12.4.2.4. OPTIMIZE TABLE Syntax

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. After extensive changes to a table, this statement may also improve performance of statements that use the table, sometimes significantly.

This statement requires SELECT and INSERT privileges for the table.

OPTIMIZE TABLE is supported for partitioned tables, and you can use ALTER TABLE ... OPTIMIZE PARTITION to optimize one or more partitions; for more information, see Section 12.1.6, “ALTER TABLE Syntax”, and Section 18.3.3, “Maintenance of Partitions”.

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

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.

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                                                          |
+----------+----------+----------+-------------------------------------------------------------------+
| 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.

ColumnValue
TableThe table name
OpAlways optimize
Msg_typestatus, error, info, note, or warning
Msg_textAn informational message

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)

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