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12.5.2.5. OPTIMIZE TABLE Syntax

OPTIMIZE [LOCAL | NO_WRITE_TO_BINLOG] 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.

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, BDB, and InnoDB 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 BDB tables, OPTIMIZE TABLE currently is mapped to ANALYZE TABLE. See Section 12.5.2.1, “ANALYZE TABLE Syntax”.

That was also the case for InnoDB tables before MySQL 4.1.3. As of 4.1.3, OPTIMIZE TABLE is mapped to ALTER TABLE, which rebuilds the table to update index statistics and free unused space in the clustered index.

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:

Column Value
Table The table name
Op Always optimize
Msg_type One of status, error, info, or warning
Msg_text The message

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

Before MySQL 4.1.1, OPTIMIZE TABLE statements are not written to the binary log. As of MySQL 4.1.1, OPTIMIZE TABLE statements are written to the binary log so that such statements used on a MySQL server acting as a replication master will be replicated to replication slaves. Logging can be suppressed with the optional NO_WRITE_TO_BINLOG keyword or its alias LOCAL.


User Comments

Posted by Dathan Pattishall on May 25 2004 4:41pm[Delete] [Edit]

myisamchk --quick --check-only-changed --sort-index --analyze

do a myisamchk on the table.
--
notice the deleted blocks in the right hand corner of the dialog. The stat still indicates a number > 0 for tables with deleted blocks.

===
myisamchk -r --sort-index --analyze *.MYI fixes that number. I'm inclined to believe the myisamchk *.MYI number since the table I'm "optimizing" does get a lot of deletes.


ALTER TABLE [tbl_name] TYPE=innodb
- will OPTIMIZE an INNODB table in the table space as well

Posted by Michael Grabenstein on April 28 2004 6:55pm[Delete] [Edit]

In case you programatically only want to optimize if the data_free (deleted) is some percentage of your data length (size) you can find that out via this statement:
show table status
http://dev.mysql.com/doc/mysql/en/SHOW_TABLE_STATUS.html

Also myisamchk -d has similar.

Posted by Jeremy Tinley on August 11 2004 5:24pm[Delete] [Edit]

This page does not tell you what type of database privileges you need to execute OPTIMIZE TABLES.

You need SELECT and INSERT permissions to optimize a table.

Posted by Mihail Manolov on October 29 2004 6:00pm[Delete] [Edit]

Don't forget to FLUSH TABLES after execution of any of the following - REPAIR TABLE, TRUNCATE TABLE, OPTIMIZE TABLE, or ANALYZE TABLE on tables that are mapped into MERGE table.

Posted by James Day on November 28 2004 10:47pm[Delete] [Edit]

For InnoDB, if you have your tables in one tablespace, this will make a complete copy of the table within the tablespace, making the tablespace larger by the total table size less the free space you started with. It will not reduce the tablespace size. It can free fragmented space within a table to the tablespace, making that space available to other tables. If you're short of disk space and don't want to enlarge the tablespace you may be able to work around this by altering the table to MyISAM and then back to InnoDB.

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