2.6. Limitations

Take the following considerations into account when creating or dropping indexes using the InnoDB Plugin:

  • During index creation, files are written to the temporary directory ($TMPDIR on Unix, %TEMP% on Windows, or the value of --tmpdir configuration variable). Each temporary file is large enough to hold one column that makes up the new index, and each one is removed as soon as it is merged into the final index.

  • Due to a limitation of MySQL, the table is copied, rather than using Fast Index Creation when you create an index on a TEMPORARY TABLE. This has been reported as MySQL Bug #39833.

  • To avoid consistency issues between the InnoDB data dictionary and the MySQL data dictionary, the table is copied, rather than using Fast Index Creation when you use the ALTER TABLE ... RENAME COLUMN syntax.

  • The command ALTER IGNORE TABLE t ADD UNIQUE INDEX does not delete duplicate rows. This has been reported as MySQL Bug #40344. The IGNORE keyword is ignored. If any duplicate rows exist, the operation fails with the following error message:

    ERROR 23000: Duplicate entry '347' for key 'pl'
  • As noted above, a newly-created index contains only information about data current at the time the index was created. Therefore, you should not run queries in a transaction that might use a secondary index that did not exist at the beginning of the transaction. There is no way for InnoDB to access old data that is consistent with the rest of the data read by the transaction. See the discussion of locking in Section 2.4, “Concurrency Considerations”.

    Prior to InnoDB Plugin 1.0.4, unexpected results could occur if a query attempts to use an index created after the start of the transaction containing the query. If an old transaction attempts to access a too new index, InnoDB Plugin 1.0.4 and later reports an error:

    ERROR HY000: Table definition has changed, please retry transaction

    As the error message suggests, committing (or rolling back) the transaction, and restarting it, cures the problem.

  • InnoDB Plugin 1.0.2 introduces some improvements in error handling when users attempt to drop indexes. See section Section 8.7, “Better Error Handling when Dropping Indexes” for details.

  • MySQL 5.1 does not support efficient creation or dropping of FOREIGN KEY constraints. Therefore, if you use ALTER TABLE to add or remove a REFERENCES constraint, the child table will be copied, rather than using Fast Index Creation.

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