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MySQL 5.0 Reference Manual :: 17 MySQL Cluster :: 17.12 Known Limitations of MySQL Cluster :: 17.12.2 Limits and Differences from Standard MySQL Limits
17.12.3 Limits Relating to Transaction Handling »
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17.12.2. Limits and Differences from Standard MySQL Limits

In this section, we list limits found in MySQL Cluster that either differ from limits found in, or that are not found in, standard MySQL.

  • Memory usage and recovery.  Memory comsumed when data is inserted into an NDB table is not automatically recovered when deleted, as it is with other storage engines. Instead, the following rules hold true:

    • A DELETE statement on an NDB table makes the memory formerly used by the deleted rows available for re-use by inserts on the same table only. This memory cannot be used by other NDB tables.

    • A DROP TABLE or TRUNCATE operation on an NDB table frees the memory that was used by this table for re-use by any NDB table, either by the same table or by another NDB table.

      Note

      Recall that TRUNCATE drops and re-creates the table. See Section 12.2.10, “TRUNCATE Syntax”.

      Memory freed by DELETE operations but still allocated to a specific table can also be made available for general re-use by performing a rolling restart of the cluster. See Section 17.5.1, “Performing a Rolling Restart of the Cluster”.

    • Limits imposed by the cluster's configuration.  A number of hard limits exist which are configurable, but available main memory in the cluster sets limits. See the complete list of configuration parameters in Section 17.3.4, “Configuration File”. Most configuration parameters can be upgraded online. These hard limits include:

      • Database memory size and index memory size (DataMemory and IndexMemory, respectively).

        DataMemory is allocated as 32KB pages. As each DataMemory page is used, it is assigned to a specific table; once allocated, this memory cannot be freed except by dropping the table.

        See Section 17.3.4.5, “Defining Data Nodes”, for further information about DataMemory and IndexMemory.

      • The maximum number of operations that can be performed per transaction is set using the configuration parameters MaxNoOfConcurrentOperations and MaxNoOfLocalOperations.

        Note

        Bulk loading, TRUNCATE TABLE, and ALTER TABLE are handled as special cases by running multiple transactions, and so are not subject to this limitation.

      • Different limits related to tables and indexes. For example, the maximum number of ordered indexes per table is determined by MaxNoOfOrderedIndexes.

    • Memory usage.  All Cluster table rows are of fixed length. This means (for example) that if a table has one or more VARCHAR fields containing only relatively small values, more memory and disk space is required when using the NDB storage engine than would be the case for the same table and data using the MyISAM engine. (In other words, in the case of a VARCHAR column, the column requires the same amount of storage as a CHAR column of the same size.)

    • Node and data object maximums.  The following limits apply to numbers of cluster nodes and metadata objects:

      • The maximum number of data nodes is 48.

        A data node must have a node ID in the range of 1‐49, inclusive. (Management and API nodes may use any integer in the range of 1‐63 inclusive as a node ID.)

      • The total maximum number of nodes in a MySQL Cluster is 63. This number includes all SQL nodes (MySQL Servers), API nodes (applications accessing the cluster other than MySQL servers), data nodes, and management servers.

      • The maximum number of metadata objects in MySQL 5.0 Cluster is 20320. This limit is hard-coded.