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22.1.7.6 Unsupported or Missing Features in NDB Cluster

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A number of features supported by other storage engines are not supported for NDB tables. Trying to use any of these features in NDB Cluster does not cause errors in or of itself; however, errors may occur in applications that expects the features to be supported or enforced. Statements referencing such features, even if effectively ignored by NDB, must be syntactically and otherwise valid.

  • Index prefixes.  Prefixes on indexes are not supported for NDB tables. If a prefix is used as part of an index specification in a statement such as CREATE TABLE, ALTER TABLE, or CREATE INDEX, the prefix is not created by NDB.

    A statement containing an index prefix, and creating or modifying an NDB table, must still be syntactically valid. For example, the following statement always fails with Error 1089 Incorrect prefix key; the used key part isn't a string, the used length is longer than the key part, or the storage engine doesn't support unique prefix keys, regardless of storage engine:

    1. CREATE TABLE t1 (
    2.     c1 INT NOT NULL,
    3.     c2 VARCHAR(100),
    4.     INDEX i1 (c2(500))
    5. );

    This happens on account of the SQL syntax rule that no index may have a prefix larger than itself.

  • Savepoints and rollbacks.  Savepoints and rollbacks to savepoints are ignored as in MyISAM.

  • Durability of commits.  There are no durable commits on disk. Commits are replicated, but there is no guarantee that logs are flushed to disk on commit.

  • Replication.  Statement-based replication is not supported. Use --binlog-format=ROW (or --binlog-format=MIXED) when setting up cluster replication. See Section 22.6, “NDB Cluster Replication”, for more information.

    Replication using global transaction identifiers (GTIDs) is not compatible with NDB Cluster, and is not supported in NDB Cluster 8.0. Do not enable GTIDs when using the NDB storage engine, as this is very likely to cause problems up to and including failure of NDB Cluster Replication.

    Semisynchronous replication is not supported in NDB Cluster.

  • Generated columns.  The NDB storage engine does not support indexes on virtual generated columns.

    As with other storage engines, you can create an index on a stored generated column, but you should bear in mind that NDB uses DataMemory for storage of the generated column as well as IndexMemory for the index. See JSON columns and indirect indexing in NDB Cluster, for an example.

    NDB Cluster writes changes in stored generated columns to the binary log, but does log not those made to virtual columns. This should not effect NDB Cluster Replication or replication between NDB and other MySQL storage engines.

Note

See Section 22.1.7.3, “Limits Relating to Transaction Handling in NDB Cluster”, for more information relating to limitations on transaction handling in NDB.


Rechercher dans le manuel MySQL

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Document créé le 26/06/2006, dernière modification le 26/10/2018
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