MySQL Reference Manual :: 5.8.3.10 Table Optimization

To coalesce fragmented records and eliminate wasted space resulting from deleting or updating records, run myisamchk in recovery mode:

shell> myisamchk -r tbl_name

You can optimize a table in the same way by using the SQL OPTIMIZE TABLE statement. OPTIMIZE TABLE does a repair of the table and a key analysis, and also sorts the index tree to give faster key lookups. There is also no possibility of unwanted interaction between a utility and the server, because the server does all the work when you use OPTIMIZE TABLE. See Section 13.5.2.5, “OPTIMIZE TABLE Syntax”.

myisamchk also has a number of other options you can use to improve the performance of a table:

For a full description of the options, see Section 5.8.3.1, “myisamchk Invocation Syntax”.