Replication in MySQL Cluster makes use of a number of dedicated tables in the mysql database on each MySQL Server instance acting as an SQL node in both the cluster being replicated and the replication slave (whether the slave is a single server or a cluster). These tables are created during the MySQL installation process by the mysql_install_db script, and include a table for storing the binary log's indexing data. Since the ndb_binlog_index table is local to each MySQL server and does not participate in clustering, it uses the MyISAM storage engine. This means that it must be created separately on each mysqld participating in the master cluster. (However, the binlog itself contains updates from all MySQL servers in the cluster to be replicated.) This table is defined as follows:

        
CREATE TABLE `ndb_binlog_index` (
          `Position`  BIGINT(20) UNSIGNED NOT NULL,
          `File`      VARCHAR(255) NOT NULL,
          `epoch`     BIGINT(20) UNSIGNED NOT NULL,
          `inserts`   BIGINT(20) UNSIGNED NOT NULL,
          `updates`   BIGINT(20) UNSIGNED NOT NULL,
          `deletes`   BIGINT(20) UNSIGNED NOT NULL,
          `schemaops` BIGNINT(20) UNSIGNED NOT NULL,
          PRIMARY KEY (`epoch`)
) ENGINE=MYISAM  DEFAULT CHARSET=latin1;

Important: Prior to MySQL 5.1.14, the ndb_binlog_index table was known as binlog_index, and was kept in a separate cluster database, which in MySQL 5.1.7 and earlier was known as the cluster_replication database. Similarly, the ndb_apply_status and ndb_schema tables were known as apply_status and schema, and were also found in the cluster (earlier cluster_replication) database. However, beginning with MySQL 5.1.14, all MySQL Cluster replication tables reside in the mysql system database.

Information about how this change affects upgrades from MySQL Cluster 5.1.13 and earlier to 5.1.14 and later versions can be found in Section C.1.5, “Changes in release 5.1.14 (05 December 2006)”.

The following figure shows the relationship of the MySQL Cluster replication master server, its binlog injector thread, and the mysql.ndb_binlog_index table.

An additional table, named ndb_apply_status, is used to keep a record of the operations that have been replicated from the master to the slave. Unlike the case with ndb_binlog_index, the data in this table is not specific to any one SQL node in the (slave) cluster, and so ndb_apply_status can use the NDB Cluster storage engine, as shown here:

CREATE TABLE `ndb_apply_status` (
    `server_id` INT(10) UNSIGNED NOT NULL,
    `epoch`     BIGINT(20) UNSIGNED NOT NULL,
    PRIMARY KEY  USING HASH (`server_id`)
) ENGINE=NDBCLUSTER  DEFAULT CHARSET=latin1;

The ndb_binlog_index and ndb_apply_status tables are created in the mysql database because they should not be replicated. No user intervention is normally required to create or maintain either of them. Both the ndb_binlog_index and the ndb_apply_status tables are maintained by the NDB injector thread. This keeps the master mysqld process updated to changes performed by the NDB storage engine. The NDB binlog injector thread receives events directly from the NDB storage engine. The NDB injector is responsible for capturing all the data events within the cluster, and ensures that all events which change, insert, or delete data are recorded in the ndb_binlog_index table. The slave I/O thread transfers the events from the master's binary log to the slave's relay log.

However, it is advisable to check for the existence and integrity of these tables as an initial step in preparing a MySQL Cluster for replication. It is possible to view event data recorded in the binary log by querying the mysql.binlog_index table directly on the master. This can be also be accomplished using the SHOW BINLOG EVENTS statement on either the replication master or slave MySQL servers. (See Section 13.6.1.4, “SHOW BINLOG EVENTS Syntax”.)

You can also obtain useful information from the output of SHOW ENGINE NDB STATUS.

Note: Beginning with MySQL 5.1.14, if the apply_status table does not exist on the slave, it is created by ndb_restore. (Bug#14612)