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15.4.4.6. 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.

  • 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 other than localhost, either this parameter or ExecuteOnComputer is required.

  • 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 5.2.5, “Status Variables”.