OPTIMIZE [NO_WRITE_TO_BINLOG | LOCAL] TABLE
    tbl_name [, tbl_name] ...

OPTIMIZE TABLE should be used if you have deleted a large part of a table or if you have made many changes to a table with variable-length rows (tables that have VARCHAR, VARBINARY, BLOB, or TEXT columns). Deleted rows are maintained in a linked list and subsequent INSERT operations reuse old row positions. You can use OPTIMIZE TABLE to reclaim the unused space and to defragment the data file.

This statement requires SELECT and INSERT privileges for the table.

Beginning with MySQL 5.1.27, OPTIMIZE TABLE is also supported for partitioned tables. Also beginning with MySQL 5.1.27, you can use ALTER TABLE ... OPTIMIZE PARTITION to optimize one or more partitions; for more information, see Section 12.1.7, “ALTER TABLE Syntax”, and Section 18.3.3, “Maintenance of Partitions”.

In most setups, you need not run OPTIMIZE TABLE at all. Even if you do a lot of updates to variable-length rows, it is not likely that you need to do this more than once a week or month and only on certain tables.

OPTIMIZE TABLE works only for MyISAM, InnoDB, and ARCHIVE tables. It does not work for tables created using any other storage engine, including NDBCLUSTER Disk Data tables.

Beginning with MySQL Cluster NDB 6.3.7, OPTIMIZE TABLE is supported for dynamic columns of in-memory NDBCLUSTER tables. The performance of OPTIMIZE on Cluster tables can be tuned by adjusting the value of the ndb_optimization_delay system variable, which controls the number of milliseconds to wait between processing batches of rows by OPTIMIZE TABLE. See Section 17.14.11, “Previous MySQL Cluster Issues Resolved in MySQL 5.1 and MySQL Cluster NDB 6.x”, for more information.

Beginning with MySQL Cluster NDB 6.3.8, OPTIMIZE TABLE can be interrupted by (for example) killing the SQL thread performing the OPTIMIZE operation.

For MyISAM tables, OPTIMIZE TABLE works as follows:

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. Beginning with MySQL 5.1.27, 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                                                          |
+----------+----------+----------+-------------------------------------------------------------------+
| test.foo | optimize | note     | Table does not support optimize, doing recreate + analyze instead | 
| test.foo | optimize | status   | OK                                                                | 
+----------+----------+----------+-------------------------------------------------------------------+

You can make OPTIMIZE TABLE work on other storage engines by starting mysqld with the --skip-new or --safe-mode option. In this case, OPTIMIZE TABLE is just mapped to ALTER TABLE.

OPTIMIZE TABLE returns a result set with the following columns:

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

By default, OPTIMIZE TABLE statements are written to the binary log so that they will be replicated to replication slaves. Logging can be suppressed with the optional NO_WRITE_TO_BINLOG keyword or its alias LOCAL.

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