5.3.7 Defining SQL and Other API Nodes in an NDB Cluster

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 synonymous; you can, for instance, list parameters for a MySQL server acting as an SQL node in an [api] section.

Note

For a discussion of MySQL server options for NDB Cluster, see Section 5.3.8.1, “MySQL Server Options for NDB Cluster”. For information about MySQL server system variables relating to NDB Cluster, see Section 5.3.8.2, “NDB Cluster System Variables”.

• Id

  The Id is an integer value used to identify the node in all cluster internal messages. The permitted range of values is 1 to 255 inclusive. This value must be unique for each node in the cluster, regardless of the type of node.

  Note

  Data node IDs must be less than 49, regardless of the NDB Cluster version used. If you plan to deploy a large number of data nodes, it is a good idea to limit the node IDs for API nodes (and management nodes) to values greater than 48.

  NodeId is the preferred parameter name to use when identifying API nodes. (Id continues to be supported for backward compatibility, but is now deprecated and generates a warning when used. It is also subject to future removal.)

• ConnectionMap

  Specifies which data nodes to connect.

• NodeId

  The NodeId is an integer value used to identify the node in all cluster internal messages. The permitted range of values is 1 to 255 inclusive. This value must be unique for each node in the cluster, regardless of the type of node.

  Note

  Data node IDs must be less than 49, regardless of the NDB Cluster version used. If you plan to deploy a large number of data nodes, it is a good idea to limit the node IDs for API nodes (and management nodes) to values greater than 48.

  NodeId is the preferred parameter name to use when identifying management nodes. An alias, Id, was used for this purpose in very old versions of NDB Cluster, and continues to be supported for backward compatibility; it is now deprecated and generates a warning when used, and is subject to removal in a future release of NDB 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, either this parameter or ExecuteOnComputer is required.

  If no HostName or ExecuteOnComputer is specified in a given [mysql] or [api] section of the config.ini file, then an SQL or API node may connect using the corresponding “slot” from any host which can establish a network connection to the management server host machine. This differs from the default behavior for data nodes, where localhost is assumed for HostName unless otherwise specified.

• ArbitrationRank

  This parameter defines which nodes can act as arbitrators. Both management 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 for management nodes) and those for all SQL nodes to 0 (the default for SQL nodes).

  By setting ArbitrationRank to 0 on all management and SQL nodes, you can disable arbitration completely. You can also control arbitration by overriding this parameter; to do so, set the Arbitration parameter in the [ndbd default] section of the config.ini global configuration file.

• ArbitrationDelay

  Setting this parameter to any other value than 0 (the default) means that responses by the arbitrator to arbitration requests are 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.

  This parameter is measured in bytes. The default value in NDB Cluster 7.3 and later is 16K.

• BatchSize

  This parameter is measured in number of records and is by default set to 256. The maximum size is 992.

• ExtraSendBufferMemory

  This parameter specifies the amount of transporter send buffer memory to allocate in addition to any that has been set using TotalSendBufferMemory, SendBufferMemory, or both.

• HeartbeatThreadPriority

  Use this parameter to set the scheduling policy and priority of heartbeat threads for management and API nodes. The syntax for setting this parameter is shown here:

  HeartbeatThreadPriority = policy[, priority]
  policy:
    {FIFO | RR}

  When setting this parameter, you must specify a policy. This is one of FIFO (first in, first in) or RR (round robin). This followed optionally by the priority (an integer).

• 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.

• TotalSendBufferMemory

  This parameter is used to determine the total amount of memory to allocate on this node for shared send buffer memory among all configured transporters.

  If this parameter is set, its minimum permitted value is 256KB; 0 indicates that the parameter has not been set. For more detailed information, see Section 5.3.12, “Configuring NDB Cluster Send Buffer Parameters”.

• AutoReconnect

  This parameter is false by default. This forces disconnected API nodes (including MySQL Servers acting as SQL nodes) to use a new connection to the cluster rather than attempting to re-use an existing one, as re-use of connections can cause problems when using dynamically-allocated node IDs. (Bug #45921)

  Note

  This parameter can be overridden using the NDB API. For more information, see Ndb_cluster_connection::set_auto_reconnect(), and Ndb_cluster_connection::get_auto_reconnect().

• DefaultOperationRedoProblemAction

  This parameter (along with RedoOverCommitLimit and RedoOverCommitCounter) controls the data node's handling of operations when too much time is taken flushing redo logs to disk. This occurs when a given redo log flush takes longer than RedoOverCommitLimit seconds, more than RedoOverCommitCounter times, causing any pending transactions to be aborted.

  When this happens, the node can respond in either of two ways, according to the value of DefaultOperationRedoProblemAction, listed here:

  • ABORT: Any pending operations from aborted transactions are also aborted.

  • QUEUE: Pending operations from transactions that were aborted are queued up to be re-tried. This the default. In NDB 7.3.10 and later as well as NDB 7.4.7 and later, pending operations are still aborted when the redo log runs out of space—that is, when P_TAIL_PROBLEM errors occur. (Bug #20782580)

• DefaultHashMapSize

  The size of the table hash maps used by NDB is configurable using this parameter. DefaultHashMapSize can take any of three possible values (0, 240, 3840).

  The original intended use for this parameter was to facilitate upgrades and especially downgrades to and from very old releases with differing default hash map sizes. This is not an issue when upgrading from NDB Cluster 7.3 (or later) to later versions.

  Decreasing this parameter online after any tables have been created or modified with DefaultHashMapSize equal to 3840 is not currently supported.

• Wan

  Use WAN TCP setting as default.

• ConnectBackoffMaxTime

  Starting with NDB 7.3.7 and NDB 7.4.2, in an NDB Cluster with many unstarted data nodes, the value of this parameter can be raised to circumvent connection attempts to data nodes which have not yet begun to function in the cluster, as well as moderate high traffic to management nodes. As long as the API node is not connected to any new data nodes, the value of the StartConnectBackoffMaxTime parameter is applied; otherwise, ConnectBackoffMaxTime is used to determine the length of time in milliseconds to wait between connection attempts.

  Time elapsed during node connection attempts is not taken into account when calculating elapsed time for this parameter. The timeout is applied with approximately 100 ms resolution, starting with a 100 ms delay; for each subsequent attempt, the length of this period is doubled until it reaches ConnectBackoffMaxTime milliseconds, up to a maximum of 100000 ms (100s).

  Once the API node is connected to a data node and that node reports (in a heartbeat message) that it has connected to other data nodes, connection attempts to those data nodes are no longer affected by this parameter, and are made every 100 ms thereafter until connected. Once a data node has started, it can take up HeartbeatIntervalDbApi for the API node to be notified that this has occurred.

• StartConnectBackoffMaxTime

  Starting with NDB 7.3.7 and NDB 7.4.2, in an NDB Cluster with many unstarted data nodes, the value of this parameter can be raised to circumvent connection attempts to data nodes which have not yet begun to function in the cluster, as well as moderate high traffic to management nodes. As long as the API node is not connected to any new data nodes, the value of the StartConnectBackoffMaxTime parameter is applied; otherwise, ConnectBackoffMaxTime is used to determine the length of time in milliseconds to wait between connection attempts.

  Time elapsed during node connection attempts is not taken into account when calculating elapsed time for this parameter. The timeout is applied with approximately 100 ms resolution, starting with a 100 ms delay; for each subsequent attempt, the length of this period is doubled until it reaches StartConnectBackoffMaxTime milliseconds, up to a maximum of 100000 ms (100s).

  Once the API node is connected to a data node and that node reports (in a heartbeat message) that it has connected to other data nodes, connection attempts to those data nodes are no longer affected by this parameter, and are made every 100 ms thereafter until connected. Once a data node has started, it can take up HeartbeatIntervalDbApi for the API node to be notified that this has occurred.

API Node Debugging Parameters.  Beginning with NDB 7.4.12, you can use the ApiVerbose configuration parameter to enable debugging output from a given API node. This parameter takes an integer value. 0 is the default, and disables such debugging; 1 enables debugging output to the cluster log; 2 adds DBDICT debugging output as well. (Bug #20638450) See also DUMP 1229.

You can also obtain information from a MySQL server running as an NDB 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        | 198.51.100.112 |
| Ndb_config_from_port        | 1186           |
| Ndb_number_of_storage_nodes | 4              |
+-----------------------------+----------------+
4 rows in set (0.02 sec)

For information about the status variables appearing in the output from this statement, see Section 5.3.8.3, “NDB Cluster Status Variables”.

Note

To add new SQL or API nodes to the configuration of a running NDB Cluster, it is necessary to perform a rolling restart of all cluster nodes after adding new [mysqld] or [api] sections to the config.ini file (or files, if you are using more than one management server). This must be done before the new SQL or API nodes can connect to the cluster.

It is not necessary to perform any restart of the cluster if new SQL or API nodes can employ previously unused API slots in the cluster configuration to connect to the cluster.

Restart types.  Information about the restart types used by the parameter descriptions in this section is shown in the following table:

Table 5.8 NDB Cluster restart types

Symbol	Restart Type	Description
N	Node	The parameter can be updated using a rolling restart (see Section 7.5, “Performing a Rolling Restart of an NDB Cluster”)
S	System	All cluster nodes must be shut down completely, then restarted, to effect a change in this parameter
I	Initial	Data nodes must be restarted using the --initial option