MySQL :: MySQL 8.4 Reference Manual :: 15.7.3.4 OPTIMIZE TABLE Statement (original) (raw)

15.7.3.4 OPTIMIZE TABLE Statement

OPTIMIZE [NO_WRITE_TO_BINLOG | LOCAL]
    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 thestorage engine used by that table.

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

After doing substantial insert, update, or delete operations on an InnoDB table that has its own.ibd file because it was created with theinnodb_file_per_table option enabled. The table and indexes are reorganized, and disk space can be reclaimed for use by the operating system.
After doing substantial insert, update, or delete operations on columns that are part of a FULLTEXT index in an InnoDB table. Set the configuration optioninnodb_optimize_fulltext_only=1 first. To keep the index maintenance period to a reasonable time, set theinnodb_ft_num_word_optimize option to specify how many words to update in the search index, and run a sequence of OPTIMIZE TABLE statements until the search index is fully updated.
After deleting a large part of a MyISAM or ARCHIVE table, or making many changes to a MyISAM or ARCHIVEtable with variable-length rows (tables that haveVARCHAR,VARBINARY,BLOB, orTEXT columns). Deleted rows are maintained in a linked list and subsequentINSERT 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 works forInnoDB,MyISAM, andARCHIVE tables.OPTIMIZE TABLE is also supported for dynamic columns of in-memoryNDB 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, seeSection 25.2.7.11, “Previous NDB Cluster Issues Resolved in NDB Cluster 8.4”.

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 startingmysqld with the--skip-new option. In this case,OPTIMIZE TABLE is just mapped toALTER 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, seeSection 26.3.4, “Maintenance of Partitions”.

By default, the server writes OPTIMIZE TABLE statements to the binary log so that they replicate to replicas. To suppress logging, specify the optionalNO_WRITE_TO_BINLOG keyword or its aliasLOCAL. You must have theOPTIMIZE_LOCAL_TABLE privilege to use this option.

OPTIMIZE TABLE Output

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, orwarning
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.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 unlessmysqld is started by theroot user.

InnoDB Details

For InnoDB tables,OPTIMIZE TABLE is mapped toALTER TABLE ... FORCE, 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 anInnoDB 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                                                                |
+----------+----------+----------+-------------------------------------------------------------------+

OPTIMIZE TABLE usesonline DDL for regular and partitioned InnoDB tables, which reduces downtime for concurrent DML operations. The table rebuild triggered by OPTIMIZE TABLE is completed in place. An exclusive table lock is only taken briefly during the prepare phase and the commit phase of the operation. During the prepare phase, metadata is updated and an intermediate table is created. During the commit phase, table metadata changes are committed.

OPTIMIZE TABLE rebuilds the table using the table copy method under the following conditions:

When the old_alter_table system variable is enabled.
When the server is started with the--skip-new option.

OPTIMIZE TABLE usingonline DDL is not supported for InnoDB tables that containFULLTEXT indexes. The table copy method is used instead.

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

Some level of fragmentation is expected.InnoDB only fillspages 93% full, to leave room for updates without having to split pages.
Delete operations might leave gaps that leave pages less filled than desired, which could make it worthwhile to optimize the table.
Updates to rows usually rewrite the data within the same page, depending on the data type and row format, when sufficient space is available. SeeSection 17.9.1.5, “How Compression Works for InnoDB Tables” andSection 17.10, “InnoDB Row Formats”.
High-concurrency workloads might leave gaps in indexes over time, as InnoDB retains multiple versions of the same data due through itsMVCC mechanism. SeeSection 17.3, “InnoDB Multi-Versioning”.

MyISAM Details

For MyISAM tables,OPTIMIZE TABLE works as follows:

If the table has deleted or split rows, repair the table.
If the index pages are not sorted, sort them.
If the table's statistics are not up to date (and the repair could not be accomplished by sorting the index), update them.