3.14 Rebuilding or Repairing Tables or Indexes

This section describes how to rebuild or repair tables or indexes, which may be necessitated by:

• Changes to how MySQL handles data types or character sets. For example, an error in a collation might have been corrected, necessitating a table rebuild to update the indexes for character columns that use the collation.

• Required table repairs or upgrades reported by CHECK TABLE or mysqlcheck.

Methods for rebuilding a table include:

• Dump and Reload Method

• ALTER TABLE Method

• REPAIR TABLE Method

Dump and Reload Method

If you are rebuilding tables because a different version of MySQL cannot handle them after a binary (in-place) upgrade or downgrade, you must use the dump-and-reload method. Dump the tables before upgrading or downgrading using your original version of MySQL. Then reload the tables after upgrading or downgrading.

If you use the dump-and-reload method of rebuilding tables only for the purpose of rebuilding indexes, you can perform the dump either before or after upgrading or downgrading. Reloading still must be done afterward.

If you need to rebuild an InnoDB table because a CHECK TABLE operation indicates that a table upgrade is required, use mysqldump to create a dump file and mysql to reload the file. If the CHECK TABLE operation indicates that there is a corruption or causes InnoDB to fail, refer to Section 17.20.3, “Forcing InnoDB Recovery” for information about using the innodb_force_recovery option to restart InnoDB. To understand the type of problem that CHECK TABLE may be encountering, refer to the InnoDB notes in Section 15.7.3.2, “CHECK TABLE Statement”.

To rebuild a table by dumping and reloading it, use mysqldump to create a dump file and mysql to reload the file:

mysqldump db_name t1 > dump.sql
mysql db_name < dump.sql

To rebuild all the tables in a single database, specify the database name without any following table name:

mysqldump db_name > dump.sql
mysql db_name < dump.sql

To rebuild all tables in all databases, use the --all-databases option:

mysqldump --all-databases > dump.sql
mysql < dump.sql

ALTER TABLE Method

To rebuild a table with ALTER TABLE, use a “null” alteration; that is, an ALTER TABLE statement that “changes” the table to use the storage engine that it already has. For example, if t1 is an InnoDB table, use this statement:

ALTER TABLE t1 ENGINE = InnoDB;

If you are not sure which storage engine to specify in the ALTER TABLE statement, use SHOW CREATE TABLE to display the table definition.

REPAIR TABLE Method

The REPAIR TABLE method is only applicable to MyISAM, ARCHIVE, and CSV tables.

You can use REPAIR TABLE if the table checking operation indicates that there is a corruption or that an upgrade is required. For example, to repair a MyISAM table, use this statement:

REPAIR TABLE t1;

mysqlcheck --repair provides command-line access to the REPAIR TABLE statement. This can be a more convenient means of repairing tables because you can use the --databases or --all-databases option to repair all tables in specific databases or all databases, respectively:

mysqlcheck --repair --databases db_name ...
mysqlcheck --repair --all-databases