21.2.7.1 Noncompliance with SQL Syntax in NDB Cluster

Some SQL statements relating to certain MySQL features produce errors when used with NDB tables, as described in the following list:

• Temporary tables.  Temporary tables are not supported. Trying either to create a temporary table that uses the NDB storage engine or to alter an existing temporary table to use NDB fails with the error Table storage engine 'ndbcluster' does not support the create option 'TEMPORARY'.

• Indexes and keys in NDB tables.  Keys and indexes on NDB Cluster tables are subject to the following limitations:

  • Column width.  Attempting to create an index on an NDB table column whose width is greater than 3072 bytes is rejected with ER_TOO_LONG_KEY: Specified key was too long; max key length is 3072 bytes.

    Attempting to create an index on an NDB table column whose width is greater than 3056 bytes succeeds with a warning. In such cases, statistical information is not generated, which means a nonoptimal execution plan may be selected. For this reason, you should consider making the index length shorter than 3056 bytes if possible.

  • TEXT and BLOB columns.  You cannot create indexes on NDB table columns that use any of the TEXT or BLOB data types.

  • FULLTEXT indexes.  The NDB storage engine does not support FULLTEXT indexes, which are possible for MyISAM and InnoDB tables only.

    However, you can create indexes on VARCHAR columns of NDB tables.

  • USING HASH keys and NULL.  Using nullable columns in unique keys and primary keys means that queries using these columns are handled as full table scans. To work around this issue, make the column NOT NULL, or re-create the index without the USING HASH option.

  • Prefixes.  There are no prefix indexes; only entire columns can be indexed. (The size of an NDB column index is always the same as the width of the column in bytes, up to and including 3072 bytes, as described earlier in this section. Also see Section 21.2.7.6, “Unsupported or Missing Features in NDB Cluster”, for additional information.)

  • BIT columns.  A BIT column cannot be a primary key, unique key, or index, nor can it be part of a composite primary key, unique key, or index.

  • AUTO_INCREMENT columns.  Like other MySQL storage engines, the NDB storage engine can handle a maximum of one AUTO_INCREMENT column per table, and this column must be indexed. However, in the case of an NDB table with no explicit primary key, an AUTO_INCREMENT column is automatically defined and used as a “hidden” primary key. For this reason, you cannot create an NDB table having an AUTO_INCREMENT column and no explicit primary key.

    The following CREATE TABLE statements do not work, as shown here:

    # No index on AUTO_INCREMENT column; table has no primary key
    # Raises ER_WRONG_AUTO_KEY
    mysql> CREATE TABLE n (
        ->     a INT,
        ->     b INT AUTO_INCREMENT
        ->     )
        -> ENGINE=NDB;
    ERROR 1075 (42000): Incorrect table definition; there can be only one auto
    column and it must be defined as a key 
    
    # Index on AUTO_INCREMENT column; table has no primary key
    # Raises NDB error 4335
    mysql> CREATE TABLE n (
        ->     a INT,
        ->     b INT AUTO_INCREMENT,
        ->     KEY k (b)
        ->     )
        -> ENGINE=NDB;
    ERROR 1296 (HY000): Got error 4335 'Only one autoincrement column allowed per
    table. Having a table without primary key uses an autoincr' from NDBCLUSTER

    The following statement creates a table with a primary key, an AUTO_INCREMENT column, and an index on this column, and succeeds:

    # Index on AUTO_INCREMENT column; table has a primary key
    mysql> CREATE TABLE n (
        ->     a INT PRIMARY KEY,
        ->     b INT AUTO_INCREMENT,
        ->     KEY k (b)
        ->     )
        -> ENGINE=NDB;
    Query OK, 0 rows affected (0.38 sec)

• Restrictions on foreign keys.  Support for foreign key constraints in NDB 7.5 is comparable to that provided by InnoDB, subject to the following restrictions:

  • Every column referenced as a foreign key requires an explicit unique key, if it is not the table's primary key.

  • ON UPDATE CASCADE is not supported when the reference is to the parent table's primary key.

    This is because an update of a primary key is implemented as a delete of the old row (containing the old primary key) plus an insert of the new row (with a new primary key). This is not visible to the NDB kernel, which views these two rows as being the same, and thus has no way of knowing that this update should be cascaded.

  • As of NDB 7.5.14 and NDB 7.6.10: ON DELETE CASCADE is not supported where the child table contains one or more columns of any of the TEXT or BLOB types. (Bug #89511, Bug #27484882)

  • SET DEFAULT is not supported. (Also not supported by InnoDB.)

  • The NO ACTION keywords are accepted but treated as RESTRICT. (Also the same as with InnoDB.)

  • In earlier versions of NDB Cluster, when creating a table with foreign key referencing an index in another table, it sometimes appeared possible to create the foreign key even if the order of the columns in the indexes did not match, due to the fact that an appropriate error was not always returned internally. A partial fix for this issue improved the error used internally to work in most cases; however, it remains possible for this situation to occur in the event that the parent index is a unique index. (Bug #18094360)

  • Prior to NDB 7.5.6, when adding or dropping a foreign key using ALTER TABLE, the parent table's metadata is not updated, which makes it possible subsequently to execute ALTER TABLE statements on the parent that should be invalid. To work around this issue, execute SHOW CREATE TABLE on the parent table immediately after adding or dropping the foreign key; this forces the parent's metadata to be reloaded.

    This issue is fixed in NDB 7.5.6. (Bug #82989, Bug #24666177)

  For more information, see Section 13.1.18.5, “FOREIGN KEY Constraints”, and Section 1.6.3.2, “FOREIGN KEY Constraints”.

• NDB Cluster and geometry data types.  Geometry data types (WKT and WKB) are supported for NDB tables. However, spatial indexes are not supported.

• Character sets and binary log files.  Currently, the ndb_apply_status and ndb_binlog_index tables are created using the latin1 (ASCII) character set. Because names of binary logs are recorded in this table, binary log files named using non-Latin characters are not referenced correctly in these tables. This is a known issue, which we are working to fix. (Bug #50226)

  To work around this problem, use only Latin-1 characters when naming binary log files or setting any the --basedir, --log-bin, or --log-bin-index options.

• Creating NDB tables with user-defined partitioning.  Support for user-defined partitioning in NDB Cluster is restricted to [LINEAR] KEY partitioning. Using any other partitioning type with ENGINE=NDB or ENGINE=NDBCLUSTER in a CREATE TABLE statement results in an error.

  It is possible to override this restriction, but doing so is not supported for use in production settings. For details, see User-defined partitioning and the NDB storage engine (NDB Cluster).

  Default partitioning scheme.  All NDB Cluster tables are by default partitioned by KEY using the table's primary key as the partitioning key. If no primary key is explicitly set for the table, the “hidden” primary key automatically created by the NDB storage engine is used instead. For additional discussion of these and related issues, see Section 22.2.5, “KEY Partitioning”.

  CREATE TABLE and ALTER TABLE statements that would cause a user-partitioned NDBCLUSTER table not to meet either or both of the following two requirements are not permitted, and fail with an error:

  1. The table must have an explicit primary key.

  2. All columns listed in the table's partitioning expression must be part of the primary key.

  Exception.  If a user-partitioned NDBCLUSTER table is created using an empty column-list (that is, using PARTITION BY [LINEAR] KEY()), then no explicit primary key is required.

  Maximum number of partitions for NDBCLUSTER tables.  The maximum number of partitions that can defined for a NDBCLUSTER table when employing user-defined partitioning is 8 per node group. (See Section 21.2.2, “NDB Cluster Nodes, Node Groups, Fragment Replicas, and Partitions”, for more information about NDB Cluster node groups.

  DROP PARTITION not supported.  It is not possible to drop partitions from NDB tables using ALTER TABLE ... DROP PARTITION. The other partitioning extensions to ALTER TABLE—ADD PARTITION, REORGANIZE PARTITION, and COALESCE PARTITION—are supported for NDB tables, but use copying and so are not optimized. See Section 22.3.1, “Management of RANGE and LIST Partitions” and Section 13.1.8, “ALTER TABLE Statement”.

  Partition selection.  Partition selection is not supported for NDB tables. See Section 22.5, “Partition Selection”, for more information.

• JSON data type.  The MySQL JSON data type is supported for NDB tables in the mysqld supplied with NDB 7.5.2 and later.

  An NDB table can have a maximum of 3 JSON columns.

  The NDB API has no special provision for working with JSON data, which it views simply as BLOB data. Handling data as JSON must be performed by the application.

• CPU and thread info ndbinfo tables.  NDB 7.5.2 adds several new tables to the ndbinfo information database providing information about CPU and thread activity by node, thread ID, and thread type. The tables are listed here:

  • cpustat: Provides per-second, per-thread CPU statistics

  • cpustat_50ms: Raw per-thread CPU statistics data, gathered every 50ms

  • cpustat_1sec: Raw per-thread CPU statistics data, gathered each second

  • cpustat_20sec: Raw per-thread CPU statistics data, gathered every 20 seconds

  • threads: Names and descriptions of thread types

  For more information about these tables, see Section 21.6.15, “ndbinfo: The NDB Cluster Information Database”.

• Lock info ndbinfo tables.  NDB 7.5.3 adds new tables to the ndbinfo information database providing information about locks and lock attempts in a running NDB Cluster. These tables are listed here:

  • cluster_locks: Current lock requests which are waiting for or holding locks; this information can be useful when investigating stalls and deadlocks. Analogous to cluster_operations.

  • locks_per_fragment: Counts of lock claim requests, and their outcomes per fragment, as well as total time spent waiting for locks successfully and unsuccessfully. Analogous to operations_per_fragment and memory_per_fragment.

  • server_locks: Subset of cluster transactions—those running on the local mysqld, showing a connection id per transaction. Analogous to server_operations.