Optimize table syntax-MySql database

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

If you have deleted a majority of the tables, or if you have made many changes to the tables that contain variable-length rows (tables that contain varchar, blob, or text columns, optimize table should be used. The deleted records are kept in the Link List. Subsequent insert operations will reuse the old record location. You can use optimize table to reuse unused space and organize data file fragments.

In most settings, you do not need to run optimize table. Even if you have made a large number of updates to a variable-length row, you do not need to run it frequently, once a week or once a month, and only run on a specific table.

Optimize table only applies to MyISAM, bdb, and InnoDB tables.

For MyISAM tables, optimize tables are operated as follows:

1. If the table has been deleted or broken down, the table will be repaired.

2. If the index page is not classified, the page is classified.

3. If the statistical data of the table is not updated (and cannot be repaired by classifying the index), update the data.

For bdb tables, optimize table is currently mapped to analyze table. For InnoDB tables, optimize table is mapped to alter table, which will recreate the table. The rebuilding operation can update index statistics and release unused space in the Cluster Index. See section 13.5.2.1 "analyze table Syntax ".

Use? Skip-new or? The safe-mode option can start mysqld. By starting mysqld, you can enable optimize table to work for other table types.

Note: During the optimize table operation, MySQL locks the table.

The optimize table statement is written to the binary log unless the optional NO_WRITE_TO_BINLOG keyword (or its alias is LOCAL) is used ). Therefore, the optimize table command for MySQL Server serves as a replication master server. By default, these commands will be copied to the replication slave server.