminates the management client.
This command does not affect any nodes connected to the cluster.
SHUTDOWN
Shuts down all cluster data nodes and management nodes. To
exit the management client after this has been done, use
EXIT
or QUIT
.
This command does not shut down any SQL nodes or API nodes that are connected to the cluster.
In this section, we discuss the types of event logs provided by MySQL Cluster, and the types of events that are logged.
MySQL Cluster provides two types of event log:
The cluster log, which includes events generated by all cluster nodes. The cluster log is the log recommended for most uses because it provides logging information for an entire cluster in a single location.
By default, the cluster log is saved to a file named
ndb_
,
(where node_id
_cluster.lognode_id
is the node ID of
the management server) in the same directory where the
ndb_mgm binary resides.
Cluster logging information can also be sent to
stdout
or a syslog
facility in addition to or instead of being saved to a file,
as determined by the values set for the
DataDir
and
LogDestination
configuration parameters.
See Section 16.3.4.4, “Defining the Management Server”, for more
information about these parameters.
Node logs are local to each node.
Output generated by node event logging is written to the file
ndb_
(where node_id
_out.lognode_id
is the node's node
ID) in the node's DataDir
. Node event logs
are generated for both management nodes and data nodes.
Node logs are intended to be used only during application development, or for debugging application code.
Both types of event logs can be set to log different subsets of events.
Each reportable event can be distinguished according to three different criteria:
Category: This can be any one of the
following values: STARTUP
,
SHUTDOWN
, STATISTICS
,
CHECKPOINT
, NODERESTART
,
CONNECTION
, ERROR
, or
INFO
.
Priority: This is represented by one of the numbers from 1 to 15 inclusive, where 1 indicates “most important” and 15 “least important.”
Severity Level: This can be any one of
the following values: ALERT
,
CRITICAL
, ERROR
,
WARNING
, INFO
, or
DEBUG
.
Both the cluster log and the node log can be filtered on these properties.
The format used in the cluster log is as shown here:
2007-01-26 19:35:55 [MgmSrvr] INFO -- Node 1: Data usage is 2%(60 32K pages of total 2560) 2007-01-26 19:35:55 [MgmSrvr] INFO -- Node 1: Index usage is 1%(24 8K pages of total 2336) 2007-01-26 19:35:55 [MgmSrvr] INFO -- Node 1: Resource 0 min: 0 max: 639 curr: 0 2007-01-26 19:35:55 [MgmSrvr] INFO -- Node 2: Data usage is 2%(76 32K pages of total 2560) 2007-01-26 19:35:55 [MgmSrvr] INFO -- Node 2: Index usage is 1%(24 8K pages of total 2336) 2007-01-26 19:35:55 [MgmSrvr] INFO -- Node 2: Resource 0 min: 0 max: 639 curr: 0 2007-01-26 19:35:55 [MgmSrvr] INFO -- Node 3: Data usage is 2%(58 32K pages of total 2560) 2007-01-26 19:35:55 [MgmSrvr] INFO -- Node 3: Index usage is 1%(25 8K pages of total 2336) 2007-01-26 19:35:55 [MgmSrvr] INFO -- Node 3: Resource 0 min: 0 max: 639 curr: 0 2007-01-26 19:35:55 [MgmSrvr] INFO -- Node 4: Data usage is 2%(74 32K pages of total 2560) 2007-01-26 19:35:55 [MgmSrvr] INFO -- Node 4: Index usage is 1%(25 8K pages of total 2336) 2007-01-26 19:35:55 [MgmSrvr] INFO -- Node 4: Resource 0 min: 0 max: 639 curr: 0 2007-01-26 19:39:42 [MgmSrvr] INFO -- Node 4: Node 9 Connected 2007-01-26 19:39:42 [MgmSrvr] INFO -- Node 1: Node 9 Connected 2007-01-26 19:39:42 [MgmSrvr] INFO -- Node 1: Node 9: API version 5.1.15 2007-01-26 19:39:42 [MgmSrvr] INFO -- Node 2: Node 9 Connected 2007-01-26 19:39:42 [MgmSrvr] INFO -- Node 2: Node 9: API version 5.1.15 2007-01-26 19:39:42 [MgmSrvr] INFO -- Node 3: Node 9 Connected 2007-01-26 19:39:42 [MgmSrvr] INFO -- Node 3: Node 9: API version 5.1.15 2007-01-26 19:39:42 [MgmSrvr] INFO -- Node 4: Node 9: API version 5.1.15 2007-01-26 19:59:22 [MgmSrvr] ALERT -- Node 2: Node 7 Disconnected 2007-01-26 19:59:22 [MgmSrvr] ALERT -- Node 2: Node 7 Disconnected
Each line in the cluster log contains the following information:
A timestamp in
format.
YYYY
-MM
-DD
HH
:MM
:SS
The type of node which is performing the logging. In the
cluster log, this is always [MgmSrvr]
.
The severity of the event.
The ID of the node reporting the event.
A description of the event. The most common types of events to appear in the log are connections and disconnections between different nodes in the cluster, and when checkpoints occur. In some cases, the description may contain status information.
The following management commands are related to the cluster log:
CLUSTERLOG ON
Turns the cluster log on.
CLUSTERLOG OFF
Turns the cluster log off.
CLUSTERLOG INFO
Provides information about cluster log settings.
node_id
CLUSTERLOG
category
=threshold
Logs category
events with
priority less than or equal to
threshold
in the cluster log.
CLUSTERLOG FILTER
severity_level
Toggles cluster logging of events of the specified
severity_level
.
The following table describes the default setting (for all data nodes) of the cluster log category threshold. If an event has a priority with a value lower than or equal to the priority threshold, it is reported in the cluster log.
Note that events are reported per data node, and that the threshold can be set to different values on different nodes.
Category | Default threshold (All data nodes) |
STARTUP | 7 |
SHUTDOWN | 7 |
STATISTICS | 7 |
CHECKPOINT | 7 |
NODERESTART | 7 |
CONNECTION | 7 |
ERROR | 15 |
INFO | 7 |
The STATISTICS
category can provide a great
deal of useful data. See
Section 16.7.3.3, “Using CLUSTERLOG STATISTICS
”, for more
information.
Thresholds are used to filter events within each category. For
example, a STARTUP
event with a priority of 3
is not logged unless the threshold for
STARTUP
is set to 3 or higher. Only events
with priority 3 or lower are sent if the threshold is 3.
The following table shows the event severity levels.
These correspond to Unix syslog
levels,
except for LOG_EMERG
and
LOG_NOTICE
, which are not used or mapped.
1 | ALERT | A condition that should be corrected immediately, such as a corrupted system database |
2 | CRITICAL | Critical conditions, such as device errors or insufficient resources |
3 | ERROR | Conditions that should be corrected, such as configuration errors |
4 | WARNING | Conditions that are not errors, but that might require special handling |
5 | INFO | Informational messages |
6 | DEBUG | Debugging messages used for NDB Cluster development |
Event severity levels can be turned on or off (using
CLUSTERLOG FILTER
— see above). If a
severity level is turned on, then all events with a priority
less than or equal to the category thresholds are logged. If the
severity level is turned off then no events belonging to that
severity level are logged.
Cluster log levels are set on a per
ndb_mgmd, per subscriber basis. This means
that, in a MySQL Cluster with multiple management servers,
using a CLUSTERLOG
command in an instance
of ndb_mgm connected to one management
server affects only logs generated by that management server
but not by any of the others. This also means that, should one
of the management servers be restarted, only logs generated by
that management server are affected by the resetting of log
levels caused by the restart.
An event report reported in the event logs has the following format:
datetime
[string
]severity
--message
For example:
09:19:30 2005-07-24 [NDB] INFO -- Node 4 Start phase 4 completed
This section discusses all reportable events, ordered by category and severity level within each category.
In the event descriptions, GCP and LCP mean “Global Checkpoint” and “Local Checkpoint”, respectively.
CONNECTION
Events
These events are associated with connections between Cluster nodes.
Event | Priority | Severity Level | Description |
data nodes connected | 8 | INFO | Data nodes connected |
data nodes disconnected | 8 | INFO | Data nodes disconnected |
Communication closed | 8 | INFO | SQL node or data node connection closed |
Communication opened | 8 | INFO | SQL node or data node connection opened |
CHECKPOINT
Events
The logging messages shown here are associated with checkpoints.
Event | Priority | Severity Level | Description |
LCP stopped in calc keep GCI | 0 | ALERT | LCP stopped |
Local checkpoint fragment completed | 11 | INFO | LCP on a fragment has been completed |
Global checkpoint completed | 10 | INFO | GCP finished |
Global checkpoint started | 9 | INFO | Start of GCP: REDO log is written to disk |
Local checkpoint completed | 8 | INFO | LCP completed normally |
Local checkpoint started | 7 | INFO | Start of LCP: data written to disk |
Report undo log blocked | 7 | INFO | UNDO logging blocked; buffer near overflow |
STARTUP
Events
The following events are generated in response to the startup of a node or of the cluster and of its success or failure. They also provide information relating to the progress of the startup process, including information concerning logging activities.
Event | Priority | Severity Level | Description |
Internal start signal received STTORRY | 15 | INFO | Blocks received after completion of restart |
Undo records executed | 15 | INFO | |
New REDO log started | 10 | INFO | GCI keep X , newest restorable GCI
Y |
New log started | 10 | INFO | Log part X , start MB
Y , stop MB
Z |
Node has been refused for inclusion in the cluster | 8 | INFO | Node cannot be included in cluster due to misconfiguration, inability to establish communication, or other problem |
data node neighbors | 8 | INFO | Shows neighboring data nodes |
data node start phase X completed | 4 | INFO | A data node start phase has been completed |
Node has been successfully included into the cluster | 3 | INFO | Displays the node, managing node, and dynamic ID |
data node start phases initiated | 1 | INFO | NDB Cluster nodes starting |
data node all start phases completed | 1 | INFO | NDB Cluster nodes started |
data node shutdown initiated | 1 | INFO | Shutdown of data node has commenced |
data node shutdown aborted | 1 | INFO | Unable to shut down data node normally |
NODERESTART
Events
The following events are generated when restarting a node and relate to the success or failure of the node restart process.
Event | Priority | Severity Level | Description |
Node failure phase completed | 8 | ALERT | Reports completion of node failure phases |
Node has failed, node state was X | 8 | ALERT | Reports that a node has failed |
Report arbitrator results | 2 | ALERT | There are eight different possible results for arbitration attempts:
|
Completed copying a fragment | 10 | INFO | |
Completed copying of dictionary information | 8 | INFO | |
Completed copying distribution information | 8 | INFO | |
Starting to copy fragments | 8 | INFO | |
Completed copying all fragments | 8 | INFO | |
GCP takeover started | 7 | INFO | |
GCP takeover completed | 7 | INFO | |
LCP takeover started | 7 | INFO | |
LCP takeover completed (state = X ) | 7 | INFO | |
Report whether an arbitrator is found or not | 6 | INFO | There are seven different possible outcomes when seeking an arbitrator:
|
STATISTICS
Events
The following events are of a statistical nature. They provide information such as numbers of transactions and other operations, amount of data sent or received by individual nodes, and memory usage.
Event | Priority | Severity Level | Description |
Report job scheduling statistics | 9 | INFO | Mean internal job scheduling statistics |
Sent number of bytes | 9 | INFO | Mean number of bytes sent to node X |
Received # of bytes | 9 | INFO | Mean number of bytes received from node X |
Report transaction statistics | 8 | INFO | Numbers of: transactions, commits, reads, simple reads, writes, concurrent operations, attribute information, and aborts |
Report operations | 8 | INFO | Number of operations |
Report table create | 7 | INFO | |
Memory usage | 5 | INFO | Data and index memory usage (80%, 90%, and 100%) |
ERROR
Events
These events relate to Cluster errors and warnings. The presence of one or more of these generally indicates that a major malfunction or failure has occurred.
Event | Priority | Severity | Description |
Dead due to missed heartbeat | 8 | ALERT | Node X declared “dead” due to
missed heartbeat |
Transporter errors | 2 | ERROR | |
Transporter warnings | 8 | WARNING | |
Missed heartbeats | 8 | WARNING | Node X missed heartbeat
#Y |
General warning events | 2 | WARNING |
INFO
Events
These events provide general information about the state of the cluster and activities associated with Cluster maintenance, such as logging and heartbeat transmission.
Event | Priority | Severity | Description |
Sent heartbeat | 12 | INFO | Heartbeat sent to node X |
Create log bytes | 11 | INFO | Log part, log file, MB |
General information events | 2 | INFO |
The NDB
management client's
CLUSTERLOG STATISTICS
command can provide a
number of useful statistics in its output. The following
statistics are reported by the transaction coordinator:
Statistic | Description (Number of...) |
Trans. Count | Transactions attempted with this node as coordinator |
Commit Count | Transactions committed with this node as coordinator |
Read Count | Primary key reads (all) |
Simple Read Count | Primary key reads reading the latest committed value |
Write Count | Primary key writes (includes all INSERT ,
UPDATE , and DELETE
operations) |
AttrInfoCount | Data words used to describe all reads and writes received |
Concurrent Operations | All concurrent operations ongoing at the moment the report is taken |
Abort Count | Transactions with this node as coordinator that were aborted |
Scans | Scans (all) |
Range Scans | Index scans |
The ndbd process has a scheduler that runs in an infinite loop. During each loop scheduler performs the following tasks:
Read any incoming messages from sockets into a job buffer.
Check whether there are any timed messages to be executed; if so, put these into the job buffer as well.
Execute (in a loop) any messages in the job buffer.
Send any distributed messages that were generated by executing the messages in the job buffer.
Wait for any new incoming messages.
The number of loops executed in the third step is reported as
the Mean Loop Counter
. This statistic
increases in size as the utilisation of the TCP/IP buffer
improves. You can use this to monitor performance as you add new
processes to the cluster.
The Mean send size
and Mean receive
size
statistics allow you to gauge the efficiency of
writes and reads (respectively) between nodes. These values are
given in bytes. Higher values mean a lower cost per byte sent or
received; the maximum is 64k.
To cause all cluster log statistics to be logged, you can use
the following command in the NDB
management
client:
ndb_mgm> ALL CLUSTERLOG STATISTICS=15
Setting the threshold for STATISTICS
to 15
causes the cluster log to become very verbose, and to gow
quite rapidly in size, in direct proportion to the number of
cluster nodes and the amount of activity on the cluster.
Single user mode allows the database administrator to restrict access to the database system to a single API node, such as a MySQL server (SQL node) or an instance of ndb_restore. When entering single user mode, connections to all other API nodes are closed gracefully and all running transactions are aborted. No new transactions are permitted to start.
Once the cluster has entered single user mode, only the designated API node is granted access to the database.
You can use the ALL STATUS command to see when the cluster has entered single user mode.
Example:
ndb_mgm> ENTER SINGLE USER MODE 5
After this command has executed and the cluster has entered single
user mode, the API node whose node ID is 5
becomes the cluster's only permitted user.
The node specified in the preceding command must be an API node; attempting to specify any other type of node will be rejected.
When the preceding command is invoked, all transactions running on the designated node are aborted, the connection is closed, and the server must be restarted.
The command EXIT SINGLE USER MODE changes the state of the cluster's data nodes from single user mode to normal mode. API nodes — such as MySQL Servers — waiting for a connection (that is, waiting for the cluster to become ready and available), are again permitted to connect. The API node denoted as the single-user node continues to run (if still connected) during and after the state change.
Example:
ndb_mgm> EXIT SINGLE USER MODE
There are two recommended ways to handle a node failure when running in single user mode:
Method 1:
Finish all single user mode transactions
Issue the EXIT SINGLE USER MODE command
Restart the cluster's data nodes
Method 2:
Restart database nodes prior to entering single user mode.
This section discusses several SQL statements that can prove useful in managing and monitoring a MySQL server that is connected to a MySQL Cluster, and in some cases provide information about the cluster itself.
SHOW ENGINE NDB STATUS
, SHOW
ENGINE NDBCLUSTER STATUS
The output of this statement contains information about the server's connection to the cluster, creation and usage of MySQL Cluster objects, and binary logging for MySQL Cluster replication.
See Section 12.5.4.9, “SHOW ENGINE
Syntax”, for a usage example and
more detailed information.
SHOW ENGINES [LIKE 'NDB%']
This statement can be used to determine whether or not clustering support is enabled in the MySQL server, and if so, whether it is active.
See Section 12.5.4.10, “SHOW ENGINES
Syntax”, for more detailed
information.
SHOW VARIABLES LIKE 'NDB%'
This statement provides a list of most server system variables
relating to the NDB
storage engine, and
their values, as shown here:
mysql> SHOW VARIABLES LIKE 'NDB%';
+-------------------------------------+-------+
| Variable_name | Value |
+-------------------------------------+-------+
| ndb_autoincrement_prefetch_sz | 32 |
| ndb_cache_check_time | 0 |
| ndb_extra_logging | 0 |
| ndb_force_send | ON |
| ndb_index_stat_cache_entries | 32 |
| ndb_index_stat_enable | OFF |
| ndb_index_stat_update_freq | 20 |
| ndb_report_thresh_binlog_epoch_slip | 3 |
| ndb_report_thresh_binlog_mem_usage | 10 |
| ndb_use_copying_alter_table | OFF |
| ndb_use_exact_count | ON |
| ndb_use_transactions | ON |
+-------------------------------------+-------+
See Section 5.1.3, “System Variables”, for more information.
SHOW STATUS LIKE 'NDB%'
This statement shows at a glance whether or not the MySQL server is acting as a cluster SQL node, and if so, it provides the MySQL server's cluster node ID, the hostname and port for the cluster management server to which it is connected, and the number of data nodes in the cluster, as shown here:
mysql> SHOW STATUS LIKE 'NDB%';
+--------------------------+---------------+
| Variable_name | Value |
+--------------------------+---------------+
| Ndb_cluster_node_id | 10 |
| Ndb_config_from_host | 192.168.0.103 |
| Ndb_config_from_port | 1186 |
| Ndb_number_of_data_nodes | 4 |
+--------------------------+---------------+
If the MySQL server was built with clustering support, but it is not connected to a cluster, all rows in the output of this statement contain a zero or an empty string:
mysql> SHOW STATUS LIKE 'NDB%';
+--------------------------+-------+
| Variable_name | Value |
+--------------------------+-------+
| Ndb_cluster_node_id | 0 |
| Ndb_config_from_host | |
| Ndb_config_from_port | 0 |
| Ndb_number_of_data_nodes | 0 |
+--------------------------+-------+
See also Section 12.5.4.23, “SHOW STATUS
Syntax”.
This section discusses security considerations to take into account when setting up and running MySQL Cluster.
Topics to be covered in this chapter include the following:
MySQL Cluster and network security issues
Configuration issues relating to running MySQL Cluster securely
MySQL Cluster and the MySQL privilege system
MySQL standard security procedures as applicable to MySQL Cluster
In this section, we discuss basic network security issues as they relate to MySQL Cluster. It is extremely important to remember that MySQL Cluster “out of the box” is not secure; you or your network administrator must take the proper steps to insure that your cluster cannot be compromised over the network.
Cluster communication protocols are inherently insecure, and no encryption or similar security measures are used in communications between nodes in the cluster. Because network speed and latency have a direct impact on the cluster's efficiency, it is also not advisable to employ SSL or other encryption to network connections between nodes, as such schemes will effectively slow communications.
It is also true that no authentication is used for controlling API node access to a MySQL Cluster. As with encryption, the overhead of imposing authentication requirements would have an adverse impact on Cluster performance.
In addition, there is no checking of the source IP address for either of the following when accessing the cluster:
SQL or API nodes using “free slots” created by
empty [mysqld]
or
[api]
sections in the
config.ini
file
This means that, if there are any empty
[mysqld]
or [api]
sections in the config.ini
file, then
any API nodes (including SQL nodes) that know the management
server's hostname (or IP address) and port can connect to
the cluster and access its data without restriction. (See
Section 16.8.2, “MySQL Cluster and MySQL Privileges”,
for more information about this and related issues.)
You can exercise some control over SQL and API node access
to the cluster by specifying a HostName
parameter for all [mysqld]
and
[api]
sections in the
config.ini
file. However, this also
means that, should you wish to connect an API node to the
cluster from a previously unused host, you need to add an
[api]
section containing its hostname
to the config.ini
file.
More information is available
elsewhere
in this chapter about the
HostName
parameter. Also see
Section 16.3.3, “Quick Test Setup of MySQL Cluster”, for configuration
examples using HostName
with API nodes.
Any ndb_mgm client
This means that any cluster management client that is given
the management server's hostname (or IP address) and port
(if not the standard port) can connect to the cluster and
execute any management client command. This includes
commands such as ALL STOP
and
SHUTDOWN
.
For these reasons, it is necessary to protect the cluster on the network level. The safest network configuration for Cluster is one which isolates connections between Cluster nodes from any other network communications. This can be accomplished by any of the following methods:
Keeping Cluster nodes on a network that is physically separate from any public networks. This option is the most dependable; however, it is the most expensive to implement.
We show an example of a MySQL Cluster setup using such a physically segregated network here:
This setup has two networks, one private (solid box) for the Cluster management servers and data nodes, and one public (dotted box) where the SQL nodes reside. (We show the management and data nodes connected using a gigabit switch since this provides the best performance.) Both networks are protected from the outside by a hardware firewall, sometimes also known as a network-based firewall.
This network setup is safest because no packets can reach the cluster's management or data nodes from outside the network — and none of the cluster's internal communications can reach the outside — without going through the SQL nodes, as long as the SQL nodes do not allow any packets to be forwarded. This means, of course, that all SQL nodes must be secured against hacking attempts.
With regard to potential security vulnerabilities, an SQL node is no different from any other MySQL server. See Section 5.3.2, “Making MySQL Secure Against Attackers”, for a description of techniques you can use to secure MySQL servers.
Using one or more software firewalls (also known as host-based firewalls) to control which packets pass through to the cluster from portions of the network that do not require access to it. In this type of setup, a software firewall must be installed on every host in the cluster which might otherwise be accessible from outside the local network.
The host-based option is the least expensive to implement, but relies purely on software to provide protection and so is the most difficult to keep secure.
This type of network setup for MySQL Cluster is illustrated here:
Using this type of network setup means that there are two zones of MySQL Cluster hosts. Each cluster host must be able to communicate with all of the other machines in the cluster, but only those hosting SQL nodes (dotted box) can be permitted to have any contact with the outside, while those in the zone containing the data nodes and management nodes (solid box) must be isolated from any machines that are not part of the cluster. Applications using the cluster and user of those applications must not be permitted to have direct access to the management and data node hosts.
To accomplish this, you must set up software firewalls that limit the traffic to the type or types shown in the following table, according to the type of node that is running on each cluster host computer:
Type of Node to be Accessed | Traffic to Allow |
---|---|
SQL or API node |
|
Data node or Management node |
|
Any traffic other than that shown in the table for a given node type should be denied.
The specifics of configuring a firewall vary from firewall application to firewall application. They are beyond the scope of this book, and will not be covered in the certification exam. iptables is a very common and reliable firewall application, which is often used with APF as a front end to make configuration easier. You can (and should) consult the documentation for the software firewall that you employ, should you choose to implement a MySQL Cluster network setup of this type, or of a “mixed” type as discussed under the next item.
It is also possible to employ a combination of the first two methods, using both hardware and software to secure the cluster — that is, using both network-based and host-based firewalls. This is between the first two schemes in terms of both security level and cost. This type of network setup keeps the cluster behind the hardware firewall, but allows incoming packets to travel beyond the router connecting all cluster hosts in order to reach the SQL nodes.
One possible network deployment of a MySQL Cluster using hardware and software firewalls in combination is shown here:
In this case, you can set the rules in the hardware firewall to deny any external traffic except to SQL nodes and API nodes, and then allow traffic to them only on the ports required by your application.
Whatever network configuration you use, remember that your objective from the viewpoint of keeping the cluster secure remains the same — to prevent any unessential traffic from reaching the cluster while ensuring the most efficient communication between the nodes in the cluster.
Because MySQL Cluster requires large numbers of ports to be open for communications between nodes, the recommended option is to use a segregated network. This represents the simplest way to prevent unwanted traffic from reaching the cluster.
If you wish to administer a MySQL Cluster remotely (that is, from outside the local network), the recommended way to do this is to use ssh or another secure login shell to access an SQL node host. From this host, you can then run the management client to access the management server safely, from within the Cluster's own local network.
Even though it is possible to do so in theory, it is not recommended to use ndb_mgm to manage a Cluster directly from outside the local network on which the Cluster is running. Since neither authentication nor encryption takes place between the management client and the management server, this represents an extremely insecure means of managing the cluster, and is almost certain to be compromised sooner or later.
In this section, we discuss how the MySQL privilege system works in relation to MySQL Cluster and the implications of this for keeping a MySQL Cluster secure.
Standard MySQL privileges apply to MySQL Cluster tables. This
includes all MySQL privilege types (SELECT
privilege, UPDATE
privilege,
DELETE
privilege, and so on) granted on the
database, table, and column level. As with any other MySQL Server,
user and privilege information is stored in the
mysql
system database. The SQL statements used
to grant and revoke privileges on NDB
tables,
databases containing such tables, and columns within such tables
are identical in all respects with the GRANT
and REVOKE
statements used in connection with
database objects involving any (other) MySQL storage engine. The
same thing is true with respect to the CREATE
USER
and DROP USER
statements.
It is important to keep in mind that the MySQL grant tables use
the MyISAM
storage engine. Because of this,
those tables are not duplicated or shared among MySQL servers
acting as SQL nodes in a MySQL Cluster. By way of example, suppose
that two SQL nodes A and
B are connected to the same MySQL
Cluster, which has an NDB
table named
mytable
in a database named
mydb
, and that you execute an SQL statement on
server A that creates a new user
jon@localhost
and grants this user the
SELECT
privilege on that table:
mysql>GRANT SELECT ON mydb.mytable
->TO jon@localhost IDENTIFIED BY 'mypass';
This user is not created on server B. In order for this to take place, the statement must also be run on server B. Similarly, statements run on server A and affecting the privileges of existing users on server A do not affect users on server B unless those statements are actually run on server B as well.
In other words, changes in users and their privileges do not automatically propagate between SQL nodes. Synchronization of privileges between SQL nodes must be done either manually or by scripting an application that periodically synchronizes the privilege tables on all SQL nodes in the cluster.
Conversely, because there is no way in MySQL to deny privileges
(privileges can either be revoked or not granted in the first
place, but not denied as such), there is no special protection for
NDB
tables on one SQL node from users that have
privileges on another SQL node. The most far-reaching example of
this is the MySQL root
account, which can
perform any action on any database object. In combination with
empty [mysqld]
or [api]
sections of the config.ini
file, this account
can be especially dangerous. To understand why, consider the
following scenario:
The config.ini
file contains at least
one empty [mysqld]
or
[api]
section. This means that the
Cluster management server performs no checking of the host
from which a MySQL Server (or other API node) accesses the
MySQL Cluster.
There is no firewall, or the firewall fails to protect against access to the Cluster from hosts external to the network.
The hostname or IP address of the Cluster's management server is known or can be determined from outside the network.
If these conditions are true, then anyone, anywhere can start a
MySQL Server with --ndbcluster
--ndb-connectstring=
and access the Cluster. Using the MySQL management_host
root
account, this person can then perform the following actions:
Execute a SHOW DATABASES
statement to
obtain a list of all databases that exist in the cluster
Execute a SHOW TABLES FROM
statement
to obtain a list of all some_database
NDB
tables in a
given database
Run any legal MySQL statements on any of those tables, such as:
SELECT * FROM
to
read all the data from any table
some_table
DELETE FROM
to
delete all the data from a table
some_table
DESCRIBE
or
some_table
SHOW CREATE TABLE
to
determine the table schema
some_table
UPDATE
to
fill a table column with “garbage” data;
this could actually cause much greater damage than
simply deleting all the data
some_table
SET column1
=
any_value1
Even more insidious variations might include statements like these:
UPDATEsome_table
SETan_int_column
=an_int_column
+ 1
or
UPDATEsome_table
SETa_varchar_column
= REVERSE(a_varchar_column
)
Such malicious statements are limited only by the imagination of the attacker.
The only tables that would be safe from this sort of mayhem
would be those tables that were created using storage
engines other than NDB
, and so not
visible to a “rogue” SQL node.
A user who can log in as root
can also
access the INFORMATION_SCHEMA
database
and its tables, and so obtain information about databases,
tables, stored routines, scheduled events, and any other
database objects for which metadata is stored in
INFORMATION_SCHEMA
.
It is also a very good idea to use different passwords for
the root
accounts on different cluster
SQL nodes.
In sum, you cannot have a safe MySQL Cluster if it is directly accessible from outside your local network.
Never leave the MySQL root account password empty. This is just as true when running MySQL as a MySQL Cluster SQL node as it is when running it as a standalone (non-Cluster) MySQL Server, and should be done as part of the MySQL installation process before configuring the MySQL Server as an SQL node in a MySQL Cluster.
You should never convert the system tables in the
mysql
database to use the
NDB
storage engine. There are a number of
reasons why you should not do this, but the most important reason
is this: Many of the SQL statements that affect
mysql
tables storing information about user
privileges, stored routines, scheduled events, and other database
objects cease to function if these tables are changed to use any
storage engine other than MyISAM
.
This is a consequence of various MySQL Server internals which are
not expected to change in the foreseeable future.
If you need to synchronize mysql
system tables
between SQL nodes, you can use standard MySQL replication to do
so, or employ a script to copy table entries between the MySQL
servers.
Summary. The two most important points to remember regarding the MySQL privilege system with regard to MySQL Cluster are:
Users and privileges established on one SQL node do not automatically exist or take effect on other SQL nodes in the cluster.
Conversely, removing a user or privilege on one SQL node in the cluster does not remove the user or privilege from any other SQL nodes.
Once a MySQL user is granted privileges on an
NDB
table from one SQL node in a MySQL
Cluster, that user can “see” any data in that
table regardless of the SQL node from which the data
originated.
In this section, we discuss MySQL standard security procedures as they apply to running MySQL Cluster.
In general, any standard procedure for running MySQL securely also
applies to running a MySQL Server as part of a MySQL Cluster.
First and foremost, you should always run a MySQL Server as the
mysql
system user; this is no different from
running MySQL in a standard (non-Cluster) environment. The
mysql
system account should be uniquely and
clearly defined. Fortunately, this is the default behavior for a
new MySQL installation. You can verify that the
mysqld process is running as the system user
mysql
by using the system command such as the
one shown here:
shell> ps aux | grep mysql
root 10467 0.0 0.1 3616 1380 pts/3 S 11:53 0:00 \
/bin/sh ./mysqld_safe --ndbcluster --ndb-connectstring=localhost:1186
mysql 10512 0.2 2.5 58528 26636 pts/3 Sl 11:53 0:00 \
/usr/local/mysql/libexec/mysqld --basedir=/usr/local/mysql \
--datadir=/usr/local/mysql/var --user=mysql --ndbcluster \
--ndb-connectstring=localhost:1186 --pid-file=/usr/local/mysql/var/mothra.pid \
--log-error=/usr/local/mysql/var/mothra.err
jon 10579 0.0 0.0 2736 688 pts/0 S+ 11:54 0:00 grep mysql
If the mysqld process is running as any other
user than mysql
, you should immediately shut it
down and restart it as the mysql
user. If this
user does not exist on the system, the mysql
user account should be created, and this user should be part of
the mysql
user group; in this case, you should
also make sure that the MySQL DataDir
on this
system is owned by the mysql
user, and that the
SQL node's my.cnf
file includes
user=mysql
in the [mysqld]
section. Alternatively, you can start the server with
--user=mysql
on the command line, but it is
preferable to use the my.cnf
option, since
you might forget to use the command line option and so have
mysqld running as another user unintentionally.
The mysqld_safe startup script forces MySQL to
run as the mysql
user.
Never run mysqld as the system root user. Doing so means that potentially any file on the system can be read by MySQL, and thus — should MySQL be compromised — by an attacker.
As mentioned in the previous section (see Section 16.8.2, “MySQL Cluster and MySQL Privileges”), you should always set a root password for the MySQL Server as soon as you have it running. You should also delete the anonymous user account that is installed by default. You can accomplish these tasks via the following statements:
shell<mysql -u root
mysql>UPDATE mysql.user
->SET Password=PASSWORD('
->secure_password
')WHERE User='root';
mysql>DELETE FROM mysql.user
->WHERE User='';
mysql>FLUSH PRIVILEGES;
Be very careful when executing the DELETE
statement not to omit the WHERE
clause, or you
risk deleting all MySQL users. Be sure to run
the FLUSH PRIVILEGES
statement as soon as you
have modified the mysql.user
table, so that the
changes take immediate effect. Without FLUSH
PRIVILEGES
, the changes do not take effect until the
next time that the server is restarted.
Many of the MySQL Cluster utilities such as
ndb_show_tables, ndb_desc,
and ndb_select_all also work without
authentication and can reveal table names, schemas, and data. By
default these are installed on Unix-style systems with the
permissions wxr-xr-x
(755), which means they
can be executed by any user that can access the
mysql/bin
directory.
See Section 16.10, “Cluster Utility Programs”, for more information about these utilities.
This section describes how to create a backup and how to restore the database from a backup at a later time.
A backup is a snapshot of the database at a given time. The backup consists of three main parts:
Metadata. The names and definitions of all database tables
Table records. The data actually stored in the database tables at the time that the backup was made
Transaction log. A sequential record telling how and when data was stored in the database
Each of these parts is saved on all nodes participating in the backup. During backup, each node saves these three parts into three files on disk:
BACKUP-
backup_id
.node_id
.ctl
A control file containing control information and metadata. Each node saves the same table definitions (for all tables in the cluster) to its own version of this file.
BACKUP-
backup_id
-0.node_id
.data
A data file containing the table records, which are saved on a per-fragment basis. That is, different nodes save different fragments during the backup. The file saved by each node starts with a header that states the tables to which the records belong. Following the list of records there is a footer containing a checksum for all records.
BACKUP-
backup_id
.node_id
.log
A log file containing records of committed transactions. Only transactions on tables stored in the backup are stored in the log. Nodes involved in the backup save different records because different nodes host different database fragments.
In the listing above, backup_id
stands
for the backup identifier and node_id
is the unique identifier for the node creating the file.
Before starting a backup, make sure that the cluster is properly configured for performing one. (See Section 16.9.4, “Configuration for Cluster Backup”.)
Creating a backup using the management client involves the following steps:
Start the management client (ndb_mgm), if it not running already.
Execute the START BACKUP
command.
This produces several lines of output indicating the
progress of the backup, as shown here:
ndb_mgm> START BACKUP
Waiting for completed, this may take several minutes
Node 2: Backup 1 started from node 1
Node 2: Backup 1 started from node 1 completed
StartGCP: 177 StopGCP: 180
#Records: 7362 #LogRecords: 0
Data: 453648 bytes Log: 0 bytes
ndb_mgm>
The first line printed indicates that the management client
is waiting for the backup to be completed before returning
control to the client. This behavior is the default for the
START BACKUP
command, but can be changed.
To specify when START BACKUP
command
should return control to the client, append
NOWAIT
, WAIT STARTED
,
or WAIT COMPLETED
to the command. The
effects that each of these has differs as follows:
If NOWAIT
is specified, the
management client displays a prompt immediately, as
seen here:
ndb_mgm> START BACKUP NOWAIT
ndb_mgm>
In this case, the management client can be used even while it prints progress information from the backup process.
With WAIT STARTED
the management
client waits until the backup has started before
returning control to the user, as shown here:
ndb_mgm> START BACKUP WAIT STARTED
Waiting for started, this may take several minutes
Node 2: Backup 3 started from node 1
ndb_mgm>
WAIT COMPLETED
explicitly
specifies the default behavior — that is, it
causes the management client to wait until the backup
process is complete before returning control to the
user.
When the backup has started the management client displays this message:
Backupbackup_id
started from nodenode_id
backup_id
is the unique
identifier for this particular backup. This identifier is
saved in the cluster log, if it has not been configured
otherwise. node_id
is the
identifier of the management server that is coordinating the
backup with the data nodes. At this point in the backup
process the cluster has received and processed the backup
request. It does not mean that the backup has finished. An
example of this statement is shown here:
Node 2: Backup 1 started from node 1
The management client indicates that the backup has completed with a message in the following format:
Backupbackup_id
started from nodenode_id
completed
As is the case for the notification that the backup has
started, backup_id
is the unique
identifier for this particular backup, and
node_id
is the node ID of the
management server that is coordinating the backup with the
data nodes. This output is accompanied by additional
information including relevant global checkpoints, the
number of records backed up, and the size of the data, as
shown here:
Node 2: Backup 1 started from node 1 completed StartGCP: 177 StopGCP: 180 #Records: 7362 #LogRecords: 0 Data: 453648 bytes Log: 0 bytes
Cluster backups are created by default in the
BACKUP
subdirectory of the
DataDir
on each data node. This can be
overridden for one or more data nodes individually, or for all
cluster data nodes in the config.ini
file
using the BackupDataDir
configuration parameter
as discussed in
Identifying
Data Nodes. The backup files created for a backup with a
given backup_id
are stored in a
subdirectory named
BACKUP-
in the backup directory.
backup_id
To abort a backup that is already in progress:
Start the management client.
Execute this command:
ndb_mgm> ABORT BACKUP backup_id
The number backup_id
is the
identifier of the backup that was included in the response of
the management client when the backup was started (in the
message Backup
).
backup_id
started from node
management_node_id
The management client will acknowledge the abort request with
Abort of backup
.
backup_id
ordered
At this point, the management client has not yet received a response from the cluster data nodes to this request, and the backup has not yet actually been aborted.
After the backup has been aborted, the management client will report this fact in a manner similar to what is shown here:
Node 1: Backup 3 started from 5 has been aborted. Error: 1321 - Backup aborted by user request: Permanent error: User defined error Node 3: Backup 3 started from 5 has been aborted. Error: 1323 - 1323: Permanent error: Internal error Node 2: Backup 3 started from 5 has been aborted. Error: 1323 - 1323: Permanent error: Internal error Node 4: Backup 3 started from 5 has been aborted. Error: 1323 - 1323: Permanent error: Internal error
In this example, we have shown sample output for a cluster
with 4 data nodes, where the sequence number of the backup to
be aborted is 3
, and the management node to
which the cluster management client is connected has the node
ID 5
. The first node to complete its part
in aborting the backup reports that the reason for the abort
was due to a request by the user. (The remaining nodes report
that the backup was aborted due to an unspecified internal
error.)
There is no guarantee that the cluster nodes respond to an
ABORT BACKUP
command in any particular
order.
The Backup
messages mean that the backup has been
terminated and that all files relating to this backup have
been removed from the cluster filesystem.
backup_id
started from node
management_node_id
has been
aborted
It is also possible to abort a backup in progress from a system shell using this command:
shell> ndb_mgm -e "ABORT BACKUP backup_id
"
If there is no backup with ID
backup_id
running when an
ABORT BACKUP
is issued, the management client
makes no response, nor is it indicated in the cluster log that
an invalid abort command was sent.
The cluster restoration program is implemented as a separate
command-line utility ndb_restore, which can
normally be found in the MySQL bin
directory. This program reads the files created as a result of
the backup and inserts the stored information into the
database.
ndb_restore must be executed once for each
of the backup files that were created by the START
BACKUP
command used to create the backup (see
Section 16.9.2, “Using The Management Client to Create a Backup”).
This is equal to the number of data nodes in the cluster at
the time that the backup was created.
Before using ndb_restore, it is recommended that the cluster be running in single user mode, unless you are restoring multiple data nodes in parallel. See Section 16.7.4, “Single User Mode”, for more information about single user mode.
Typical options for this utility are shown here:
ndb_restore [-cconnectstring
] -nnode_id
[-m] -bbackup_id
-r [backup_path=]/path/to/backup/files
The -c
option is used to specify a
connectstring which tells ndb_restore
where
to locate the cluster management server. (See
Section 16.3.4.2, “The Cluster Connectstring”, for information
on connectstrings.) If this option is not used, then
ndb_restore attempts to connect to a
management server on localhost:1186
. This
utility acts as a cluster API node, and so requires a free
connection “slot” to connect to the cluster
management server. This means that there must be at least one
[api]
or [mysqld]
section that can be used by it in the cluster
config.ini
file. It is a good idea to
keep at least one empty [api]
or
[mysqld]
section in
config.ini
that is not being used for a
MySQL server or other application for this reason (see
Section 16.3.4.6, “Defining SQL and Other API Nodes”).
You can verify that ndb_restore is connected to the cluster by using the SHOW command in the ndb_mgm management client. You can also accomplish this from a system shell, as shown here:
shell> ndb_mgm -e "SHOW"
-n
is used to specify the node ID of the data
node on which the backups were taken.
The first time you run the ndb_restore
restoration program, you also need to restore the metadata. In
other words, you must re-create the database tables —
this can be done by running it with the -m
option. Note that the cluster should have an empty database
when starting to restore a backup. (In other words, you should
start ndbd with --initial
prior to performing the restore.)
The -b
option is used to specify the ID or
sequence number of the backup, and is the same number shown by
the management client in the Backup
message displayed upon completion of a backup. (See
Section 16.9.2, “Using The Management Client to Create a Backup”.)
backup_id
completed
The path to the backup directory is required, and must include
the subdirectory corresponding to the ID backup of the backup
to be restored. For example, if the data node's
DataDir
is
/var/lib/mysql-cluster
, then the backup
directory is
/var/lib/mysql-cluster/BACKUP
, and the
backup files for the backup with the ID 3 can be found in
/var/lib/mysql-cluster/BACKUP/BACKUP-3
.
The path may be absolute or relative to the directory in which
the ndb_restore executable is located, and
may be optionally prefixed with backup_path=
.
When restoring cluster backups, you must be sure to restore all data nodes from backups having the same backup ID. Using files from different backups will at best result in restoring the cluster to an inconsistent state, and may fail altogether.
It is not possible to restore a backup made from a newer version of MySQL Cluster using an older version of ndb_restore. You can restore a backup made from a newer version of MySQL to an older cluster, but you must use a copy of ndb_restore from the newer MySQL Cluster version to do so.
For example, to restore a cluster backup taken from a cluster running MySQL 5.0.45 to a cluster running MySQL Cluster 5.0.41, you must use a copy of ndb_restore from the 5.0.45 distribution.
It is possible to restore a backup to a database with a
different configuration than it was created from. For example,
suppose that a backup with backup ID 12
,
created in a cluster with two database nodes having the node
IDs 2
and 3
, is to be
restored to a cluster with four nodes. Then
ndb_restore must be run twice — once
for each database node in the cluster where the backup was
taken. However, ndb_restore cannot always
restore backups made from a cluster running one version of
MySQL to a cluster running a different MySQL version. See
Section 16.5.2, “Cluster Upgrade and Downgrade Compatibility”,
for more information.
For more rapid restoration, the data may be restored in
parallel, provided that there is a sufficient number of
cluster connections available. That is, when restoring to
multiple nodes in parallel, you must have an
[api]
or [mysqld]
section in the cluster config.ini
file
available for each concurrent ndb_restore
process. However, the data files must always be applied
before the logs.
Most of the options available for this program are shown in the following table:
Long Form | Short Form | Description | Default Value |
--backup-id | -b | Backup sequence ID | 0 |
--backup_path | None | Path to backup files | ./ |
--character-sets-dir | None | Specify the directory where character set information can be found | None |
--connect , --connectstring , or
--ndb-connectstring | -c or -C | Set the connectstring in
[nodeid=
format | localhost:1186 |
--core-file | None | Write a core file in the event of an error | TRUE |
--debug | -# | Output debug log | d:t:O, |
--help or --usage | -? | Display help message with available options and current values, then exit | [N/A] |
--ndb-mgmd-host | None | Set the host and port in
format for the management server to connect to; this
is the same as --connect ,
--connectstring , or
--ndb-connectstring , but without a
way to specify the nodeid | None |
--ndb-nodeid | None | Specify a node ID for the ndb_restore process | 0 |
--ndb-optimized-node-selection | None | Optimize selection of nodes for transactions | TRUE |
--ndb-shm | None | Use shared memory connections when available | FALSE |
--nodeid | -n | Use backup files from node with the specified ID | 0 |
--parallelism | -p | Set from 1 to 1024 parallel transactions to be used during the restoration process | 128 |
--print | None | Print metadata, data, and log to stdout | FALSE |
--print_data | None | Print data to stdout | FALSE |
--print_log | None | Print log to stdout | FALSE |
--print_meta | None | Print metadata to stdout | FALSE |
--restore_data | -r | Restore data and logs | FALSE |
--restore_meta | -m | Restore table metadata | FALSE |
--version | -V | Output version information and exit | [N/A] |
Beginning with MySQL 5.0.40, several additional options are
available for use with the --print_data
option in generating data dumps, either to
stdout
, or to a file. These are similar to
some of the options used with mysqldump,
and are shown in the following table:
Long Form | Short Form | Description | Default Value |
--tab | -T | Creates dumpfiles, one per table, each named
.
Takes as its argument the path to the directory
where the files should be saved (required; use
. for the current directory). | None |
--fields-enclosed-by | None | String used to enclose all column values | None |
--fields-optionally-enclosed-by | None | String used to enclose column values containing character data (such as
CHAR , VARCHAR ,
BINARY , TEXT ,
or ENUM ) | None |
--fields-terminated-by | None | String used to separate column values | \t (tab character) |
--hex | None | Use hex format for binary values | [N/A] |
--lines-terminated-by | None | String used to terminate each line | \n (linefeed character) |
--append | None | When used with --tab , causes the data to be appended to
existing files of the same name | [N/A] |
If a table has no explicit primary key, then the output
generated when using the --print
includes
the table's hidden primary key.
Beginning with MySQL 5.0.40, it is possible to restore selected databases, or to restore selected tables from a given database using the syntax shown here:
ndb_restoreother_options
db_name_1
[db_name_2
[,db_name_3
][, ...] |tbl_name_1
[,tbl_name_2
][, ...]]
In other words, you can specify either of the following to be restored:
All tables from one or more databases
One or more tables from a single database
ndb_restore reports both temporary and
permanent errors. In the case of temporary errors, it may
able to recover from them. Beginning with MySQL 5.0.29, it
reports Restore successful, but encountered
temporary error, please look at configuration
in
such cases.
Five configuration parameters are essential for backup:
BackupDataBufferSize
The amount of memory used to buffer data before it is written to disk.
BackupLogBufferSize
The amount of memory used to buffer log records before these are written to disk.
BackupMemory
The total memory allocated in a database node for backups. This should be the sum of the memory allocated for the backup data buffer and the backup log buffer.
BackupWriteSize
The default size of blocks written to disk. This applies for both the backup data buffer and the backup log buffer.
BackupMaxWriteSize
The maximum size of blocks written to disk. This applies for both the backup data buffer and the backup log buffer.
More detailed information about these parameters can be found in Backup Parameters.
If an error code is returned when issuing a backup request, the most likely cause is insufficient memory or disk space. You should check that there is enough memory allocated for the backup.
If you have set BackupDataBufferSize
and
BackupLogBufferSize
and their sum is greater
than 4MB, then you must also set BackupMemory
as well. See
BackupMemory
.
You should also make sure that there is sufficient space on the hard drive partition of the backup target.
NDB
does not support repeatable reads, which
can cause problems with the restoration process. Although the
backup process is “hot”, restoring a MySQL Cluster
from backup is not a 100% “hot” process. This is due
to the fact that, for the duration of the restore process, running
transactions get non-repeatable reads from the restored data. This
means that the state of the data is inconsistent while the restore
is in progress.
MySQL Enterprise MySQL Enterprise subscribers will find more information about Cluster backup in the Knowledge Base article, How Do I Backup my Cluster Database. Access to the MySQL Knowledge Base collection of articles is one of the advantages of subscribing to MySQL Enterprise. For more information see http://www.mysql.com/products/enterprise/advisors.html.
This section discusses the MySQL Cluster utility programs that can
be found in the mysql/bin
directory. Each of
these — except for ndb_size.pl
and
ndb_error_reporter — is a standalone binary
that can be used from a system shell, and that does not need to
connect to a MySQL server (nor even requires that a MySQL server be
connected to the cluster).
These utilities can also serve as examples for writing your own
applications using the NDB
API. The source code
for most of these programs may be found in the
ndb/tools
directory of the MySQL
5.0 tree (see Section 2.4.15, “MySQL Installation Using a Source Distribution”). The
NDB
API is not covered in this manual; please
refer to the NDB
API
Guide for information about this API.
All of the NDB
utilities are listed here with
brief descriptions:
ndb_config: Retrieves Cluster configuration option values.
ndb_cpcd: Used in testing and debugging MySQL Cluster.
ndb_delete_all: Deletes all rows from a given table.
ndb_desc: Lists all properties of an
NDB
table.
ndb_drop_index: Drops the specified index
from an NDB
table.
ndb_drop_table: Drops an
NDB
table.
ndb_error_reporter: Can be used to gather information useful for diagnosing problems with the cluster.
ndb_mgm: This is the MySQL Cluster management client, which is discussed in Section 16.7.2, “Commands in the MySQL Cluster Management Client”.
ndb_print_backup_file: Prints diagnostic information obtained from cluster backup files.
ndb_print_schema_file: Prints diagnostic information obtained from cluster schema files.
ndb_print_sys_file: Prints diagnostic information obtained from cluster system files.
ndb_restore: This utility is used to restore a cluster from backup. See Section 16.9.3, “ndb_restore — Restore a Cluster Backup”, for more information.
ndb_select_all: Prints all rows from an
NDB
table.
ndb_select_count: Gets the number of rows in
one or more NDB
tables.
ndb_show_tables: Shows all
NDB
tables anywhere in the cluster.
ndb_size.pl: Examines all the tables in a
given non-Cluster database and calculates the amount of storage
each would require if it were converted to use the
NDB
storage engine.
ndb_waiter: Reports on the status of cluster
data nodes in a manner similar to that of the management client
command ALL STATUS
.
Most of these utilities need to connect to a Cluster management
server in order to function. The exceptions are
ndb_size.pl
(see below), and the following
utilities which access a cluster data node filesystem and so need to
be run on a data node host:
ndb_print_backup_file
ndb_print_schema_file
ndb_print_sys_file
ndb_size.pl
is a Perl script which is also
intended to be used from the shell; however it is a MySQL
application and must be able to connect to a MySQL server. See
Section 16.10.14, “ndb_size.pl — NDBCluster Size Requirement Estimator”, for additional
requirements for using this script.
ndb_error_reporter is also a Perl script. It is used to gather cluster data node and management node logs together into a tarball to submit along with a bug report. It can use ssh or scp to access the node filesystems remotely.
Additional information about each of these utilities (except for ndb_mgm and ndb_restore) can be found in the sections that follow.
All of these utilities (except for ndb_size.pl and ndb_config) can use the options discussed in Section 16.6.5, “Command Options for MySQL Cluster Processes”. Additional options specific to each utility program are discussed in the individual program listings.
The order in which these options are used is generally not important. For example, all of these commands produce exactly the same output:
ndb_desc -c localhost fish -d test
ndb_desc fish -c localhost -d test
ndb_desc -d test fish -c localhost
This tool extracts configuration information for data nodes,
SQL nodes, and API nodes from a cluster management node (and
possibly its config.ini
file).
Usage:
ndb_config options
The options
available for this
utility differ somewhat from those used with the other
utilities, and so are listed in their entirety in the next
section, followed by some examples.
Options:
Causes ndb_config to print a list of available options, and then exit.
Causes ndb_config to print a version information string, and then exit.
--ndb-connectstring=
connect_string
Specifies the connectstring to use in connecting to the
management server. The format for the connectstring is the
same as described in
Section 16.3.4.2, “The Cluster Connectstring”, and
defaults to localhost:1186
.
The use of -c
as a short version for
this option is supported for
ndb_config beginning with MySQL
5.0.29.
Gives the path to the management server's configuration
file (config.ini
). This may be a
relative or absolute path. If the management node resides
on a different host from the one on which
ndb_config is invoked, then an absolute
path must be used.
--query=
,
query-options
-q
query-options
This is a comma-delimited list of query
options — that is, a list of one or more
node attributes to be returned. These include
id
(node ID), type (node type —
that is, ndbd
,
mysqld
, or
ndb_mgmd
), and any configuration
parameters whose values are to be obtained.
For example,
--query=id,type,indexmemory,datamemory
would return the node ID, node type,
DataMemory
, and
IndexMemory
for each node.
If a given parameter is not applicable to a certain type of node, than an empty string is returned for the corresponding value. See the examples later in this section for more information.
Specifies the hostname of the node for which configuration information is to be obtained.
--id=
,
node_id
--nodeid=
node_id
Used to specify the node ID of the node for which configuration information is to be obtained.
(Tells ndb_config to print information
from parameters defined in [ndbd]
sections only. Currently, using this option has no affect,
since these are the only values checked, but it may become
possible in future to query parameters set in
[tcp]
and other sections of cluster
configuration files.)
Filters results so that only configuration values applying
to nodes of the specified
node_type
(ndbd
, mysqld
, or
ndb_mgmd
) are returned.
--fields=
,
delimiter
-f
delimiter
Specifies a delimiter
string
used to separate the fields in the result. The default is
“,
” (the comma character).
If the delimiter
contains
spaces or escapes (such as \n
for the
linefeed character), then it must be quoted.
--rows=
,
separator
-r
separator
Specifies a separator
string
used to separate the rows in the result. The default is a
space character.
If the separator
contains
spaces or escapes (such as \n
for the
linefeed character), then it must be quoted.
Examples:
To obtain the node ID and type of each node in the cluster:
shell> ./ndb_config --query=id,type --fields=':' --rows='\n'
1:ndbd
2:ndbd
3:ndbd
4:ndbd
5:ndb_mgmd
6:mysqld
7:mysqld
8:mysqld
9:mysqld
In this example, we used the --fields
options to separate the ID and type of each node with a
colon character (:
), and the
--rows
options to place the values for
each node on a new line in the output.
To produce a connectstring that can be used by data, SQL, and API nodes to connect to the management server:
shell> ./ndb_config --config-file=usr/local/mysql/cluster-data/config.ini --query=hostname,portnumber --fields=: --rows=, --type=ndb_mgmd
192.168.0.179:1186
This invocation of ndb_config checks
only data nodes (using the --type
option), and shows the values for each node's ID and
hostname, and its DataMemory
,
IndexMemory
, and
DataDir
parameters:
shell> ./ndb_config --type=ndbd --query=id,host,datamemory,indexmemory,datadir -f ' : ' -r '\n'
1 : 192.168.0.193 : 83886080 : 18874368 : /usr/local/mysql/cluster-data
2 : 192.168.0.112 : 83886080 : 18874368 : /usr/local/mysql/cluster-data
3 : 192.168.0.176 : 83886080 : 18874368 : /usr/local/mysql/cluster-data
4 : 192.168.0.119 : 83886080 : 18874368 : /usr/local/mysql/cluster-data
In this example, we used the short options
-f
and -r
for setting
the field delimiter and row separator, respectively.
To exclude results from any host except one in particular,
use the --host
option:
shell> ./ndb_config --host=192.168.0.176 -f : -r '\n' -q id,type
3:ndbd
5:ndb_mgmd
In this example, we also used the short form
-q
to determine the attributes to be
queried.
Similarly, you can limit results to a node with a specific
ID using the --id
or
--nodeid
option.
This utility is found in the libexec
directory. It is part of an internal automated test framework
used in testing and bedugging MySQL Cluster. Because it can
control processes on remote systems, it is not advisable to
use ndb_cpcd in a production cluster.
Because some users may be interested in employing the Cluster testing framework for their own development or testing purposes, we intend to make details of this application's usage available in the near future as part of the MySQL Internals Manual.
The source files for ndb_cpcd may be found
in the directory storage/ndb/src/cw/cpcd
,
in the MySQL 5.0 source tree.
ndb_delete_all deletes all rows from the
given NDB
table. In some cases, this can be
much faster than DELETE
or even
TRUNCATE
.
Usage:
ndb_delete_all -cconnect_string
tbl_name
-ddb_name
This deletes all rows from the table named
tbl_name
in the database named
db_name
. It is exactly equivalent
to executing TRUNCATE
in MySQL.
db_name
.tbl_name
Additional Options:
ndb_desc provides a detailed description of
one or more NDB
tables.
Usage:
ndb_desc -cconnect_string
tbl_name
-ddb_name
Sample Output:
MySQL table creation and population statements:
USE test; CREATE TABLE fish ( id INT(11) NOT NULL AUTO_INCREMENT, name VARCHAR(20), PRIMARY KEY pk (id), UNIQUE KEY uk (name) ) ENGINE=NDBCLUSTER; INSERT INTO fish VALUES ('','guppy'), ('','tuna'), ('','shark'), ('','manta ray'), ('','grouper'), ('','puffer');
Output from ndb_desc:
shell> ./ndb_desc -c localhost fish -d test -p
-- fish --
Version: 16777221
Fragment type: 5
K Value: 6
Min load factor: 78
Max load factor: 80
Temporary table: no
Number of attributes: 2
Number of primary keys: 1
Length of frm data: 268
Row Checksum: 1
Row GCI: 1
TableStatus: Retrieved
-- Attributes --
id Int PRIMARY KEY DISTRIBUTION KEY AT=FIXED ST=MEMORY
name Varchar(20;latin1_swedish_ci) NULL AT=SHORT_VAR ST=MEMORY
-- Indexes --
PRIMARY KEY(id) - UniqueHashIndex
uk(name) - OrderedIndex
PRIMARY(id) - OrderedIndex
uk$unique(name) - UniqueHashIndex
-- Per partition info --
Partition Row count Commit count Frag fixed memory Frag varsized memory
2 2 2 65536 327680
1 2 2 65536 327680
3 2 2 65536 327680
NDBT_ProgramExit: 0 - OK
Additional Options:
ndb_drop_index drops the specified index
from an NDB
table. It is
recommended that you use this utility only as an example for
writing NDB API applications — see the
Warning later in this section for details.
Usage:
ndb_drop_index -cconnect_string
table_name
index
-ddb_name
The statement shown above drops the index named
index
from the
table
in the
database
.
Additional Options: None that are specific to this application.
Operations performed on Cluster table indexes using the NDB API are not visible to MySQL and make the table unusable by a MySQL server. If you use this program to drop an index, then try to access the table from an SQL node, an error results, as shown here:
shell>./ndb_drop_index -c localhost dogs ix -d ctest1
Dropping index dogs/idx...OK NDBT_ProgramExit: 0 - OK shell>./mysql -u jon -p ctest1
Enter password: ******* Reading table information for completion of table and column names You can turn off this feature to get a quicker startup with -A Welcome to the MySQL monitor. Commands end with ; or \g. Your MySQL connection id is 7 to server version: 5.1.12-beta-20060817 Type 'help;' or '\h' for help. Type '\c' to clear the buffer. mysql> SHOW TABLES; +------------------+ | Tables_in_ctest1 | +------------------+ | a | | bt1 | | bt2 | | dogs | | employees | | fish | +------------------+ 6 rows in set (0.00 sec) mysql> SELECT * FROM dogs; ERROR 1296 (HY000): Got error 4243 'Index not found' from NDBCLUSTER
In such a case, your only option for
making the table available to MySQL again is to drop the table
and re-create it. You can use either the SQL
statementDROP TABLE
or the
ndb_drop_table utility (see
Section 16.10.6, “ndb_drop_table — Drop NDB Table”) to
drop the table.
ndb_drop_table drops the specified
NDB
table. (If you try to use this on a
table created with a storage engine other than NDB, it fails
with the error 723: No such table
exists.) This operation is extremely fast —
in some cases, it can be an order of magnitude faster than
using DROP TABLE
on an
NDB
table from MySQL.
Usage:
ndb_drop_table -cconnect_string
tbl_name
-ddb_name
Additional Options: None.
ndb_error_reporter creates an archive from data node and management node log files that can be used to help diagnose bugs or other problems with a cluster. It is highly recommended that you make use of this utility when filing reports of bugs in MySQL Cluster.
Usage:
ndb_error_reporterpath/to/config-file
[username
] [--fs]
This utility is intended for use on a management node host,
and requires the path to the management host configuration
file (config.ini
). Optionally, you can
supply the name of a user that is able to access the cluster's
data nodes via SSH, in order to copy the data node log files.
ndb_error_reporter then includes all of these files in archive
that is created in the same directory in which it is run. The
archive is named
ndb_error_report_
,
where YYYYMMDDHHMMSS
.tar.bz2YYYYMMDDHHMMSS
is a datetime
string.
If the --fs
is used, then the data node
filesystems are also copied to the management host and
included in the archive that is produced by this script. As
data node filesystems can be extremely large even after being
compressed, we ask that you please do not
send archives created using this option to MySQL AB unless you
are specifically requested to do so.
ndb_print_backup_file obtains diagnostic information from a cluster backup file.
Usage:
ndb_print_backup_file file_name
file_name
is the name of a cluster
backup file. This can be any of the files
(.Data
, .ctl
, or
.log
file) found in a cluster backup
directory. These files are found in the data node's backup
directory under the subdirectory
BACKUP-
,
where #
#
is the sequence number for
the backup. For more information about cluster backup files
and their contents, see
Section 16.9.1, “Cluster Backup Concepts”.
Like ndb_print_schema_file and
ndb_print_sys_file (and unlike most of the
other NDB
utilities that are intended to be
run on a management server host or to connect to a management
server) ndb_print_backup_file must be run
on a cluster data node, since it accesses the data node
filesystem directly. Because it does not make use of the
management server, this utility can be used when the
management server is not running, and even when the cluster
has been completely shut down.
Additional Options: None.
ndb_print_schema_file obtains diagnostic information from a cluster schema file.
Usage:
ndb_print_schema_file file_name
file_name
is the name of a cluster
schema file.
Like ndb_print_backup_file and
ndb_print_sys_file (and unlike most of the
other NDB
utilities that are intended to be
run on a management server host or to connect to a management
server) ndb_schema_backup_file must be run
on a cluster data node, since it accesses the data node
filesystem directly. Because it does not make use of the
management server, this utility can be used when the
management server is not running, and even when the cluster
has been completely shut down.
Additional Options: None.
ndb_print_sys_file obtains diagnostic information from a cluster system file.
Usage:
ndb_print_sys_file file_name
file_name
is the name of a cluster
system file (sysfile). Cluster system files are located in a
data node's data directory (DataDir
); the
path under this directory to system files matches the pattern
ndb_
.
In each case, the #
_fs/D#
/DBDIH/P#
.sysfile#
represents a
number (not necessarily the same number).
Like ndb_print_backup_file and
ndb_print_schema_file (and unlike most of
the other NDB
utilities that are intended
to be run on a management server host or to connect to a
management server) ndb_print_backup_file
must be run on a cluster data node, since it accesses the data
node filesystem directly. Because it does not make use of the
management server, this utility can be used when the
management server is not running, and even when the cluster
has been completely shut down.
Additional Options: None.
ndb_select_all prints all rows from an
NDB
table to stdout
.
Usage:
ndb_select_all -cconnect_string
tbl_name
-ddb_name
[>file_name
]
Additional Options:
--lock=
,
lock_type
-l
lock_type
Employs a lock when reading the table. Possible values for
lock_type
are:
0
: Read lock
1
: Read lock with hold
2
: Exclusive read lock
There is no default value for this option.
--order=
,
index_name
-o
index_name
Orders the output according to the index named
index_name
. Note that this is
the name of an index, not of a column, and that the index
must have been explicitly named when created.
Sorts the output in descending order. This option can be
used only in conjunction with the -o
(--order
) option.
Excludes column headers from the output.
Causes all numeric values to be displayed in hexadecimal format. This does not affect the output of numerals contained in strings or datetime values.
--delimiter=
,
character
-D
character
Causes the character
to be used
as a column delimiter. Only table data columns are
separated by this delimiter.
The default delimiter is the tab character.
Adds a ROWID
column providing
information about the fragments in which rows are stored.
Adds a column to the output showing the global checkpoint at which each row was last updated. See Section 16.14, “MySQL Cluster Glossary”, and Section 16.7.3.2, “Log Events”, for more information about checkpoints.
Scan the table in the order of the tuples.
Causes any table data to be omitted.
Sample Output:
Output from a MySQL SELECT
statement:
mysql> SELECT * FROM ctest1.fish;
+----+-----------+
| id | name |
+----+-----------+
| 3 | shark |
| 6 | puffer |
| 2 | tuna |
| 4 | manta ray |
| 5 | grouper |
| 1 | guppy |
+----+-----------+
6 rows in set (0.04 sec)
Output from the equivalent invocation of ndb_select_all:
shell> ./ndb_select_all -c localhost fish -d ctest1
id name
3 [shark]
6 [puffer]
2 [tuna]
4 [manta ray]
5 [grouper]
1 [guppy]
6 rows returned
NDBT_ProgramExit: 0 - OK
Note that all string values are enclosed by square brackets
(“[
...]
”)
in the output of ndb_select_all. For a
further example, consider the table created and populated as
shown here:
CREATE TABLE dogs ( id INT(11) NOT NULL AUTO_INCREMENT, name VARCHAR(25) NOT NULL, breed VARCHAR(50) NOT NULL, PRIMARY KEY pk (id), KEY ix (name) ) ENGINE=NDB; INSERT INTO dogs VALUES ('', 'Lassie', 'collie'), ('', 'Scooby-Doo', 'Great Dane'), ('', 'Rin-Tin-Tin', 'German Shepherd'), ('', 'Rosscoe', 'Mutt');
This demonstrates the use of several additional ndb_select_all options:
shell> ./ndb_select_all -d ctest1 dogs -o ix -z --gci
GCI id name breed
834461 2 [Scooby-Doo] [Great Dane]
834878 4 [Rosscoe] [Mutt]
834463 3 [Rin-Tin-Tin] [German Shepherd]
835657 1 [Lassie] [Collie]
4 rows returned
NDBT_ProgramExit: 0 - OK
ndb_select_count prints the number of rows
in one or more NDB
tables. With a single
table, the result is equivalent to that obtained by using the
MySQL statement SELECT COUNT(*) FROM
.
tbl_name
Usage:
ndb_select_count [-cconnect_string
] -ddb_name
tbl_name
[,tbl_name2
[, ...]]
Additional Options: None that are specific to this application. However, you can obtain row counts from multiple tables in the same database by listing the table names separated by spaces when invoking this command, as shown under Sample Output.
Sample Output:
shell> ./ndb_select_count -c localhost -d ctest1 fish dogs
6 records in table fish
4 records in table dogs
NDBT_ProgramExit: 0 - OK
ndb_show_tables displays a list of all
NDB
database objects in the cluster. By
default, this includes not only both user-created tables and
NDB
system tables, but
NDB
-specific indexes, and internal
triggers, as well.
Usage:
ndb_show_tables [-c connect_string
]
Additional Options:
Specifies the number of times the utility should execute. This is 1 when this option is not specified, but if you do use the option, you must supply an integer argument for it.
Using this option causes the output to be in a format
suitable for use with LOAD DATA INFILE
.
Can be used to restrict the output to one type of object, specified by an integer type code as shown here:
1: System table
2: User-created table
3: Unique hash index
Any other value causes all NDB
database
objects to be listed (the default).
If specified, this causes unqualified object names to be displayed.
Only user-created Cluster tables may be accessed from MySQL;
system tables such as SYSTAB_0
are not
visible to mysqld. However, you can
examine the contents of system tables using
NDB
API applications such as
ndb_select_all (see
Section 16.10.11, “ndb_select_all — Print Rows from NDB Table”).
This is a Perl script that can be used to estimate the amount
of space that would be required by a MySQL database if it were
converted to use the NDBCluster
storage
engine. Unlike the other utilities discussed in this section,
it does not require access to a MySQL Cluster (in fact, there
is no reason for it to do so). However, it does need to access
the MySQL server on which the database to be tested resides.
Requirements:
A running MySQL server. The server instance does not have to provide support for MySQL Cluster.
A working installation of Perl.
The DBI
and
HTML::Template
modules, both of which
can be obtained from CPAN if they are not already part of
your Perl installation. (Many Linux and other operating
system distributions provide their own packages for one or
both of these libraries.)
The ndb_size.tmpl
template file,
which you should be able to find in the
share/mysql
directory of your MySQL
installation. This file should be copied or moved into the
same directory as ndb_size.pl
—
if it is not there already — before running the
script.
A MySQL user account having the necessary privileges. If
you do not wish to use an existing account, then creating
one using GRANT USAGE ON
—
where db_name
.*db_name
is the name of
the database to be examined — is sufficient for this
purpose.
ndb_size.pl
and
ndb_size.tmpl
can also be found in the
MySQL sources in storage/ndb/tools
. If
these files are not present in your MySQL installation, you
can obtain them from the
MySQLForge
project page.
Usage:
perl ndb_size.pldb_name
hostname
username
password
>file_name
.html
The command shown connects to the MySQL server at
hostname
using the account of the
user username
having the password
password
, analyses all of the
tables in database db_name
, and
generates a report in HTML format which is directed to the
file
.
(Without the redirection, the output is sent to
file_name
.htmlstdout
.) This figure shows partial sample
output as viewed in a Web browser:
The output from this script includes:
Minimum values for the DataMemory
,
IndexMemory
,
MaxNoOfTables
,
MaxNoOfAttributes
,
MaxNoOfOrderedIndexes
,
MaxNoOfUniqueHashIndexes
, and
MaxNoOfTriggers
configuration
parameters required to accommodate the tables analysed.
Memory requirements for all of the tables, attributes, ordered indexes, and unique hash indexes defined in the database.
The IndexMemory
and
DataMemory
required per table and table
row.
ndb_waiter repeatedly (each 100
milliseconds) prints out the status of all cluster data nodes
until either the cluster reaches a given status or the
--timeout
limit is exceeded, then exits. By
default, it waits for the cluster to achieve
STARTED
status, in which all nodes have
started and connected to the cluster. This can be overridden
using the --no-contact
and
--not-started
options (see
Additional
Options).
The node states reported by this utility are as follows:
NO_CONTACT
: The node cannot be
contacted.
UNKNOWN
: The node can be contacted, but
its status is not yet known. Usually, this means that the
node has received a START
or
RESTART
command from the management
server, but has not yet acted on it.
NOT_STARTED
: The node has stopped, but
remains in contact with the cluster. This is seen when
restarting the node using the management client's
RESTART
command.
STARTING
: The node's
ndbd process has started, but the node
has not yet joined the cluster.
STARTED
: The node is operational, and
has joined the cluster.
SHUTTING_DOWN
: The node is shutting
down.
SINGLE USER MODE
: This is shown for all
cluster data nodes when the cluster is in single user
mode.
Usage:
ndb_waiter [-c connect_string
]
Instead of waiting for the STARTED
state, ndb_waiter continues running
until the cluster reaches NO_CONTACT
status before exiting.
Instead of waiting for the STARTED
state, ndb_waiter continues running
until the cluster reaches NOT_STARTED
status before exiting.
Time to wait. The program exits if the desired state is not achieved within this number of seconds. The default is 120 seconds (1200 reporting cycles).
Sample Output.
Shown here is the output from ndb_waiter
when run against a 4-node cluster in which two nodes have
been shut down and then started again manually. Duplicate
reports (indicated by “...
”)
are omitted.
shell> ./ndb_waiter -c localhost
Connecting to mgmsrv at (localhost)
State node 1 STARTED
State node 2 NO_CONTACT
State node 3 STARTED
State node 4 NO_CONTACT
Waiting for cluster enter state STARTED
...
State node 1 STARTED
State node 2 UNKNOWN
State node 3 STARTED
State node 4 NO_CONTACT
Waiting for cluster enter state STARTED
...
State node 1 STARTED
State node 2 STARTING
State node 3 STARTED
State node 4 NO_CONTACT
Waiting for cluster enter state STARTED
...
State node 1 STARTED
State node 2 STARTING
State node 3 STARTED
State node 4 UNKNOWN
Waiting for cluster enter state STARTED
...
State node 1 STARTED
State node 2 STARTING
State node 3 STARTED
State node 4 STARTING
Waiting for cluster enter state STARTED
...
State node 1 STARTED
State node 2 STARTED
State node 3 STARTED
State node 4 STARTING
Waiting for cluster enter state STARTED
...
State node 1 STARTED
State node 2 STARTED
State node 3 STARTED
State node 4 STARTED
Waiting for cluster enter state STARTED
NDBT_ProgramExit: 0 - OK
If no connectstring is specified, then
ndb_waiter tries to connect to a
management on localhost
, and reports
Connecting to mgmsrv at (null)
.
Even before design of NDB Cluster
began in 1996,
it was evident that one of the major problems to be encountered in
building parallel databases would be communication between the nodes
in the network. For this reason, NDB Cluster
was
designed from the very beginning to allow for the use of a number of
different data transport mechanisms. In this Manual, we use the term
transporter for these.
The MySQL Cluster codebase includes support for four different transporters:
TCP/IP using 100 Mbps or gigabit Ethernet, as discussed in Section 16.3.4.7, “Cluster TCP/IP Connections”.
Direct (machine-to-machine) TCP/IP; although this transporter uses the same TCP/IP protocol as mentioned in the previous item, it requires setting up the hardware differently and is configured differently as well. For this reason, it is considered a separate transport mechanism for MySQL Cluster. See Section 16.3.4.8, “TCP/IP Connections Using Direct Connections”, for details.
Shared memory (SHM). For more information about SHM, see Section 16.3.4.9, “Shared-Memory Connections”.
Scalable Coherent Interface (SCI), as described in the next section of this chapter, Section 16.3.4.10, “SCI Transport Connections”.
Most users today employ TCP/IP over Ethernet because it is ubiquitous. TCP/IP is also by far the best-tested transporter for use with MySQL Cluster.
We are working to make sure that communication with the ndbd process is made in “chunks” that are as large as possible because this benefits all types of data transmission.
For users who desire it, it is also possible to use cluster interconnects to enhance performance even further. There are two ways to achieve this: Either a custom transporter can be designed to handle this case, or you can use socket implementations that bypass the TCP/IP stack to one extent or another. We have experimented with both of these techniques using the SCI (Scalable Coherent Interface) technology developed by Dolphin.
In this section, we show how to adapt a cluster configured for normal TCP/IP communication to use SCI Sockets instead. This documentation is based on SCI Sockets version 2.3.0 as of 01 October 2004.
Prerequisites. Any machines with which you wish to use SCI Sockets must be equipped with SCI cards.
No special builds (other than the -max
builds)
are needed for SCI Sockets because it uses normal TCP/IP socket
calls which are already available in MySQL Cluster. However, SCI
Sockets are currently supported only on the Linux 2.4 and 2.6
kernels. For other operating systems, you can use SCI
Transporters, but this requires that the server be built using
--with-ndb-sci=/opt/DIS
.
Prior to MySQL 5.0.44, there were issues with building MySQL
Cluster with SCI support (see Bug#25470), but these have been
resolved due to work contributed by Dolphin International. SCI
Sockets are now correctly supported for MySQL Cluster using the
-max
builds, and versions of MySQL Cluster with
SCI Transporter support can be built using either of
compile-amd64-max-sci or
compile-pentium64-max-sci. Both of these build
scripts can be found in the BUILD
directory
of the MySQL 5.0 source; it should not be difficult
to adapt them for other platforms.
There are essentially four requirements for SCI Sockets:
Building the SCI Socket libraries.
Installation of the SCI Socket kernel libraries.
Installation of one or two configuration files.
The SCI Socket kernel library must be enabled either for the entire machine or for the shell where the MySQL Cluster processes are started.
This process needs to be repeated for each machine in the cluster where you plan to use SCI Sockets for inter-node communication.
Two packages need to be retrieved to get SCI Sockets working:
The source code package containing the DIS support libraries for the SCI Sockets libraries.
The source code package for the SCI Socket libraries themselves.
Currently, these are available only in source code format. The
latest versions of these packages at the time of this writing were
available as (respectively)
DIS_GPL_2_5_0_SEP_10_2004.tar.gz
and
SCI_SOCKET_2_3_0_OKT_01_2004.tar.gz
. You
should be able to find these (or possibly newer versions) at
http://www.dolphinics.no/support/downloads.html.
Package Installation. Once you have obtained the library packages, the next step is to unpack them into appropriate directories, with the SCI Sockets library unpacked into a directory below the DIS code. Next, you need to build the libraries. This example shows the commands used on Linux/x86 to perform this task:
shell>tar xzf DIS_GPL_2_5_0_SEP_10_2004.tar.gz
shell>cd DIS_GPL_2_5_0_SEP_10_2004/src/
shell>tar xzf ../../SCI_SOCKET_2_3_0_OKT_01_2004.tar.gz
shell>cd ../adm/bin/Linux_pkgs
shell>./make_PSB_66_release
It is possible to build these libraries for some 64-bit procesors. To build the libraries for Opteron CPUs using the 64-bit extensions, run make_PSB_66_X86_64_release rather than make_PSB_66_release. If the build is made on an Itanium machine, you should use make_PSB_66_IA64_release. The X86-64 variant should work for Intel EM64T architectures but this has not yet (to our knowledge) been tested.
Once the build process is complete, the compiled libraries will be
found in a zipped tar file with a name along the lines of
DIS-
.
It is now time to install the package in the proper place. In this
example we will place the installation in
<operating-system>
-time
-date
/opt/DIS
. You most likely need to run the
following as the system root
user.
shell>cp DIS_Linux_2.4.20-8_181004.tar.gz /opt/
shell>cd /opt
shell>tar xzf DIS_Linux_2.4.20-8_181004.tar.gz
shell>mv DIS_Linux_2.4.20-8_181004 DIS
Network Configuration. Now that all the libraries and binaries are in their proper place, we need to ensure that the SCI cards have proper node IDs within the SCI address space.
It is also necessary to decide on the network structure before proceeding. There are three types of network structures which can be used in this context:
A simple one-dimensional ring
One or more SCI switches with one ring per switch port
A two- or three-dimensional torus.
Each of these topologies has its own method for providing node IDs. We discuss each of them in brief.
A simple ring uses node IDs which are non-zero multiples of 4: 4, 8, 12,...
The next possibility uses SCI switches. An SCI switch has 8 ports, each of which can support a ring. It is necessary to make sure that different rings use different node ID spaces. In a typical configuration, the first port uses node IDs below 64 (4 – 60), the next 64 node IDs (68 – 124) are assigned to the next port, and so on, with node IDs 452 – 508 being assigned to the eighth port.
Two- and three-dimensional torus network structures take into account where each node is located in each dimension, incrementing by 4 for each node in the first dimension, by 64 in the second dimension, and (where applicable) by 1024 in the third dimension. See Dolphin's Web site for more thorough documentation.
In our testing we have used switches, although most large cluster installations use 2- or 3-dimensional torus structures. The advantage provided by switches is that, with dual SCI cards and dual switches, it is possible to build with relative ease a redundant network where the average failover time on the SCI network is on the order of 100 microseconds. This is supported by the SCI transporter in MySQL Cluster and is also under development for the SCI Socket implementation.
Failover for the 2D/3D torus is also possible but requires sending out new routing indexes to all nodes. However, this requires only 100 milliseconds or so to complete and should be acceptable for most high-availability cases.
By placing cluster data nodes properly within the switched architecture, it is possible to use 2 switches to build a structure whereby 16 computers can be interconnected and no single failure can hinder more than one of them. With 32 computers and 2 switches it is possible to configure the cluster in such a manner that no single failure can cause the loss of more than two nodes; in this case, it is also possible to know which pair of nodes is affected. Thus, by placing the two nodes in separate node groups, it is possible to build a “safe” MySQL Cluster installation.
To set the node ID for an SCI card use the following command in
the /opt/DIS/sbin
directory. In this example,
-c 1
refers to the number of the SCI card (this
is always 1 if there is only 1 card in the machine); -a
0
refers to adapter 0; and 68
is the
node ID:
shell> ./sciconfig -c 1 -a 0 -n 68
If you have multiple SCI cards in the same machine, you can
determine which card has which slot by issuing the following
command (again we assume that the current working directory is
/opt/DIS/sbin
):
shell> ./sciconfig -c 1 -gsn
This will give you the SCI card's serial number. Then repeat this
procedure with -c 2
, and so on, for each card in
the machine. Once you have matched each card with a slot, you can
set node IDs for all cards.
After the necessary libraries and binaries are installed, and the
SCI node IDs are set, the next step is to set up the mapping from
hostnames (or IP addresses) to SCI node IDs. This is done in the
SCI sockets configuration file, which should be saved as
/etc/sci/scisock.conf
. In this file, each SCI
node ID is mapped through the proper SCI card to the hostname or
IP address that it is to communicate with. Here is a very simple
example of such a configuration file:
#host #nodeId alpha 8 beta 12 192.168.10.20 16
It is also possible to limit the configuration so that it applies
only to a subset of the available ports for these hosts. An
additional configuration file
/etc/sci/scisock_opt.conf
can be used to
accomplish this, as shown here:
#-key -type -values EnablePortsByDefault yes EnablePort tcp 2200 DisablePort tcp 2201 EnablePortRange tcp 2202 2219 DisablePortRange tcp 2220 2231
Driver Installation. With the configuration files in place, the drivers can be installed.
First, the low-level drivers and then the SCI socket driver need to be installed:
shell>cd DIS/sbin/
shell>./drv-install add PSB66
shell>./scisocket-install add
If desired, the installation can be checked by invoking a script which verifies that all nodes in the SCI socket configuration files are accessible:
shell>cd /opt/DIS/sbin/
shell>./status.sh
If you discover an error and need to change the SCI socket configuration, it is necessary to use ksocketconfig to accomplish this task:
shell>cd /opt/DIS/util
shell>./ksocketconfig -f
Testing the setup. To ensure that SCI sockets are actually being used, you can employ the latency_bench test program. Using this utility's server component, clients can connect to the server to test the latency of the connection. Determining whether SCI is enabled should be fairly simple from observing the latency.
Before using latency_bench, it is necessary
to set the LD_PRELOAD
environment variable as
shown later in this section.
To set up a server, use the following:
shell>cd /opt/DIS/bin/socket
shell>./latency_bench -server
To run a client, use latency_bench again,
except this time with the -client
option:
shell>cd /opt/DIS/bin/socket
shell>./latency_bench -client
server_hostname
SCI socket configuration should now be complete and MySQL Cluster ready to use both SCI Sockets and the SCI transporter (see Section 16.3.4.10, “SCI Transport Connections”).
Starting the cluster.
The next step in the process is to start MySQL Cluster. To
enable usage of SCI Sockets it is necessary to set the
environment variable LD_PRELOAD
before
starting ndbd, mysqld, and
ndb_mgmd. This variable should point to the
kernel library for SCI Sockets.
To start ndbd in a bash shell, do the following:
bash-shell>export LD_PRELOAD=/opt/DIS/lib/libkscisock.so
bash-shell>ndbd
In a tcsh environment the same thing can be accomplished with:
tcsh-shell>setenv LD_PRELOAD=/opt/DIS/lib/libkscisock.so
tcsh-shell>ndbd
MySQL Cluster can use only the kernel variant of SCI Sockets.
The ndbd process has a number of simple constructs which are used to access the data in a MySQL Cluster. We have created a very simple benchmark to check the performance of each of these and the effects which various interconnects have on their performance.
There are four access methods:
Primary key access. This is access of a record through its primary key. In the simplest case, only one record is accessed at a time, which means that the full cost of setting up a number of TCP/IP messages and a number of costs for context switching are borne by this single request. In the case where multiple primary key accesses are sent in one batch, those accesses share the cost of setting up the necessary TCP/IP messages and context switches. If the TCP/IP messages are for different destinations, additional TCP/IP messages need to be set up.
Unique key access. Unique key accesses are similar to primary key accesses, except that a unique key access is executed as a read on an index table followed by a primary key access on the table. However, only one request is sent from the MySQL Server, and the read of the index table is handled by ndbd. Such requests also benefit from batching.
Full table scan. When no indexes exist for a lookup on a table, a full table scan is performed. This is sent as a single request to the ndbd process, which then divides the table scan into a set of parallel scans on all cluster ndbd processes. In future versions of MySQL Cluster, an SQL node will be able to filter some of these scans.
Range scan using ordered index
When an ordered index is used, it performs a scan in the same manner as the full table scan, except that it scans only those records which are in the range used by the query transmitted by the MySQL server (SQL node). All partitions are scanned in parallel when all bound index attributes include all attributes in the partitioning key.
To check the base performance of these access methods, we have developed a set of benchmarks. One such benchmark, testReadPerf, tests simple and batched primary and unique key accesses. This benchmark also measures the setup cost of range scans by issuing scans returning a single record. There is also a variant of this benchmark which uses a range scan to fetch a batch of records.
In this way, we can determine the cost of both a single key access and a single record scan access, as well as measure the impact of the communication media used, on base access methods.
In our tests, we ran the base benchmarks for both a normal transporter using TCP/IP sockets and a similar setup using SCI sockets. The figures reported in the following table are for small accesses of 20 records per access. The difference between serial and batched access decreases by a factor of 3 to 4 when using 2KB records instead. SCI Sockets were not tested with 2KB records. Tests were performed on a cluster with 2 data nodes running on 2 dual-CPU machines equipped with AMD MP1900+ processors.
Access Type | TCP/IP Sockets | SCI Socket |
Serial pk access | 400 microseconds | 160 microseconds |
Batched pk access | 28 microseconds | 22 microseconds |
Serial uk access | 500 microseconds | 250 microseconds |
Batched uk access | 70 microseconds | 36 microseconds |
Indexed eq-bound | 1250 microseconds | 750 microseconds |
Index range | 24 microseconds | 12 microseconds |
We also performed another set of tests to check the performance of SCI Sockets vis-à-vis that of the SCI transporter, and both of these as compared with the TCP/IP transporter. All these tests used primary key accesses either serially and multi-threaded, or multi-threaded and batched.
The tests showed that SCI sockets were about 100% faster than TCP/IP. The SCI transporter was faster in most cases compared to SCI sockets. One notable case occurred with many threads in the test program, which showed that the SCI transporter did not perform very well when used for the mysqld process.
Our overall conclusion was that, for most benchmarks, using SCI sockets improves performance by approximately 100% over TCP/IP, except in rare instances when communication performance is not an issue. This can occur when scan filters make up most of processing time or when very large batches of primary key accesses are achieved. In that case, the CPU processing in the ndbd processes becomes a fairly large part of the overhead.
Using the SCI transporter instead of SCI Sockets is only of interest in communicating between ndbd processes. Using the SCI transporter is also only of interest if a CPU can be dedicated to the ndbd process because the SCI transporter ensures that this process will never go to sleep. It is also important to ensure that the ndbd process priority is set in such a way that the process does not lose priority due to running for an extended period of time, as can be done by locking processes to CPUs in Linux 2.6. If such a configuration is possible, the ndbd process will benefit by 10–70% as compared with using SCI sockets. (The larger figures will be seen when performing updates and probably on parallel scan operations as well.)
There are several other optimized socket implementations for computer clusters, including Myrinet, Gigabit Ethernet, Infiniband and the VIA interface. We have tested MySQL Cluster so far only with SCI sockets. See Section 16.11.1, “Configuring MySQL Cluster to use SCI Sockets” for information on how to set up SCI sockets using ordinary TCP/IP for MySQL Cluster.
In the sections that follow, we discuss known limitations in MySQL
5.0 Cluster releases as compared with the features
available when using the MyISAM
and
InnoDB
storage engines. Currently, there are no
plans to address these in coming releases of MySQL 5.0;
however, we will attempt to supply fixes for these issues in
subsequent release series. If you check the “Cluster”
category in the MySQL bugs database at
http://bugs.mysql.com, you can find known bugs which
(if marked “5.0”) we intend to correct in
upcoming releases of MySQL 5.0.
This information is intended to be complete with respect to the conditions just set forth. You can report any discrepancies that you encounter to the MySQL bugs database using the instructions given in Section 1.7, “How to Report Bugs or Problems”. If we do not plan to fix the problem in MySQL 5.0, we will add it to the list.
See Section 16.12.10, “Previous MySQL Cluster Issues Resolved in MySQL 5.0” for a list of issues in MySQL Cluster in MySQL 4.1 that have been resolved in the current version.
Some SQL statements relating to certain MySQL features produce
errors when used with NDB
tables, as described
in the following list:
Temporary tables.
Temporary tables are not supported. Trying either to
create a temporary table that uses the
NDB
storage engine or to alter an
existing temporary table to use NDB
fails with the error Table storage engine
'ndbcluster' does not support the create option
'TEMPORARY'.
Indexes and keys in NDB
tables.
Keys and indexes on MySQL Cluster tables are subject to
the following limitations:
TEXT
and BLOB
columns.
You cannot create indexes on
NDB
table columns that use any
of the TEXT
or
BLOB
data types.
FULLTEXT
indexes.
The NDB
storage engine does not
support FULLTEXT
indexes, which
are possible for MyISAM
tables
only.
However, you can create indexes on
VARCHAR
columns of
NDB
tables.
BIT
columns.
A BIT
column cannot be a
primary key, unique key, or index, nor can it be
part of a composite primary key, unique key, or
index.
AUTO_INCREMENT
columns.
Like other MySQL storage engines, the
NDB
storage engine can handle a
maximum of one AUTO_INCREMENT
column per table. However, in the case of a
Cluster table with no explicit primary key, an
AUTO_INCREMENT
column is
automatically defined and used as a
“hidden” primary key. For this
reason, you cannot define a table that has an
explicit AUTO_INCREMENT
column
unless that column is also declared using the
PRIMARY KEY
option. Attempting
to create a table with an
AUTO_INCREMENT
column that is
not the table's primary key, and using the
NDB
storage engine, fails with
an error.
MySQL Cluster and geometry data types.
Geometry datatypes (WKT
and
WKB
) are supported in
NDB
tables in MySQL 5.0.
However, spatial indexes are not supported.
In this section, we list limits found in MySQL Cluster that either differ from limits found in, or that are not found in, standard MySQL.
Memory usage and recovery.
Memory comsumed when data is inserted into an
NDB
table is not automatically
recovered when deleted, as it is with other storage
engines. Instead, the following rules hold true:
A DELETE
statement on an
NDB
table makes the memory
formerly used by the deleted rows available for
re-use by inserts on the same table only. This
memory cannot be used by other
NDB
tables.
A DROP TABLE
or
TRUNCATE
operation on an
NDB
table frees the memory that
was used by this table for re-use by any
NDB
table, either by the same
table or by another NDB
table.
Recall that TRUNCATE
drops and
re-creates the table. See
Section 12.2.9, “TRUNCATE
Syntax”.
Memory freed by DELETE
operations
but still allocated to a specific table can also be
made available for general re-use by performing a
rolling restart of the cluster. See
Section 16.5.1, “Performing a Rolling Restart of the Cluster”.
Limits imposed by the cluster's configuration. A number of hard limits exist which are configurable, but available main memory in the cluster sets limits. See the complete list of configuration parameters in Section 16.3.4, “Configuration File”. Most configuration parameters can be upgraded online. These hard limits include:
Database memory size and index memory size
(DataMemory
and
IndexMemory
,
respectively).
DataMemory
is allocated
as 32KB pages. As each
DataMemory
page is used,
it is assigned to a specific table; once
allocated, this memory cannot be freed
except by dropping the table.
See
Section 16.3.4.5, “Defining Data Nodes”,
for further information about
DataMemory
and
IndexMemory
.
The maximum number of operations that can be
performed per transaction is set using the
configuration parameters
MaxNoOfConcurrentOperations
and
MaxNoOfLocalOperations
.
Bulk loading, TRUNCATE
TABLE
, and ALTER
TABLE
are handled as special
cases by running multiple transactions,
and so are not subject to this limitation.
Different limits related to tables and
indexes. For example, the maximum number of
ordered indexes per table is determined by
MaxNoOfOrderedIndexes
.
Memory usage.
All Cluster table rows are of fixed length. This
means (for example) that if a table has one or
more VARCHAR
fields containing
only relatively small values, more memory and disk
space is required when using the
NDB
storage engine than would
be the case for the same table and data using the
MyISAM
engine. (In other words,
in the case of a VARCHAR
column, the column requires the same amount of
storage as a CHAR
column of the
same size.)
Node and data object maximums. The following limits apply to numbers of cluster nodes and metadata objects:
The maximum number of data nodes is 48.
A data node must have a node ID in the range of 1‐49, inclusive. (Management and API nodes may use any integer in the range of 1‐63 inclusive as a node ID.)
The total maximum number of nodes in a MySQL Cluster is 63. This number includes all SQL nodes (MySQL Servers), API nodes (applications accessing the cluster other than MySQL servers), data nodes, and management servers.
The maximum number of metadata objects in MySQL 5.0 Cluster is 20320. This limit is hard-coded.
A number of limitations exist in MySQL Cluster with regard to the handling of transactions. These include the following:
Transaction isolation level.
The NDBCLUSTER
storage engine supports
only the READ COMMITTED
transaction
isolation level. (InnoDB
, for example,
supports READ COMMITTED
, READ
UNCOMMITTED
, REPEATABLE READ
,
and SERIALIZABLE
.) See
Section 16.9.5, “Backup Troubleshooting”,
for information on how this can affect backing up and
restoring Cluster databases.)
If a SELECT
from a Cluster table
includes a BLOB
or
TEXT
column, the READ
COMMITTED
transaction isolation level is
converted to a read with read lock. This is done to
guarantee consistency, due to the fact that parts of
the values stored in columns of these types are
actually read from a separate table.
Rollbacks. There is no partial rollback of transactions. A duplicate key or similar error rolls back the entire transaction.
Transactions and memory usage. As noted elsewhere in this chapter, MySQL Cluster does not handle large transactions well; it is better to perform a number of small transactions with a few operations each than to attempt a single large transaction containing a great many operations. Among other considerations, large transactions require very large amounts of memory. Because of this, the transactional behaviour of a number of MySQL statements is effected as described in the following list:
TRUNCATE
is not transactional
when used on NDB
tables. If a
TRUNCATE
fails to empty the
table, then it must be re-run until it is
successful.
DELETE FROM
(even with no
WHERE
clause)
is transactional. For tables
containing a great many rows, you may find that
performance is improved by using several
DELETE FROM ... LIMIT ...
statements to “chunk” the delete
operation. If your objective is to empty the table,
then you may wish to use TRUNCATE
instead.
LOAD DATA
statements.
LOAD DATA INFILE
is not
transactional when used on NDB
tables.
When executing a LOAD DATA
INFILE
statement, the
NDB
engine performs commits
at irregular intervals that enable better
utilization of the communication network. It
is not possible to know ahead of time when
such commits take place.
LOAD DATA FROM MASTER
is not
supported in MySQL Cluster.
ALTER TABLE
and transactions.
When copying an NDB
table as
part of an ALTER TABLE
, the
creation of the copy is non-transactional. (In any
case, this operation is rolled back when the copy
is deleted.)
Starting, stopping, or restarting a node may give rise to temporary errors causing some transactions to fail. These include the following cases:
Temporary errors. When first starting a node, it is possible that you may see Error 1204 Temporary failure, distribution changed and similar temporary errors.
Errors due to node failure. The stopping or failure of any data node can result in a number of different node failure errors. (However, there should be no aborted transactions when performing a planned shutdown of the cluster.)
In either of these cases, any errors that are generated must be handled within the application. This should be done by retrying the transaction.
See also Section 16.12.2, “Limits and Differences from Standard MySQL Limits”.
Some database objects such as tables and indexes have different
limitations when using the NDBCLUSTER
storage
engine:
Identifiers.
Database names, table names and attribute names cannot be
as long in NDB
tables as when using
other table handlers. Attribute names are truncated to 31
characters, and if not unique after truncation give rise
to errors. Database names and table names can total a
maximum of 122 characters. In other words, the maximum
length for an NDB
table name is 122
characters, less the number of characters in the name of
the database of which that table is a part.
Table names containing special characters.
NDB
tables whose names contain
characters other than letters, numbers, dashes, and
underscores and which are created on one SQL node may not
be discovered correctly by other SQL nodes. (Bug#31470)
Number of tables. The maximum number of tables in a Cluster database in MySQL 5.0 is limited to 1792.
Attributes per table. The maximum number of attributes (that is, columns and indexes) per table is limited to 128.
Attributes per key. The maximum number of attributes per key is 32.
Row size.
The maximum permitted size of any one row is 8KB. Note
that each BLOB
or
TEXT
column contributes 256 + 8 = 264
bytes towards this total.
A number of features supported by other storage engines are not
supported for NDB
tables. Trying to use any of
these features in MySQL Cluster does not cause errors in or of
itself; however, errors may occur in applications that expects the
features to be supported or enforced:
Foreign key constraints.
The foreign key construct is ignored, just as it is in
MyISAM
tables.
OPTIMIZE
operations.
OPTIMIZE
operations are not supported.
LOAD TABLE ... FROM MASTER
.
LOAD TABLE ... FROM MASTER
is not
supported.
Savepoints and rollbacks.
Savepoints and rollbacks to savepoints are ignored as in
MyISAM
.
Durability of commits. There are no durable commits on disk. Commits are replicated, but there is no guarantee that logs are flushed to disk on commit.
Replication. Replication is not supported.
See Section 16.12.3, “Limits Relating to Transaction Handling”,
for more information relating to limitations on transaction
handling in NDB
.
The following performance issues are specific to or especially pronounced in MySQL Cluster:
Range scans.
There are query performance issues due to sequential
access to the NDB
storage engine; it is
also relatively more expensive to do many range scans than
it is with either MyISAM
or
InnoDB
.
Reliability of Records in range
.
The Records in range
statistic is
available but is not completely tested or officially
supported. This may result in non-optimal query plans in
some cases. If necessary, you can employ USE
INDEX
or FORCE INDEX
to alter
the execution plan. See Section 12.2.7.2, “Index Hint Syntax”, for
more information on how to do this.
Unique hash indexes.
Unique hash indexes created with USING
HASH
cannot be used for accessing a table if
NULL
is given as part of the key.
The following are limitations specific to the
NDBCLUSTER
storage engine:
Machine architecture. The following issues relate to physical architecture of cluster hosts:
All machines used in the cluster must have the same architecture. That is, all machines hosting nodes must be either big-endian or little-endian, and you cannot use a mixture of both. For example, you cannot have a management node running on a PowerPC which directs a data node that is running on an x86 machine. This restriction does not apply to machines simply running mysql or other clients that may be accessing the cluster's SQL nodes.
Adding and dropping of data nodes. Online adding or dropping of data nodes is not currently possible. In such cases, the entire cluster must be restarted.
Backup and restore between architectures. It is also not possible to perform a Cluster backup and restore between different architectures. For example, you cannot back up a cluster running on a big-endian platform and then restore from that backup to a cluster running on a little-endian system. (Bug#19255)
Online schema changes.
It is not possible to make online schema changes such as
those accomplished using ALTER TABLE
or
CREATE INDEX
, as the NDB
Cluster
engine does not support autodiscovery of
such changes. (However, you can import or create a table
that uses a different storage engine, and then convert it
to NDB
using ALTER TABLE
. In such a case, you must
issue a tbl_name
ENGINE=NDBCLUSTERFLUSH TABLES
statement to force
the cluster to pick up the change.)
Binary logging. MySQL Cluster has the following limitations or restrictions with regard to binary logging:
SQL_LOG_BIN
has no effect on data
operations; however, it is supported for schema
operations.
MySQL Cluster cannot produce a binlog for tables
having BLOB
columns but no
primary key.
Only the following schema operations are logged in a cluster binlog which is not on the mysqld executing the statement:
CREATE TABLE
ALTER TABLE
DROP TABLE
CREATE DATABASE
/
CREATE SCHEMA
DROP DATABASE
/
DROP SCHEMA
See also Section 16.12.9, “Limitations Relating to Multiple Cluster Nodes”.
Multiple SQL nodes.
The following are issues relating to the use of multiple MySQL
servers as MySQL Cluster SQL nodes, and are specific to the
NDBCLUSTER
storage engine:
No distributed table locks.
A LOCK TABLES
works only for the SQL
node on which the lock is issued; no other SQL node in
the cluster “sees” this lock. This is also
true for a lock issued by any statement that locks
tables as part of its operations. (See next item for an
example.)
ALTER TABLE
operations.
ALTER TABLE
is not fully locking when
running multiple MySQL servers (SQL nodes). (As
discussed in the previous item, MySQL Cluster does not
support distributed table locks.)
Replication. MySQL replication will not work correctly if updates are done on multiple MySQL servers. However, if the database partitioning scheme is done at the application level and no transactions take place across these partitions, replication can be made to work.
Database autodiscovery.
Autodiscovery of databases is not supported for multiple
MySQL servers accessing the same MySQL Cluster. However,
autodiscovery of tables is supported in such cases. What
this means is that after a database named
db_name
is created or
imported using one MySQL server, you should issue a
CREATE DATABASE
statement
on each additional MySQL server that accesses the same
MySQL Cluster. (As of MySQL 5.0.2, you may also use
db_name
CREATE SCHEMA
.) Once this
has been done for a given MySQL server, that server
should be able to detect the database tables without
error.
db_name
DDL operations.
DDL operations (such as CREATE TABLE
or ALTER TABLE
) are not safe from
data node failures. If a data node fails while trying to
peform one of these, the data dictionary is locked and
no further DDL statements can be executed without
restarting the cluster.
Multiple management nodes. When using multiple management servers:
You must give nodes explicit IDs in connectstrings because automatic allocation of node IDs does not work across multiple management servers.
You must take extreme care to have the same configurations for all management servers. No special checks for this are performed by the cluster.
Prior to MySQL 5.0.14, all data nodes had to be restarted after bringing up the cluster in order for the management nodes to be able to see one another.
Multiple data node processes. While it is possible to run multiple cluster processes concurrently on a single host, it is not always advisable to do so for reasons of performance and high availability, as well as other considerations. In particular, in MySQL 5.0, we do not support for production use any MySQL Cluster deployment in which more than one ndbd process is run on a single physical machine.
We may support multiple data nodes per host in a future MySQL release, following additional testing. However, in MySQL 5.0, such configurations can be considered experimental only.
Multiple network addresses. Multiple network addresses per data node are not supported. Use of these is liable to cause problems: In the event of a data node failure, an SQL node waits for confirmation that the data node went down but never receives it because another route to that data node remains open. This can effectively make the cluster inoperable.
It is possible to use multiple network hardware
interfaces (such as Ethernet cards) for
a single data node, but these must be bound to the same
address. This also means that it not possible to use more
than one [tcp]
section per connection in
the config.ini
file. See
Section 16.3.4.7, “Cluster TCP/IP Connections”, for more
information.
The following Cluster limitations in MySQL 4.1 have been resolved in MySQL 5.0 as shown below:
Character set support.
The NDB Cluster
storage engine supports
all character sets and collations available in MySQL 5.0.
Character set directory.
Beginning with MySQL 5.0.21, it is possible to install MySQL
with Cluster support to a non-default location and change
the search path for font description files using either the
--basedir
or
--character-sets-dir
options. (Previously,
ndbd in MySQL 5.0 searched only the
default path — typically
/usr/local/mysql/share/mysql/charsets
— for character sets.)
Metadata objects. Prior to MySQL 5.0.6, the maximum number of metadata objects possible was 1600. Beginning with MySQL 5.0.6, this limit is increased to 20320.
Column indexes using prefixes. MySQL Cluster in MySQL 5.0 supports column indexes that make use of prefixes.
Query cache. Unlike the case in MySQL 4.1, the Cluster storage engine in MySQL 5.0 supports MySQL's query cache. See Section 7.5.4, “The MySQL Query Cache”.
IGNORE
and REPLACE
functionality.
In MySQL 5.0.19 and earlier, INSERT
IGNORE
, UPDATE IGNORE
, and
REPLACE
were supported only for primary
keys, but not for unique keys. It was possible to work
around this issue by removing the constraint, then dropping
the unique index, performing any inserts, and then adding
the unique index again.
This limitation was removed for INSERT
IGNORE
and REPLACE
in MySQL
5.0.20. (See Bug#17431.)
auto_increment_increment
and
auto_increment_offset
.
The auto_increment_increment
and
auto_increment_offset
server system
variables are supported for NDBCLUSTER
tables beginning with MySQL 5.0.46.
In this section, we discuss changes in the implementation of MySQL Cluster in MySQL 5.0 as compared to MySQL 4.1. We will also discuss our roadmap for further improvements to MySQL Cluster as currently planned for MySQL 5.1.
There are relatively few changes between the NDB Cluster storage engine implementations in MySQL 4.1 and in 5.0, so the upgrade path should be relatively quick and painless.
All significantly new features being developed for MySQL Cluster are going into the MySQL 5.1 and 5.2 trees. For information on changes in the Cluster implementations in MySQL versions 5.1 and later, see MySQL Cluster.
MySQL Cluster in versions 5.0.3-beta and later contains a number of new features that are likely to be of interest:
Condition pushdown. Consider the following query:
SELECT * FROM t1 WHERE non_indexed_attribute = 1;
This query uses a full table scan and the condition is
evaluated in the cluster's data nodes. Thus, it is not
necessary to send the records across the network for
evaluation. (That is, function transport is used, rather
than data transport.) Please note that this feature is
currently disabled by default (pending more thorough
testing), but it should work in most cases. This feature can
be enabled through the use of the SET
engine_condition_pushdown = On
statement.
Alternatively, you can run mysqld with
the this feature enabled by starting the MySQL server with
the --engine-condition-pushdown
option.
A major benefit of this change is that queries can be executed in parallel. This means that queries against non-indexed columns can run faster than previously by a factor of as much as 5 to 10 times, times the number of data nodes, because multiple CPUs can work on the query in parallel.
You can use EXPLAIN
to determine when
condition pushdown is being used. See
Section 12.3.2, “EXPLAIN
Syntax”.
Decreased IndexMemory
Usage: In MySQL 5.0, each record
consumes approximately 25 bytes of index memory, and every
unique index uses 25 bytes per record of index memory (in
addition to some data memory because these are stored in a
separate table). This is because the primary key is not stored
in the index memory anymore.
Query Cache Enabled for MySQL Cluster: See Section 7.5.4, “The MySQL Query Cache”, for information on configuring and using the query cache.
New optimizations. One optimization that merits particular attention is that a batched read interface is now used in some queries. For example, consider the following query:
SELECT * FROM t1 WHERE primary_key
IN (1,2,3,4,5,6,7,8,9,10);
This query will be executed 2 to 3 times more quickly than in previous MySQL Cluster versions due to the fact that all 10 key lookups are sent in a single batch rather than one at a time.
Limit On Number of Metadata
Objects: Beginning with MySQL 5.0.6, each Cluster
database may contain a maximum of 20320 metadata objects
— this includes database tables, system tables, indexes
and BLOB
values. (Previously, this number
was 1600.)
What is said here is a status report based on recent commits to the MySQL 5.1 source tree. It should be noted all 5.1 development is subject to change.
There are currently 4 major new features being developed for MySQL 5.1:
Integration of MySQL Cluster into MySQL replication: This will make it possible to update from any MySQL Server in the cluster and still have the MySQL Replication handled by one of the MySQL Servers in the cluster, with the state of the slave side remaining consistent with the cluster acting as the master.
Support for disk-based records: Records on disk will be supported. Indexed fields including the primary key hash index must still be stored in RAM but all other fields can be on disk.
Variable-sized records.
A column defined as VARCHAR(255)
currently uses 260 bytes of storage independent of what is
stored in any particular record. In MySQL 5.1 Cluster
tables, only the portion of the column actually taken up by
the record will be stored. This will make possible a
reduction in space requirements for such columns by a factor
of 5 in many cases.
User-defined partitioning.
Users will be able to define partitions based on columns
that are part of the primary key. The MySQL Server will be
able to discover whether it is possible to prune away some
of the partitions from the WHERE
clause.
Partitioning based on KEY
,
HASH
, RANGE
, and
LIST
handlers will be possible, as well
as subpartitioning. This feature should also be available
for many other handlers, and not only NDB
Cluster
.
In addition, we are working to increase the 8KB size limit for
rows containing columns of types other than
BLOB
or TEXT
in Cluster
tables. This is due to the fact that rows are currently fixed in
size and the page size is 32,768 bytes (minus 128 bytes for the
row header). Currently, this means that if we allowed more than
8KB per record, any remaining space (up to approximately 14,000
bytes) would be left empty. In MySQL 5.1, we plan to fix this
limitation so that using more than 8KB in a given row does not
result in the remainder of the page being wasted.
The following terms are useful to an understanding of MySQL Cluster or have specialized meanings when used in relation to it.
Cluster. In its generic sense, a cluster is a set of computers functioning as a unit and working together to accomplish a single task.
NDB Cluster
.
This is the storage engine used in MySQL to implement data
storage, retrieval, and management distributed among several
computers.
MySQL Cluster.
This refers to a group of computers working together using the
NDB
storage engine to support a distributed
MySQL database in a shared-nothing
architecture using in-memory
storage.
Configuration files. Text files containing directives and information regarding the cluster, its hosts, and its nodes. These are read by the cluster's management nodes when the cluster is started. See Section 16.3.4, “Configuration File”, for details.
Backup. A complete copy of all cluster data, transactions and logs, saved to disk or other long-term storage.
Restore. Returning the cluster to a previous state, as stored in a backup.
Checkpoint.
Generally speaking, when data is saved to disk, it is said
that a checkpoint has been reached. More specific to Cluster,
it is a point in time where all committed transactions are
stored on disk. With regard to the NDB
storage engine, there are two types of checkpoints which work
together to ensure that a consistent view of the cluster's
data is maintained:
Local Checkpoint (LCP). This is a checkpoint that is specific to a single node; however, LCP's take place for all nodes in the cluster more or less concurrently. An LCP involves saving all of a node's data to disk, and so usually occurs every few minutes. The precise interval varies, and depends upon the amount of data stored by the node, the level of cluster activity, and other factors.
Global Checkpoint (GCP). A GCP occurs every few seconds, when transactions for all nodes are synchronized and the redo-log is flushed to disk.
Cluster host. A computer making up part of a MySQL Cluster. A cluster has both a physical structure and a logical structure. Physically, the cluster consists of a number of computers, known as cluster hosts (or more simply as hosts. See also Node and Node group below.
Node. This refers to a logical or functional unit of MySQL Cluster, and is sometimes also referred to as a cluster node. In the context of MySQL Cluster, we use the term “node” to indicate a process rather than a physical component of the cluster. There are three node types required to implement a working MySQL Cluster:
Management nodes. Manages the other nodes within the MySQL Cluster. It provides configuration data to the other nodes; starts and stops nodes; handles network partitioning; creates backups and restores from them, and so forth.
SQL nodes. Instances of MySQL Server which serve as front ends to data kept in the cluster's data nodes. Clients desiring to store, retrieve, or update data can access an SQL node just as they would any other MySQL Server, employing the usual MySQL authentication methods and APIs; the underlying distribution of data between node groups is transparent to users and applications. SQL nodes access the cluster's databases as a whole without regard to the data's distribution across different data nodes or cluster hosts.
Data nodes. These nodes store the actual data. Table data fragments are stored in a set of node groups; each node group stores a different subset of the table data. Each of the nodes making up a node group stores a replica of the fragment for which that node group is responsible. Currently, a single cluster can support up to 48 data nodes total.
It is possible for more than one node to co-exist on a single machine. (In fact, it is even possible to set up a complete cluster on one machine, although one would almost certainly not want to do this in a production environment.) It may be helpful to remember that, when working with MySQL Cluster, the term host refers to a physical component of the cluster whereas a node is a logical or functional component (that is, a process).
Note Regarding Terms. In volder versions of the MySQL Cluster documentation, data nodes were sometimes referred to as “database nodes”. The term “storage nodes” has also been used. In addition, SQL nodes were sometimes known as “client nodes”. This older terminology has been deprecated to minimize confusion, and for this reason should be avoided. They are also often referred to as “API nodes” — an SQL node is actually an API node that provides an SQL interface to the cluster.
Node group. A set of data nodes. All data nodes in a node group contain the same data (fragments), and all nodes in a single group should reside on different hosts. It is possible to control which nodes belong to which node groups.
For more information, see Section 16.1.2, “MySQL Cluster Nodes, Node Groups, Replicas, and Partitions”.
Node failure. MySQL Cluster is not solely dependent upon the functioning of any single node making up the cluster; the cluster can continue to run if one or more nodes fail. The precise number of node failures that a given cluster can tolerate depends upon the number of nodes and the cluster's configuration.
Node restart. The process of restarting a failed cluster node.
Initial node restart. The process of starting a cluster node with its filesystem removed. This is sometimes used in the course of software upgrades and in other special circumstances.
System crash (or system failure). This can occur when so many cluster nodes have failed that the cluster's state can no longer be guaranteed.
System restart. The process of restarting the cluster and reinitializing its state from disk logs and checkpoints. This is required after either a planned or an unplanned shutdown of the cluster.
Fragment.
A portion of a database table; in the NDB
storage engine, a table is broken up into and stored as a
number of fragments. A fragment is sometimes also called a
“partition”; however, “fragment” is
the preferred term. Tables are fragmented in MySQL Cluster in
order to facilitate load balancing between machines and nodes.
Replica.
Under the NDB
storage engine, each table
fragment has number of replicas stored on other data nodes in
order to provide redundancy. Currently, there may be up four
replicas per fragment.
Transporter. A protocol providing data transfer between nodes. MySQL Cluster currently supports four different types of transporter connections:
TCP/IP. This is, of course, the familiar network protocol that underlies HTTP, FTP (and so on) on the Internet. TCP/IP can be used for both local and remote connections.
SCI. Scalable Coherent Interface is a high-speed protocol used in building multiprocessor systems and parallel-processing applications. Use of SCI with MySQL Cluster requires specialized hardware, as discussed in Section 16.11.1, “Configuring MySQL Cluster to use SCI Sockets”. For a basic introduction to SCI, see this essay at dolphinics.com.
SHM.
Unix-style shared
memory segments. Where
supported, SHM is used automatically to connect nodes
running on the same host. The
Unix
man page for shmop(2)
is a good
place to begin obtaining additional information about this
topic.
The cluster transporter is internal to the cluster. Applications using MySQL Cluster communicate with SQL nodes just as they do with any other version of MySQL Server (via TCP/IP, or through the use of Unix socket files or Windows named pipes). Queries can be sent and results retrieved using the standard MySQL client APIs.
NDB
.
This stands for Network
Database,
and refers to the storage engine used to enable MySQL Cluster.
The NDB
storage engine supports all the
usual MySQL data types and SQL statements, and is
ACID-compliant. This engine also provides full support for
transactions (commits and rollbacks).
Shared-nothing architecture. The ideal architecture for a MySQL Cluster. In a true shared-nothing setup, each node runs on a separate host. The advantage such an arrangement is that there no single host or node can act as single point of failure or as a performance bottle neck for the system as a whole.
In-memory storage. All data stored in each data node is kept in memory on the node's host computer. For each data node in the cluster, you must have available an amount of RAM equal to the size of the database times the number of replicas, divided by the number of data nodes. Thus, if the database takes up 1GB of memory, and you want to set up the cluster with four replicas and eight data nodes, a minimum of 500MB memory will be required per node. Note that this is in addition to any requirements for the operating system and any other applications that might be running on the host.
Table. As is usual in the context of a relational database, the term “table” denotes a set of identically structured records. In MySQL Cluster, a database table is stored in a data node as a set of fragments, each of which is replicated on additional data nodes. The set of data nodes replicating the same fragment or set of fragments is referred to as a node group.
Cluster programs. These are command-line programs used in running, configuring, and administering MySQL Cluster. They include both server daemons:
ndbd:
The data node daemon (runs a data node process)
ndb_mgmd:
The management server daemon (runs a management server process)
and client programs:
ndb_mgm:
The management client (provides an interface for executing management commands)
ndb_waiter:
Used to verify status of all nodes in a cluster
ndb_restore:
Restores cluster data from backup
For more about these programs and their uses, see Section 16.6, “Process Management in MySQL Cluster”.
Event log. MySQL Cluster logs events by category (startup, shutdown, errors, checkpoints, and so on), priority, and severity. A complete listing of all reportable events may be found in Section 16.7.3, “Event Reports Generated in MySQL Cluster”. Event logs are of two types:
Cluster log. Keeps a record of all desired reportable events for the cluster as a whole.
Node log. A separate log which is also kept for each individual node.
Under normal circumstances, it is necessary and sufficient to keep and examine only the cluster log. The node logs need be consulted only for application development and debugging purposes.