25.6.10 MySQL Server Usage for NDB Cluster

mysqld is the traditional MySQL server process. To be used with NDB Cluster, mysqld needs to be built with support for the NDB storage engine, as it is in the precompiled binaries available from https://dev.mysql.com/downloads/. If you build MySQL from source, you must invoke CMake with the -DWITH_NDB=1 or (deprecated) -DWITH_NDBCLUSTER=1 option to include support for NDB.

For more information about compiling NDB Cluster from source, see Section 25.3.1.4, “Building NDB Cluster from Source on Linux”, and Section 25.3.2.2, “Compiling and Installing NDB Cluster from Source on Windows”.

(For information about mysqld options and variables, in addition to those discussed in this section, which are relevant to NDB Cluster, see Section 25.4.3.9, “MySQL Server Options and Variables for NDB Cluster”.)

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 host name or IP address for the management server

• 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 connection string either on the command line when starting mysqld or in my.cnf. The connection string contains the host name 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:

$> mysqld --ndbcluster --ndb-connectstring=ndb_mgmd.mysql.com:1186

See Section 25.4.3.3, “NDB Cluster Connection Strings”, for more information on connection strings.

Given this information, the MySQL server can act as a full participant in the cluster. (We often refer to a mysqld process running in this manner as an SQL node.) It is fully aware of all cluster data nodes as well as their status, and establishes 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 an NDB 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 an NDB Cluster, you must restart the server without the --ndbcluster option.