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17.5.9 Quick Reference: MySQL Cluster SQL Statements

This section discusses several SQL statements that can prove useful in managing and monitoring a MySQL server that is connected to a MySQL Cluster, and in some cases provide information about the cluster itself.

  • SHOW ENGINE NDB STATUS, SHOW ENGINE NDBCLUSTER STATUS

    The output of this statement contains information about the server's connection to the cluster, creation and usage of MySQL Cluster objects, and binary logging for MySQL Cluster replication.

    See Section 13.7.5.16, “SHOW ENGINE Syntax”, for a usage example and more detailed information.

  • SHOW ENGINES

    This statement can be used to determine whether or not clustering support is enabled in the MySQL server, and if so, whether it is active.

    See Section 13.7.5.17, “SHOW ENGINES Syntax”, for more detailed information.

    Note

    In MySQL 5.1 and later, this statement does not support a LIKE clause. However, you can use LIKE to filter queries against the INFORMATION_SCHEMA.ENGINES table, as discussed in the next item.

  • SELECT * FROM INFORMATION_SCHEMA.ENGINES [WHERE ENGINE LIKE 'NDB%']

    This is the equivalent of SHOW ENGINES, but uses the ENGINES table of the INFORMATION_SCHEMA database (available beginning with MySQL 5.1.5). Unlike the case with the SHOW ENGINES statement, it is possible to filter the results using a LIKE clause, and to select specific columns to obtain information that may be of use in scripts. For example, the following query shows whether the server was built with NDB support and, if so, whether it is enabled:

    mysql> SELECT SUPPORT FROM INFORMATION_SCHEMA.ENGINES
        ->   WHERE ENGINE LIKE 'NDB%';
    +---------+
    | support |
    +---------+
    | ENABLED |
    +---------+
    

    See Section 20.6, “The INFORMATION_SCHEMA ENGINES Table”, for more information.

  • SHOW VARIABLES LIKE 'NDB%'

    This statement provides a list of most server system variables relating to the NDB storage engine, and their values, as shown here:

    mysql> SHOW VARIABLES LIKE 'NDB%';
    +-------------------------------------+-------+
    | Variable_name                       | Value |
    +-------------------------------------+-------+
    | ndb_autoincrement_prefetch_sz       | 32    |
    | ndb_cache_check_time                | 0     |
    | ndb_extra_logging                   | 0     |
    | ndb_force_send                      | ON    |
    | ndb_index_stat_cache_entries        | 32    |
    | ndb_index_stat_enable               | OFF   |
    | ndb_index_stat_update_freq          | 20    |
    | ndb_report_thresh_binlog_epoch_slip | 3     |
    | ndb_report_thresh_binlog_mem_usage  | 10    |
    | ndb_use_copying_alter_table         | OFF   |
    | ndb_use_exact_count                 | ON    |
    | ndb_use_transactions                | ON    |
    +-------------------------------------+-------+
    

    See Section 5.1.4, “Server System Variables”, for more information.

  • SELECT * FROM INFORMATION_SCHEMA.GLOBAL_VARIABLES WHERE VARIABLE_NAME LIKE 'NDB%';

    This statement is the equivalent of the SHOW command described in the previous item, and provides almost identical output, as shown here:

    mysql> SELECT * FROM INFORMATION_SCHEMA.GLOBAL_VARIABLES
        ->   WHERE VARIABLE_NAME LIKE 'NDB%';
    +-------------------------------------+----------------+
    | VARIABLE_NAME                       | VARIABLE_VALUE |
    +-------------------------------------+----------------+
    | NDB_AUTOINCREMENT_PREFETCH_SZ       | 32             |
    | NDB_CACHE_CHECK_TIME                | 0              |
    | NDB_EXTRA_LOGGING                   | 0              |
    | NDB_FORCE_SEND                      | ON             |
    | NDB_INDEX_STAT_CACHE_ENTRIES        | 32             |
    | NDB_INDEX_STAT_ENABLE               | OFF            |
    | NDB_INDEX_STAT_UPDATE_FREQ          | 20             |
    | NDB_REPORT_THRESH_BINLOG_EPOCH_SLIP | 3              |
    | NDB_REPORT_THRESH_BINLOG_MEM_USAGE  | 10             |
    | NDB_USE_COPYING_ALTER_TABLE         | OFF            |
    | NDB_USE_EXACT_COUNT                 | ON             |
    | NDB_USE_TRANSACTIONS                | ON             |
    +-------------------------------------+----------------+
    

    Unlike the case with the SHOW command, it is possible to select individual columns. For example:

    mysql> SELECT VARIABLE_VALUE 
        ->   FROM INFORMATION_SCHEMA.GLOBAL_VARIABLES
        ->   WHERE VARIABLE_NAME = 'ndb_force_send';
    +----------------+
    | VARIABLE_VALUE |
    +----------------+
    | ON             |
    +----------------+
    

    See Section 20.9, “The INFORMATION_SCHEMA GLOBAL_VARIABLES and SESSION_VARIABLES Tables”, and Section 5.1.4, “Server System Variables”, for more information.

  • SHOW STATUS LIKE 'NDB%'

    This statement shows at a glance whether or not the MySQL server is acting as a cluster SQL node, and if so, it provides the MySQL server's cluster node ID, the host name and port for the cluster management server to which it is connected, and the number of data nodes in the cluster, as shown here:

    mysql> SHOW STATUS LIKE 'NDB%';
    +--------------------------+---------------+
    | Variable_name            | Value         |
    +--------------------------+---------------+
    | Ndb_cluster_node_id      | 10            |
    | Ndb_config_from_host     | 192.168.0.103 |
    | Ndb_config_from_port     | 1186          |
    | Ndb_number_of_data_nodes | 4             |
    +--------------------------+---------------+
    

    If the MySQL server was built with clustering support, but it is not connected to a cluster, all rows in the output of this statement contain a zero or an empty string:

    mysql> SHOW STATUS LIKE 'NDB%';
    +--------------------------+-------+
    | Variable_name            | Value |
    +--------------------------+-------+
    | Ndb_cluster_node_id      | 0     |
    | Ndb_config_from_host     |       |
    | Ndb_config_from_port     | 0     |
    | Ndb_number_of_data_nodes | 0     |
    +--------------------------+-------+
    

    See also Section 13.7.5.37, “SHOW STATUS Syntax”.

  • SELECT * FROM INFORMATION_SCHEMA.GLOBAL_STATUS WHERE VARIABLE_NAME LIKE 'NDB%';

    Beginning with MySQL 5.1.12, this statement provides similar output to the SHOW command discussed in the previous item. However, unlike the case with SHOW STATUS, it is possible using the SELECT to extract values in SQL for use in scripts for monitoring and automation purposes.

    See Section 20.8, “The INFORMATION_SCHEMA GLOBAL_STATUS and SESSION_STATUS Tables”, for more information.

Beginning with MySQL Cluster NDB 7.1.1, you can also query the tables in the ndbinfo information database for real-time data about many MySQL Cluster operations. See Section 17.5.10, “The ndbinfo MySQL Cluster Information Database”.


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