MySQL 5.5 Reference Manual Including MySQL NDB Cluster 7.2 Reference Guide OPTIMIZE TABLE Statement

    TABLE tbl_name [, tbl_name] ...

OPTIMIZE TABLE reorganizes the physical storage of table data and associated index data, to reduce storage space and improve I/O efficiency when accessing the table. The exact changes made to each table depend on the storage engine used by that table.

Use OPTIMIZE TABLE in these cases, depending on the type of table:

This statement requires SELECT and INSERT privileges for the table.

OPTIMIZE TABLE works for InnoDB, MyISAM, and ARCHIVE tables. OPTIMIZE TABLE is also supported for dynamic columns of in-memory NDB tables. It does not work for fixed-width columns of in-memory tables, nor does it work for Disk Data tables. The performance of OPTIMIZE on NDB Cluster tables can be tuned using --ndb-optimization-delay, which controls the length of time to wait between processing batches of rows by OPTIMIZE TABLE. For more information, see Section, “Previous NDB Cluster Issues Resolved in MySQL 5.1, NDB Cluster 6.x, and NDB Cluster 7.x”.

For NDB Cluster tables, OPTIMIZE TABLE can be interrupted by (for example) killing the SQL thread performing the OPTIMIZE operation.

By default, OPTIMIZE TABLE does not work for tables created using any other storage engine and returns a result indicating this lack of support. You can make OPTIMIZE TABLE work for other storage engines by starting mysqld with the --skip-new option. In this case, OPTIMIZE TABLE is just mapped to ALTER TABLE.

This statement does not work with views.

OPTIMIZE TABLE is supported for partitioned tables. For information about using this statement with partitioned tables and table partitions, see Section 19.3.3, “Maintenance of Partitions”.

By default, the server writes OPTIMIZE TABLE statements to the binary log so that they replicate to replication slaves. To suppress logging, specify the optional NO_WRITE_TO_BINLOG keyword or its alias LOCAL.


OPTIMIZE TABLE returns a result set with the columns shown in the following table.

Column Value
Table The table name
Op Always optimize
Msg_type status, error, info, note, or warning
Msg_text An informational message

OPTIMIZE TABLE table catches and throws any errors that occur while copying table statistics from the old file to the newly created file. For example. if the user ID of the owner of the .frm, .MYD, or .MYI file is different from the user ID of the mysqld process, OPTIMIZE TABLE generates a "cannot change ownership of the file" error unless mysqld is started by the root user.

InnoDB Details

For InnoDB tables, OPTIMIZE TABLE is mapped to ALTER TABLE, which rebuilds the table to update index statistics and free unused space in the clustered index. This is displayed in the output of OPTIMIZE TABLE when you run it on an InnoDB table, as shown here:

mysql> OPTIMIZE TABLE foo;
| Table    | Op       | Msg_type | Msg_text                                                          |
| | optimize | note     | Table does not support optimize, doing recreate + analyze instead |
| | optimize | status   | OK                                                                |

This operation does not use fast index creation. Secondary indexes are not created as efficiently because keys are inserted in the order they appeared in the primary key. See Section 14.16.6, “Limitations of Fast Index Creation”.

InnoDB stores data using a page-allocation method and does not suffer from fragmentation in the same way that legacy storage engines (such as MyISAM) will. When considering whether or not to run optimize, consider the workload of transactions that your server will process:

MyISAM Details

For MyISAM tables, OPTIMIZE TABLE works as follows:

  1. If the table has deleted or split rows, repair the table.

  2. If the index pages are not sorted, sort them.

  3. If the table's statistics are not up to date (and the repair could not be accomplished by sorting the index), update them.

Other Considerations

Note that MySQL locks the table during the time OPTIMIZE TABLE is running.

OPTIMIZE TABLE does not sort R-tree indexes, such as spatial indexes on POINT columns. (Bug #23578)