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15.4.4 MySQL Cluster Status Variables »
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15.4.3. 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”.

  • ndb_autoincrement_prefetch_sz

    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.

  • ndb_cache_check_time

    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

    Forces sending of buffers to NDB immediately, without waiting for other threads. Defaults to ON.

  • ndb_index_stat_cache_entries

    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

    Use NDB index statistics in query optimization. Defaults to ON.

  • ndb_index_stat_update_freq

    How often to query data nodes instead of the statistics cache. For example, a value of 20 (the default) means to direct every 20th query to the data nodes.

  • ndb_optimized_node_selection

    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.

    Added in MySQL 4.1.9.

  • ndb_report_thresh_binlog_epoch_slip

    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

    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

    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

    You can disable NDB transaction support by setting this variable's values to OFF (not recommended). The default is ON.