Chapter 19. MySQL Cluster

MySQL Cluster is a high-availability, high-redundancy version of MySQL adapted for the distributed computing environment. It uses the NDBCLUSTER 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.

19.1. MySQL Cluster Overview

19.1.1. MySQL Cluster Core Concepts
19.1.2. MySQL Cluster Nodes, Node Groups, Replicas, and Partitions

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 one or more processes which may include a MySQL server, a data node, a management server, and (possibly) 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 NDBCLUSTER 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.

19.1.1. MySQL Cluster Core Concepts

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.

Note

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 19.12.9, “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.

Important

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 19.1.2, “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.

19.1.2. MySQL Cluster Nodes, Node Groups, Replicas, and Partitions

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).
Note
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.

A MySQL Cluster, with 2 node groups having 2
nodes each

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.

Nodes required to keep a 2x2 cluster
viable

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.

19.2. Simple Multi-Computer How-To

19.2.1. Hardware, Software, and Networking
19.2.2. Multi-Computer Installation
19.2.3. Multi-Computer Configuration
19.2.4. Initial Startup
19.2.5. Loading Sample Data and Performing Queries
19.2.6. Safe Shutdown and Restart

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 19.3, “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 is to be set up with four nodes, each on a separate host, and each with a fixed network address on a typical Ethernet network 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.
Note
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 19.2.1, “Hardware, Software, and Networking”.)

19.2.1. 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. (It is possible to reduce this requirement using Disk Data tables, which were 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 platform, available via the MySQL software downloads page at http://dev.mysql.com/downloads/.

For communication between nodes, 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 19.8.1, “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 19.11, “Using High-Speed Interconnects with MySQL Cluster”, for more about this protocol and its use with MySQL Cluster.

19.2.2. Multi-Computer Installation

Each MySQL Cluster host computer running an SQL node 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-5.0.70-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-5.0.70-0.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-5.0.70-0.glibc23.i386.rpm), which supplies the MySQL Cluster data node binary (ndbd).
The NDB Cluster - Storage engine management RPM (for example, MySQL-ndb-management-5.0.70-0.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-5.0.70-0.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-5.0.70-0.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 19.10, “Cluster Utility Programs”.)

The MySQL version number in the RPM filenames (shown here as 5.0.70) 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 19.2.3, “Multi-Computer Configuration”.

Note

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-5.0.70-pc-linux-gnu-i686.tar.gz
shell> ln -s /usr/local/mysql-5.0.70-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 19.2.3, “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-5.0.70-0.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-5.0.70-0.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-5.0.70-pc-linux-gnu-i686.tar.gz
shell> cd mysql-5.0.70-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-5.0.70-0.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-5.0.70-0.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 19.2.3, “Multi-Computer Configuration”, we create configuration files for all of the nodes in our example Cluster.

19.2.3. Multi-Computer Configuration

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 19.3.4.2, “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.

Important

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 the 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)

Note

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 19.2.4, “Initial Startup”.

For more detailed information about the available MySQL Cluster configuration parameters and their uses, see Section 19.3.4, “Configuration File”, and Section 19.3, “MySQL Cluster Configuration”. For configuration of MySQL Cluster as relates to making backups, see Section 19.9.4, “Configuration for Cluster Backup”.

Note

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.

19.2.4. Initial Startup

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
ndb_mgmd must be told where to find its configuration file, using the -f or --config-file option. (See Section 19.6.3, “ndb_mgmd — The Management Server Process”, for details.)
For additional options which can be used with ndb_mgmd, see Section 19.6.5, “Command Options for MySQL Cluster Processes”.
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: 5.0.70, Nodegroup: 0, Master)
id=3    @192.168.0.40  (Version: 5.0.70, Nodegroup: 0)

[ndb_mgmd(MGM)] 1 node(s)
id=1    @192.168.0.10  (Version: 5.0.70)

[mysqld(SQL)]   1 node(s)
id=4   (Version: 5.0.70)

Note

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 19.2.5, “Loading Sample Data and Performing Queries”, for a brief discussion.

19.2.5. Loading Sample Data and Performing Queries

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 NDBCLUSTER storage engine. To specify this, use the ENGINE=NDB or ENGINE=NDBCLUSTER table option. You can add this option when creating the table:
```
CREATE TABLE tbl_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 NDBCLUSTER:
```
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 NDBCLUSTER storage engine automatically generates a hidden one.
Note
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=engine_name or ENGINE=engine_name with 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 NDBCLUSTER in MySQL 5.0 does not support autodiscovery of databases. (See Section 19.12, “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: 5.0.70

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 19.8.2, “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.

19.2.6. Safe Shutdown and Restart

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 19.6.5, “Command Options for MySQL Cluster Processes”, for more information about this option.) 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 &
```

In a production setting, it is usually not desirable to shut down the cluster completely. In many cases, even when making configuration changes, or performing upgrades to the cluster hardware or software (or both), which require shutting down individual host machines, it is possible to do so without shutting down the cluster as a whole by performing a rolling restart of the cluster. For more information about doing this, see Section 19.5.1, “Performing a Rolling Restart of the Cluster”.

19.3. MySQL Cluster Configuration

19.3.1. Building MySQL Cluster from Source Code
19.3.2. Installing the Cluster Software
19.3.3. Quick Test Setup of MySQL Cluster
19.3.4. Configuration File
19.3.5. Overview of Cluster Configuration Parameters
19.3.6. Configuring Parameters for Local Checkpoints

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 NDBCLUSTER 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 19.4.2, “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.

19.3.1. Building MySQL Cluster from Source Code

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 one of the MySQL Cluster public development trees, 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.

19.3.2. Installing the Cluster Software

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.

19.3.3. Quick Test Setup of MySQL Cluster

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

For command-line options which can be used when starting ndbd, see Section 19.6.5, “Command Options for MySQL Cluster Processes”.

By default, ndbd looks for the management server at localhost on port 1186.

Note

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: 5.0.70

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.

19.3.4. Configuration File

19.3.4.1. Basic Example Configuration
19.3.4.2. The Cluster Connectstring
19.3.4.3. Defining Cluster Computers
19.3.4.4. Defining the Management Server
19.3.4.5. Defining Data Nodes
19.3.4.6. Defining SQL and Other API Nodes
19.3.4.7. Cluster TCP/IP Connections
19.3.4.8. TCP/IP Connections Using Direct Connections
19.3.4.9. Shared-Memory Connections
19.3.4.10. SCI Transport Connections

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”.

19.3.4.1. Basic Example Configuration

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 19.3.4.2, “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

Important

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=path_name on the ndb_mgmd command line. If the configuration file is not specified, ndb_mgmd by default tries to read a file named 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.

Note

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 19.3.4.3, “Defining Cluster Computers”, for more information.
[ndbd]: Defines a cluster data node (ndbd process). See Section 19.3.4.5, “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 19.3.4.6, “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 19.3.4.4, “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 19.3.4.7, “Cluster TCP/IP Connections”, for information about available TCP/IP configuration parameters and how to use them. (You may also find Section 19.3.4.8, “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 19.3.4.9, “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 19.3.4.10, “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.

19.3.4.2. The Cluster Connectstring

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:
1. Set the NDB_CONNECTSTRING environment variable to contain the connectstring.
2. 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.

19.3.4.3. Defining Cluster Computers

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.

Id
This is an integer value, used to refer to the host computer elsewhere in the configuration file. This is not the same as the node ID.
HostName
This is the computer's hostname or IP address.

19.3.4.4. Defining the Management Server

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.

Note

If neither the ExecuteOnComputer nor the HostName parameter is present, the default value localhost will be assumed for both.

Id
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.
ExecuteOnComputer
This refers to the Id set for one of the computers defined in a [computer] section of the config.ini file.
PortNumber
This is the port number on which the management server listens for configuration requests and management commands.
HostName
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.
LogDestination
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.
  Note
  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_node_id_cluster.log,maxsize=1000000,maxfiles=6, where node_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
```
ArbitrationRank
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.
ArbitrationDelay
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.
DataDir
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.

19.3.4.5. Defining Data Nodes

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.

Id
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.
ExecuteOnComputer
This refers to the Id set for one of the computers defined in a [computer] section.
HostName
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.
ServerPort (OBSOLETE)
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.
NoOfReplicas
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 fail.
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. Currently, only the values 1 and 2 are actually supported (see Bug#18621).
Important
Setting NoOfReplicas to 1 means that there is only a single copy of all Cluster data; in this case, the loss of a single data node causes the cluster to fail because there are no additional copies of the data stored by that node.
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.
DataDir
This parameter specifies the directory where trace files, log files, pid files and error logs are placed.
FileSystemPath
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.
Note
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.
BackupDataDir
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:

DataMemory
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.
In addition, due to the way in which new pages are allocated when the capacity of the current page is exhausted, there is an additional overhead of approximately 18.75%. When more DataMemory is required, more than one new page is allocated, according to the following formula:
```
number of new pages = FLOOR(number of current pages × 0.1875) + 1
```
For example, if 15 pages are currently allocated to a given table and an insert to this table requires additional storage space, the number of new pages allocated to the table is FLOOR(15 × 0.1875) + 1 = FLOOR(2.8125) + 1 = 2 + 1 = 3. Now 15 + 3 = 18 memory pages are allocated to the table. When the last of these 18 pages becomes full, FLOOR(18 × 0.1875) + 1 = FLOOR(3.3750) + 1 = 3 + 1 = 4 new pages are allocated, so the total number of pages allocated to the table is now 22.
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.
IndexMemory
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.
StringMemory
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.

MaxNoOfConcurrentTransactions
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.
MaxNoOfConcurrentOperations
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.
MaxNoOfLocalOperations
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.
MaxNoOfFiredTriggers
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.
TransactionBufferMemory
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.

MaxNoOfConcurrentScans
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.
MaxNoOfLocalScans
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.
BatchSizePerLocalScan
This parameter is used to calculate the number of lock records used to handle concurrent scan operations.
The default value is 64; this value has a strong connection to the ScanBatchSize defined in the SQL nodes.
LongMessageBuffer
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.

NoOfFragmentLogFiles
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 19.3.6, “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 is always 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.
Important
This parameter cannot be changed “on the fly”; you must restart the node using --initial. If you wish to change this value for all data nodes in a running cluster, you can do so via a rolling node restart (using --initial when starting each data node).
MaxNoOfOpenFiles
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.
MaxNoOfSavedMessages
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.

MaxNoOfAttributes
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.
MaxNoOfTables
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.
MaxNoOfOrderedIndexes
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.
MaxNoOfUniqueHashIndexes
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.
MaxNoOfTriggers
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.
MaxNoOfIndexes
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.

LockPagesInMainMemory
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.
Important
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.
StopOnError
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.
Diskless
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.
Important
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.
RestartOnErrorInsert
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.

TimeBetweenWatchDogCheck
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).
StartPartialTimeout
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.
StartPartitionedTimeout
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).
StartFailureTimeout
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.
HeartbeatIntervalDbDb
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.
HeartbeatIntervalDbApi
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.
TimeBetweenLocalCheckpoints
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.
TimeBetweenGlobalCheckpoints
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).
TransactionInactiveTimeout
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 19.3.6, “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).
ArbitrationTimeout
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.

UndoIndexBuffer
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).
Important
It is not safe to decrease the value of this parameter during a rolling restart.
UndoDataBuffer
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).
Important
It is not safe to decrease the value of this parameter during a rolling restart.
RedoBuffer
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 in which 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).
Important
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.

LogLevelStartup
The reporting level for events generated during startup of the process.
The default level is 1.
LogLevelShutdown
The reporting level for events generated as part of graceful shutdown of a node.
The default level is 0.
LogLevelStatistic
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.
LogLevelCheckpoint
The reporting level for events generated by local and global checkpoints.
The default level is 0.
LogLevelNodeRestart
The reporting level for events generated during node restart.
The default level is 0.
LogLevelConnection
The reporting level for events generated by connections between cluster nodes.
The default level is 0.
LogLevelError
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.
LogLevelCongestion
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.
LogLevelInfo
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.

BackupDataBufferSize
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.
BackupLogBufferSize
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 19.9.4, “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.
BackupMemory
This parameter is simply the sum of BackupDataBufferSize and BackupLogBufferSize.
The default value is 2MB + 2MB = 4MB.
Important
If BackupDataBufferSize and BackupLogBufferSize taken together exceed 4MB, then this parameter must be set explicitly in the config.ini file to their sum.
BackupWriteSize
This parameter specifies the default size of messages written to disk by the backup log and backup data buffers.
The default value is 32KB.
BackupMaxWriteSize
This parameter specifies the maximum size of messages written to disk by the backup log and backup data buffers.
The default value is 256KB.

Important

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

19.3.4.6. Defining SQL and Other API Nodes

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.

Note

For a discussion of MySQL server options for MySQL Cluster, see Section 19.4.2, “MySQL Cluster-Related Command Options for mysqld”; for information about MySQL server system variables relating to MySQL Cluster, see Section 19.4.3, “MySQL Cluster System Variables”.

Id
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.
ExecuteOnComputer
This refers to the Id set for one of the computers (hosts) defined in a [computer] section of the configuration file.
HostName
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.
ArbitrationRank
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.
ArbitrationDelay
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.
BatchByteSize
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.
BatchSize
This parameter is measured in number of records and is by default set to 64. The maximum size is 992.
MaxScanBatchSize
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 5.1.6, “Status Variables”.

19.3.4.7. Cluster TCP/IP Connections

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 19.3.4.8, “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.

Important

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.

NodeId1, NodeId2
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 19.3.4.6, “Defining SQL and Other API Nodes”.
SendBufferMemory
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.
SendSignalId
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.
Checksum
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.
PortNumber (OBSOLETE)
This formerly specified the port number to be used for listening for connections from other nodes. This parameter should no longer be used.
ReceiveBufferMemory
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.

19.3.4.8. TCP/IP Connections Using Direct Connections

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 HostNameN parameter, where 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.

19.3.4.9. Shared-Memory Connections

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.

Important

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.

NodeId1, NodeId2
To identify a connection between two nodes it is necessary to provide node identifiers for each of them, as NodeId1 and NodeId2.
ShmKey
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.
ShmSize
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.
SendSignalId
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.
Checksum
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.

19.3.4.10. SCI Transport Connections

[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=/your/path/to/SCI. The path should point to a directory that contains at a minimum lib and include directories containing SISCI libraries and header files. (See Section 19.11, “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.

NodeId1, NodeId2
To identify a connection between two nodes it is necessary to provide node identifiers for each of them, as NodeId1 and NodeId2.
Host1SciId0
This identifies the SCI node ID on the first Cluster node (identified by NodeId1).
Host1SciId1
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.
Host2SciId0
This identifies the SCI node ID on the second Cluster node (identified by NodeId2).
Host2SciId1
When using two SCI cards to provide failover, this parameter identifies the second SCI card to be used on the second node.
SharedBufferSize
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.
SendLimit
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.
SendSignalId
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.
Checksum
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.

19.3.5. Overview of Cluster Configuration Parameters

19.3.5.1. Data Node Configuration Parameters
19.3.5.2. Management Node Configuration Parameters
19.3.5.3. SQL Node and API Node Configuration Parameters

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.

Important

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.)

19.3.5.1. Data Node Configuration Parameters

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 19.3.4.5, “Defining Data Nodes”.

Restart Type Column Values

N: Node Restart
IN: Initial Node Restart
S: System Restart
IS: Initial System Restart

See Section 19.3.5, “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	`FileSystemPath/BACKUP`	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	IN
`NoOfReplicas`	integer	None	1	4 (theoretical); 2 (supported)	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

19.3.5.2. Management Node Configuration Parameters

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 19.3.4.4, “Defining the Management Server”.

Restart Type Column Values

N: Node Restart
IN: Initial Node Restart
S: System Restart
IS: Initial System Restart

See Section 19.3.5, “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 19.3.4.4, “Defining the Management Server”)	N/A	N/A	N
`PortNumber`	integer	1186	1	65535	S

19.3.5.3. SQL Node and API Node Configuration Parameters

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 19.3.4.6, “Defining SQL and Other API Nodes”.

Note

Restart Type Column Values

N: Node Restart
IN: Initial Node Restart
S: System Restart
IS: Initial System Restart

See Section 19.3.5, “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

19.3.6. Configuring Parameters for Local Checkpoints

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.

19.4. MySQL Cluster Options and Variables

19.4.1. MySQL Cluster Server Option and Variable Reference
19.4.2. MySQL Cluster-Related Command Options for mysqld
19.4.3. MySQL Cluster System Variables
19.4.4. MySQL Cluster Status Variables

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 19.3, “MySQL Cluster Configuration”.

19.4.1. MySQL Cluster Server Option and Variable Reference

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
Handler_discover				Yes	Both	No
have_ndbcluster			Yes		Global	No
ndb_autoincrement_prefetch_sz	Yes	Yes	Yes		Both	Yes
ndb_cache_check_time	Yes	Yes	Yes		Global	Yes
ndbcluster	Yes	Yes	Yes		Both	Yes
Ndb_cluster_node_id				Yes	Both	No
Ndb_config_from_host				Yes	Both	No
Ndb_config_from_port				Yes	Both	No
ndb_force_send	Yes	Yes	Yes		Both	Yes
ndb_index_stat_cache_entries	Yes	Yes
ndb_index_stat_enable	Yes	Yes
ndb_index_stat_update_freq	Yes	Yes
ndb_optimized_node_selection	Yes	Yes
ndb_report_thresh_binlog_epoch_slip	Yes	Yes
ndb_report_thresh_binlog_mem_usage	Yes	Yes
ndb_use_exact_count			Yes		Both	Yes
ndb_use_transactions	Yes	Yes

19.4.2. MySQL Cluster-Related Command Options for mysqld

--ndb-connectstring=connect_string
When using the NDBCLUSTER storage engine, this option specifies the management server that distributes cluster configuration data. See Section 19.3.4.2, “The Cluster Connectstring”, for syntax.
--ndbcluster
The NDBCLUSTER storage engine is necessary for using MySQL Cluster. If a mysqld binary includes support for the NDBCLUSTER storage engine, the engine is disabled by default. Use the --ndbcluster option to enable it. Use --skip-ndbcluster to explicitly disable the engine.
--skip-ndbcluster
Disable the NDBCLUSTER storage engine. This is the default for binaries that were built with NDBCLUSTER storage engine support; the server allocates memory and other resources for this storage engine only if the --ndbcluster option is given explicitly. See Section 19.3.3, “Quick Test Setup of MySQL Cluster”, for an example of usage.

19.4.3. MySQL Cluster System Variables

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 5.1.5, “Using System Variables”.

have_ndbcluster
YES if mysqld supports NDBCLUSTER tables. DISABLED if --skip-ndbcluster is used.
multi_range_count
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
Type numeric
Default 256
Range 1-4294967295
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 is 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.

ndb_autoincrement_prefetch_sz

Option Sets Variable Yes, ndb_autoincrement_prefetch_sz

Variable Name ndb_autoincrement_prefetch_sz

Variable Scope Both

Dynamic Variable Yes

Value Set (<= 5.0.54)

Type	numeric
Default	`32`
Range	1-256

Value Set (>= 5.0.56)

Type	numeric
Default	`1`
Range	1-256

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)

ndb_cache_check_time
Option Sets Variable Yes, ndb_cache_check_time
Variable Name ndb_cache_check_time
Variable Scope Global
Dynamic Variable Yes
Value Set
Type numeric
Default 0
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.
ndb_force_send
Option Sets Variable Yes, ndb_force_send
Variable Name ndb_force_send
Variable Scope Both
Dynamic Variable Yes
Value Set
Type boolean
Default TRUE
Forces sending of buffers to NDB immediately, without waiting for other threads. Defaults to ON.
ndb_index_stat_cache_entries
Value Set
Type numeric
Default 32
Range 0-4294967295
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.
ndb_index_stat_enable
Value Set
Type boolean
Default ON
Use NDB index statistics in query optimization. Defaults to ON.
ndb_index_stat_update_freq
Value Set
Type numeric
Default 20
Range 0-4294967295
How often to query data nodes instead of the statistics cache. For example, a value of 20 (the default) means to direct every 20^th query to the data nodes.
ndb_optimized_node_selection
Value Set
Type boolean
Default ON
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
Type numeric
Default 3
Range 0-256
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
Type numeric
Default 10
Range 0-10
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.
ndb_use_exact_count
Variable Name ndb_use_exact_count
Variable Scope Both
Dynamic Variable Yes
Value Set
Type boolean
Default ON
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.
ndb_use_transactions
Value Set
Type boolean
Default ON
You can disable NDB transaction support by setting this variable's values to OFF (not recommended). The default is ON.

19.4.4. MySQL Cluster Status Variables

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 5.1.6, “Status Variables”.

Handler_discover
The MySQL server can ask the NDBCLUSTER 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.
Ndb_cluster_node_id
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.
Ndb_config_from_host
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.
Ndb_config_from_port
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.
Ndb_number_of_data_nodes
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.

19.5. Upgrading and Downgrading MySQL Cluster

19.5.1. Performing a Rolling Restart of the Cluster
19.5.2. MySQL Cluster 5.0 Upgrade and Downgrade Compatibility

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 19.5.2, “MySQL Cluster 5.0 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 19.3, “MySQL Cluster Configuration”.

This section remains in development, and continues to be updated and expanded.

19.5.1. Performing a Rolling Restart of the Cluster

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:

MySQL Cluster Rolling Restarts (By
Type)

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.

Important

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.

19.5.2. MySQL Cluster 5.0 Upgrade and Downgrade Compatibility

This section provides information about MySQL Cluster software and table file compatibility between MySQL 5.0 releases with regard to performing upgrades and downgrades.

Important

Only compatibility between MySQL versions with regard to NDBCLUSTER 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 releases of MySQL 5.0:

MySQL Cluster upgrade/downgrade compatibility,
MySQL 5.0

Notes.

MySQL 5.0.2 was the first public release in this series.
Direct upgrades or downgrades between MySQL Cluster 4.1 and 5.0 are not supported; you must dump all NDBCLUSTER tables using mysqldump, install the new version of the software, and then reload the tables from the dump.
Online downgrades from MySQL Cluster 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 of MySQL 5.0.23.

19.6. Process Management in MySQL Cluster

19.6.1. MySQL Server Process Usage for MySQL Cluster
19.6.2. ndbd — The Storage Engine Node Process
19.6.3. ndb_mgmd — The Management Server Process
19.6.4. ndb_mgm — The Management Client Process
19.6.5. Command Options for MySQL Cluster Processes

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:

19.6.1. MySQL Server Process Usage for MySQL Cluster

mysqld is the traditional MySQL server process. To be used with MySQL Cluster, mysqld needs to be built with support for the NDBCLUSTER 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 NDBCLUSTER 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 NDBCLUSTER 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 19.3.4.2, “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

Important

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.

19.6.2. ndbd — The Storage Engine Node Process

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_node_id_error.log 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:
```
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.
Important
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_node_id_trace.log.next file (see below). Error log entries are thus overwritten in a cyclical and not sequential fashion.
ndb_node_id_trace.log.trace_id 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.
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_node_id_trace.log.next is the file that keeps track of the next trace file number to be assigned.
ndb_node_id_out.log 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.
ndb_node_id.pid 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.
ndb_node_id_signal.log 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.

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 19.3.4.2, “The Cluster Connectstring”, for additional information about this issue. Section 19.6.5, “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 19.12, “Known Limitations of MySQL Cluster”.

19.6.3. ndb_mgmd — The Management Server Process

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 19.3.4.2, “The Cluster Connectstring”, for information about using connectstrings. Section 19.6.5, “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 19.3, “MySQL Cluster Configuration”, discusses how to set up this file.
ndb_node_id_cluster.log 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 19.7, “Management of MySQL Cluster”.
When the size of the cluster log reaches one million bytes, the file is renamed to ndb_node_id_cluster.log.seq_id, where 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_node_id_out.log is the file used for stdout and stderr when running the management server as a daemon.
ndb_node_id.pid is the process ID file used when running the management server as a daemon.

19.6.4. ndb_mgm — The Management Client Process

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 19.6.5.3, “Command Options for ndb_mgm”, and Section 19.7.2, “Commands in the MySQL Cluster Management Client”.

19.6.5. Command Options for MySQL Cluster Processes

19.6.5.1. Command Options for ndbd
19.6.5.2. Command Options for ndb_mgmd
19.6.5.3. Command Options for ndb_mgm

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 19.3.4.2, “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 4.2.3.1, “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 19.5.1, “Performing a Rolling Restart of the Cluster”).

The next few sections describe options specific to individual NDB programs.

See Section 19.4.2, “MySQL Cluster-Related Command Options for mysqld”, for mysqld options relating to MySQL Cluster.

19.6.5.1. Command Options for ndbd

For options common to all NDB programs, see Section 19.6.5, “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.
Important
This option does not affect any backup files that have already been created by the affected node.
Note
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 19.7.2, “Commands in the MySQL Cluster Management Client”).

19.6.5.2. Command Options for ndb_mgmd

For options common to NDB programs, see Section 19.6.5, “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.
Note
This option also can be given as -c file_name, but this shortcut is obsolete and should not be used in new installations.
--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.

19.6.5.3. Command Options for ndb_mgm

For options common to NDB programs, see Section 19.6.5, “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.

19.7. Management of MySQL Cluster

19.7.1. Summary of MySQL Cluster Start Phases
19.7.2. Commands in the MySQL Cluster Management Client
19.7.3. Event Reports Generated in MySQL Cluster
19.7.4. NDB Log Messages
19.7.5. Single User Mode
19.7.6. Quick Reference: MySQL Cluster SQL Statements

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 19.3, “MySQL Cluster Configuration”, and Section 19.6, “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 19.8, “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_node_id_cluster.log; this is usually found in the management server's DataDir directory, but this location can be overridden using the LogDestination option — see Section 19.3.4.4, “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 12.5.5.11, “SHOW ENGINE Syntax”, for more information.

19.7.1. Summary of MySQL Cluster Start Phases

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 node_id STATUS command in the management client. (See Section 19.7.2, “Commands in the MySQL Cluster Management Client”, for more information about this command.)

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.
Note
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.
Note
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.

19.7.2. Commands in the MySQL Cluster Management Client

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 19.7.3, “Event Reports Generated in MySQL Cluster”; commands for creating backups and restoring from backup are provided in Section 19.9, “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.
Note
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.
Note
ALL START continues to affect data nodes only.

Important
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.
Note
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.
Important
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.

19.7.3. Event Reports Generated in MySQL Cluster

19.7.3.1. Logging Management Commands
19.7.3.2. Log Events
19.7.3.3. Using CLUSTERLOG STATISTICS

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_node_id_cluster.log, (where node_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 19.3.4.4, “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_node_id_out.log (where node_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 YYYY-MM-DD HH:MM:SS format.
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.

19.7.3.1. Logging Management Commands

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 19.7.3.3, “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.

Note

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 `NDBCLUSTER` 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.

Important

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.

19.7.3.2. Log Events

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: Arbitration check failed — less than 1/2 nodes left Arbitration check succeeded — node group majority Arbitration check failed — missing node group Network partitioning — arbitration required Arbitration succeeded — affirmative response from node `X` Arbitration failed - negative response from node `X` Network partitioning - no arbitrator available Network partitioning - no arbitrator configured
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: Management server restarts arbitration thread [state=`X`] Prepare arbitrator node `X` [ticket=`Y`] Receive arbitrator node `X` [ticket=`Y`] Started arbitrator node `X` [ticket=`Y`] Lost arbitrator node `X` - process failure [state=`Y`] Lost arbitrator node `X` - process exit [state=`Y`] Lost arbitrator node `X` <error msg> [state=`Y`]

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`

19.7.3.3. Using `CLUSTERLOG STATISTICS`

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

Note

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.

19.7.4. `NDB` Log Messages

19.7.4.1. Messages in the Cluster Log
19.7.4.2. NDB Transporter Errors

This section contains information about the messages written to the cluster log in response to different cluster log events. It provides additional, more specific information on NDB transporter errors.

19.7.4.1. Messages in the Cluster Log

The following table lists the most common NDB cluster log messages. For information about the cluster log, log events, and event types, see Section 19.7.3, “Event Reports Generated in MySQL Cluster”. These log messages also correspond to log event types in the MGM API; see The Ndb_logevent_type Type, for related information of interest to Cluster API developers.

Log Message. Node mgm_node_id: Node data_node_id Connected

Description. The data node having node ID node_id has connected to the management server (node mgm_node_id).

Event Name. Connected

Event Type. Connection

Priority. 8

Severity. INFO

Log Message. Node mgm_node_id: Node data_node_id Disconnected

Description. The data node having node ID data_node_id has disconnected from the management server (node mgm_node_id).

Event Name. Disconnected

Event Type. Connection

Priority. 8

Severity. ALERT

Log Message. Node data_node_id: Communication to Node api_node_id closed

Description. The API node or SQL node having node ID api_node_id is no longer communicating with data node data_node_id.

Event Name. CommunicationClosed

Event Type. Connection

Priority. 8

Severity. INFO

Log Message. Node data_node_id: Communication to Node api_node_id opened

Description. The API node or SQL node having node ID api_node_id is now communicating with data node data_node_id.

Event Name. CommunicationOpened

Event Type. Connection

Priority. 8

Severity. INFO

Log Message. Node mgm_node_id: Node api_node_id: API version

Description. The API node having node ID api_node_id has connected to management node mgm_node_id using NDB API version version (generally the same as the MySQL version number).

Event Name. ConnectedApiVersion

Event Type. Connection

Priority. 8

Severity. INFO

Log Message. Node node_id: Global checkpoint gci started

Description. A global checkpoint with the ID gci has been started; node node_id is the master responsible for this global checkpoint.

Event Name. GlobalCheckpointStarted

Event Type. Checkpoint

Priority. 9

Severity. INFO

Log Message. Node node_id: Global checkpoint gci completed

Description. The global checkpoint having the ID gci has been completed; node node_id was the master responsible for this global checkpoint.

Event Name. GlobalCheckpointCompleted

Event Type. Checkpoint

Priority. 10

Severity. INFO

Log Message. Node node_id: Local checkpoint lcp started. Keep GCI = current_gci oldest restorable GCI = old_gci

Description. The local checkpoint having sequence ID lcp has been started on node node_id. The most recent GCI that can be used has the index current_gci, and the oldest GCI from which the cluster can be restored has the index old_gci.

Event Name. LocalCheckpointStarted

Event Type. Checkpoint

Priority. 7

Severity. INFO

Log Message. Node node_id: Local checkpoint lcp completed

Description. The local checkpoint having sequence ID lcp on node node_id has been completed.

Event Name. LocalCheckpointCompleted

Event Type. Checkpoint

Priority. 8

Severity. INFO

Log Message. Node node_id: Local Checkpoint stopped in CALCULATED_KEEP_GCI

Description. The node was unable to determine the most recent usable GCI.

Event Name. LCPStoppedInCalcKeepGci

Event Type. Checkpoint

Priority. 0

Severity. ALERT

Log Message. Node node_id: Table ID = table_id, fragment ID = fragment_id has completed LCP on Node node_id maxGciStarted: started_gci maxGciCompleted: completed_gci

Description. A table fragment has been checkpointed to disk on node node_id. The GCI in progress has the index started_gci, and the most recent GCI to have been completed has the index completed_gci.

Event Name. LCPFragmentCompleted

Event Type. Checkpoint

Priority. 11

Severity. INFO

Log Message. Node node_id: ACC Blocked num_1 and TUP Blocked num_2 times last second

Description. Undo logging is blocked because the log buffer is close to overflowing.

Event Name. UndoLogBlocked

Event Type. Checkpoint

Priority. 7

Severity. INFO

Log Message. Node node_id: Start initiated version

Description. Data node node_id, running NDB version version, is beginning its startup process.

Event Name. NDBStartStarted

Event Type. StartUp

Priority. 1

Severity. INFO

Log Message. Node node_id: Started version

Description. Data node node_id, running NDB version version, has started successfully.

Event Name. NDBStartCompleted

Event Type. StartUp

Priority. 1

Severity. INFO

Log Message. Node node_id: STTORRY received after restart finished

Description. The node has received a signal indicating that a cluster restart has completed.

Event Name. STTORRYRecieved

Event Type. StartUp

Priority. 15

Severity. INFO

Log Message. Node node_id: Start phase phase completed (type)

Description. The node has completed start phase phase of a type start. For a listing of start phases, see Section 19.7.1, “Summary of MySQL Cluster Start Phases”. (type is one of initial, system, node, initial node, or <Unknown>.)

Event Name. StartPhaseCompleted

Event Type. StartUp

Priority. 4

Severity. INFO

Log Message. Node node_id: CM_REGCONF president = president_id, own Node = own_id, our dynamic id = dynamic_id

Description. Node president_id has been selected as “president”. own_id and dynamic_id should always be the same as the ID (node_id) of the reporting node.

Event Name. CM_REGCONF

Event Type. StartUp

Priority. 3

Severity. INFO

Log Message. Node node_id: CM_REGREF from Node president_id to our Node node_id. Cause = cause

Description. The reporting node (ID node_id) was unable to accept node president_id as president. The cause of the problem is given as one of Busy, Election with wait = false, Not president, Election without selecting new candidate, or No such cause.

Event Name. CM_REGREF

Event Type. StartUp

Priority. 8

Severity. INFO

Log Message. Node node_id: We are Node own_id with dynamic ID dynamic_id, our left neighbour is Node id_1, our right is Node id_2

Description. The node has discovered its neighboring nodes in the cluster (node id_1 and node id_2). node_id, own_id, and dynamic_id should always be the same; if they are not, this indicates a serious misconfiguration of the cluster nodes.

Event Name. FIND_NEIGHBOURS

Event Type. StartUp

Priority. 8

Severity. INFO

Log Message. Node node_id: type shutdown initiated

Description. The node has received a shutdown signal. The type of shutdown is either Cluster or Node.

Event Name. NDBStopStarted

Event Type. StartUp

Priority. 1

Severity. INFO

Log Message. Node node_id: Node shutdown completed[, action] [Initiated by signal signal.]

Description. The node has been shut down. This report may include an action, which if present is one of restarting, no start, or initial. The report may also include a reference to an NDB Protocol signal; for possible signals, refer to Operations and Signals.

Event Name. NDBStopCompleted

Event Type. StartUp

Priority. 1

Severity. INFO

Log Message. Node node_id: Forced node shutdown completed[, action]. [Occured during startphase start_phase.] [Initiated by signal.] [Caused by error error_code: 'error_message(error_classification). error_status'. [(extra info extra_code)]]

Description. The node has been forcibly shut down. The action (one of restarting, no start, or initial) subsequently being taken, if any, is also reported. If the shutdown occurred while the node was starting, the report includes the start_phase during which the node failed. If this was a result of a signal sent to the node, this information is also provided (see Operations and Signals, for more information). If the error causing the failure is known, this is also included; for more information about NDB error messages and classifications, see NDB Errors.

Event Name. NDBStopForced

Event Type. StartUp

Priority. 1

Severity. ALERT

Log Message. Node node_id: Node shutdown aborted

Description. The node shutdown process was aborted by the user.

Event Name. NDBStopAborted

Event Type. StartUp

Priority. 1

Severity. INFO

Log Message. Node node_id: StartLog: [GCI Keep: keep_pos LastCompleted: last_pos NewestRestorable: restore_pos]

Description. This reports global checkpoints referenced during a node start. The redo log prior to keep_pos is dropped. last_pos is the last global checkpoint in which data node the participated; restore_pos is the global checkpoint which is actually used to restore all data nodes.

Event Name. StartREDOLog

Event Type. StartUp

Priority. 4

Severity. INFO

Log Message. startup_message [Listed separately; see below.]

Description. There are a number of possible startup messages that can be logged under different circumstances.

Event Name. StartReport

Event Type. StartUp

Priority. 4

Severity. INFO

Log Message. Node node_id: Node restart completed copy of dictionary information

Description. Copying of data dictionary information to the restarted node has been completed.

Event Name. NR_CopyDict

Event Type. NodeRestart

Priority. 8

Severity. INFO

Log Message. Node node_id: Node restart completed copy of distribution information

Description. Copying of data distribution information to the restarted node has been completed.

Event Name. NR_CopyDistr

Event Type. NodeRestart

Priority. 8

Severity. INFO

Log Message. Node node_id: Node restart starting to copy the fragments to Node node_id

Description. Copy of fragments to starting data node node_id has begun

Event Name. NR_CopyFragsStarted

Event Type. NodeRestart

Priority. 8

Severity. INFO

Log Message. Node node_id: Table ID = table_id, fragment ID = fragment_id have been copied to Node node_id

Description. Fragment fragment_id from table table_id has been copied to data node node_id

Event Name. NR_CopyFragDone

Event Type. NodeRestart

Priority. 10

Severity. INFO

Log Message. Node node_id: Node restart completed copying the fragments to Node node_id

Description. Copying of all table fragments to restarting data node node_id has been completed

Event Name. NR_CopyFragsCompleted

Event Type. NodeRestart

Priority. 8

Severity. INFO

Log Message. Any of the following:

Node node_id: Node node1_id completed failure of Node node2_id
All nodes completed failure of Node node_id
Node failure of node_idblock completed

Description. One of the following (each corresponding to the same-numbered message listed above):

Data node node1_id has detected the failure of data node node2_id
All (remaining) data nodes have detected the failure of data node node_id
The failure of data node node_id has been detected in the blockNDB kernel block, where block is 1 of DBTC, DBDICT, DBDIH, or DBLQH; for more information, see NDB Kernel Blocks

Event Name. NodeFailCompleted

Event Type. NodeRestart

Priority. 8

Severity. ALERT

Log Message. Node mgm_node_id: Node data_node_id has failed. The Node state at failure was state_code

Description. A data node has failed. Its state at the time of failure is described by an arbitration state code state_code: possible state code values can be found in the file include/kernel/signaldata/ArbitSignalData.hpp.

Event Name. NODE_FAILREP

Event Type. NodeRestart

Priority. 8

Severity. ALERT

Log Message. President restarts arbitration thread [state=state_code] or Prepare arbitrator node node_id [ticket=ticket_id] or Receive arbitrator node node_id [ticket=ticket_id] or Started arbitrator node node_id [ticket=ticket_id] or Lost arbitrator node node_id - process failure [state=state_code] or Lost arbitrator node node_id - process exit [state=state_code] or Lost arbitrator node node_id - error_message [state=state_code]

Description. This is a report on the current state and progress of arbitration in the cluster. node_id is the node ID of the management node or SQL node selected as the arbitrator. state_code is an arbitration state code, as found in include/kernel/signaldata/ArbitSignalData.hpp. When an error has occurred, an error_message, also defined in ArbitSignalData.hpp, is provided. ticket_id is a unique identifier handed out by the arbitrator when it is selected to all the nodes that participated in its selection; this is used to insure that each node requesting arbitration was one of the nodes that took part in the selection process.

Event Name. ArbitState

Event Type. NodeRestart

Priority. 6

Severity. INFO

Log Message. Arbitration check lost - less than 1/2 nodes left or Arbitration check won - all node groups and more than 1/2 nodes left or Arbitration check won - node group majority or Arbitration check lost - missing node group or Network partitioning - arbitration required or Arbitration won - positive reply from node node_id or Arbitration lost - negative reply from node node_id or Network partitioning - no arbitrator available or Network partitioning - no arbitrator configured or Arbitration failure - error_message [state=state_code]

Description. This message reports on the result of arbitration. In the event of arbitration failure, an error_message and an arbitration state_code are provided; definitions for both of these are found in include/kernel/signaldata/ArbitSignalData.hpp.

Event Name. ArbitResult

Event Type. NodeRestart

Priority. 2

Severity. ALERT

Log Message. Node node_id: GCP Take over started

Description. This node is attempting to assume responsibility for the next global checkpoint (that is, it is becoming the master node)

Event Name. GCP_TakeoverStarted

Event Type. NodeRestart

Priority. 7

Severity. INFO

Log Message. Node node_id: GCP Take over completed

Description. This node has become the master, and has assumed responsibility for the next global checkpoint

Event Name. GCP_TakeoverCompleted

Event Type. NodeRestart

Priority. 7

Severity. INFO

Log Message. Node node_id: LCP Take over started

Description. This node is attempting to assume responsibility for the next set of local checkpoints (that is, it is becoming the master node)

Event Name. LCP_TakeoverStarted

Event Type. NodeRestart

Priority. 7

Severity. INFO

Log Message. Node node_id: LCP Take over completed

Description. This node has become the master, and has assumed responsibility for the next set of local checkpoints

Event Name. LCP_TakeoverCompleted

Event Type. NodeRestart

Priority. 7

Severity. INFO

Log Message. Node node_id: Trans. Count = transactions, Commit Count = commits, Read Count = reads, Simple Read Count = simple_reads, Write Count = writes, AttrInfo Count = AttrInfo_objects, Concurrent Operations = concurrent_operations, Abort Count = aborts, Scans = scans, Range scans = range_scans

Description. This report of transaction activity is given approximately once every 10 seconds

Event Name. TransReportCounters

Event Type. Statistic

Priority. 8

Severity. INFO

Log Message. Node node_id: Operations=operations

Description. Number of operations performed by this node, provided approximately once every 10 seconds

Event Name. OperationReportCounters

Event Type. Statistic

Priority. 8

Severity. INFO

Log Message. Node node_id: Table with ID = table_id created

Description. A table having the table ID shown has been created

Event Name. TableCreated

Event Type. Statistic

Priority. 7

Severity. INFO

Log Message. Node node_id: Mean loop Counter in doJob last 8192 times = count

Description.

Event Name. JobStatistic

Event Type. Statistic

Priority. 9

Severity. INFO

Log Message. Mean send size to Node = node_id last 4096 sends = bytes bytes

Description. This node is sending an average of bytes bytes per send to node node_id

Event Name. SendBytesStatistic

Event Type. Statistic

Priority. 9

Severity. INFO

Log Message. Mean receive size to Node = node_id last 4096 sends = bytes bytes

Description. This node is receiving an average of bytes of data each time it receives data from node node_id

Event Name. ReceiveBytesStatistic

Event Type. Statistic

Priority. 9

Severity. INFO

Log Message. Node node_id: Data usage is data_memory_percentage% (data_pages_used 32K pages of total data_pages_total) / Node node_id: Index usage is index_memory_percentage% (index_pages_used 8K pages of total index_pages_total)

Description. This report is generated when a DUMP 1000 command is issued in the cluster management client; for more information, see DUMP 1000, in MySQL Cluster Internals

Event Name. MemoryUsage

Event Type. Statistic

Priority. 5

Severity. INFO

Log Message. Node node1_id: Transporter to node node2_id reported error error_code: error_message

Description. A transporter error occurred while communicating with node node2_id; for a listing of transporter error codes and messages, see NDB Transporter Errors, in MySQL Cluster Internals

Event Name. TransporterError

Event Type. Error

Priority. 2

Severity. ERROR

Log Message. Node node1_id: Transporter to node node2_id reported error error_code: error_message

Description. A warning of a potential transporter problem while communicating with node node2_id; for a listing of transporter error codes and messages, see NDB Transporter Errors, for more information

Event Name. TransporterWarning

Event Type. Error

Priority. 8

Severity. WARNING

Log Message. Node node1_id: Node node2_id missed heartbeat heartbeat_id

Description. This node missed a heartbeat from node node2_id

Event Name. MissedHeartbeat

Event Type. Error

Priority. 8

Severity. WARNING

Log Message. Node node1_id: Node node2_id declared dead due to missed heartbeat

Description. This node has missed at least 3 heartbeats from node node2_id, and so has declared that node “dead”

Event Name. DeadDueToHeartbeat

Event Type. Error

Priority. 8

Severity. ALERT

Log Message. Node node1_id: Node Sent Heartbeat to node = node2_id

Description. This node has sent a heartbeat to node node2_id

Event Name. SentHeartbeat

Event Type. Info

Priority. 12

Severity. INFO

Log Message. Node node_id: Event buffer status: used=bytes_used (percent_used%) alloc=bytes_allocated (percent_available%) max=bytes_available apply_gci=latest_restorable_GCI latest_gci=latest_GCI

Description. This report is seen during heavy event buffer usage, for example, when many updates are being applied in a relatively short period of time; the report shows the number of bytes and the percentage of event buffer memory used, the bytes allocated and percentage still available, and the latest and latest restorable global checkpoints

Event Name. EventBufferStatus

Event Type. Info

Priority. 7

Severity. INFO

Log Message. Node node_id: Entering single user mode, Node node_id: Entered single user mode Node API_node_id has exclusive access, Node node_id: Entering single user mode

Description. These reports are written to the cluster log when entering and exiting single user mode; API_node_id is the node ID of the API or SQL having exclusive access to the cluster (fro mroe information, see Section 19.7.5, “Single User Mode”); the message Unknown single user report API_node_id indicates an error has taken place and should never be seen in normal operation

Event Name. SingleUser

Event Type. Info

Priority. 7

Severity. INFO

Log Message. Node node_id: Backup backup_id started from node mgm_node_id

Description. A backup has been started using the management node having mgm_node_id; this message is also displayed in the cluster management client when the START BACKUP command is issued; for more information, see Section 19.9.2, “Using The Management Client to Create a Backup”

Event Name. BackupStarted

Event Type. Backup

Priority. 7

Severity. INFO

Log Message. Node node_id: Backup backup_id started from node mgm_node_id completed. StartGCP: start_gcp StopGCP: stop_gcp #Records: records #LogRecords: log_records Data: data_bytes bytes Log: log_bytes bytes

Description. The backup having the ID backup_id has been completed; for more information, see Section 19.9.2, “Using The Management Client to Create a Backup”

Event Name. BackupCompleted

Event Type. Backup

Priority. 7

Severity. INFO

Log Message. Node node_id: Backup request from mgm_node_id failed to start. Error: error_code

Description. The backup failed to start; for error codes, see MGM API Errors

Event Name. BackupFailedToStart

Event Type. Backup

Priority. 7

Severity. ALERT

Log Message. Node node_id: Backup backup_id started from mgm_node_id has been aborted. Error: error_code

Description. The backup was terminated after starting, possibly due to user intervention

Event Name. BackupAborted

Event Type. Backup

Priority. 7

Severity. ALERT

19.7.4.2. `NDB` Transporter Errors

This section lists error codes, names, and messages that are written to the cluster log in the event of transporter errors.

Error Code	Error Name	Error Text
0x00	TE_NO_ERROR	No error
0x01	TE_ERROR_CLOSING_SOCKET	Error found during closing of socket
0x02	TE_ERROR_IN_SELECT_BEFORE_ACCEPT	Error found before accept. The transporter will retry
0x03	TE_INVALID_MESSAGE_LENGTH	Error found in message (invalid message length)
0x04	TE_INVALID_CHECKSUM	Error found in message (checksum)
0x05	TE_COULD_NOT_CREATE_SOCKET	Error found while creating socket(can't create socket)
0x06	TE_COULD_NOT_BIND_SOCKET	Error found while binding server socket
0x07	TE_LISTEN_FAILED	Error found while listening to server socket
0x08	TE_ACCEPT_RETURN_ERROR	Error found during accept(accept return error)
0x0b

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