To coalesce fragmented rows and eliminate wasted space that results from deleting or updating rows, run myisamchk in recovery mode:

shell> myisamchk -r tbl_name

You can optimize a table in the same way by using the OPTIMIZE TABLE SQL statement. OPTIMIZE TABLE does a table repair and a key analysis, and also sorts the index tree so that key lookups are faster. 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 12.5.2.5, “OPTIMIZE TABLE Syntax”.

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

For a full description of all available options, see Section 4.6.3, “myisamchk — MyISAM Table-Maintenance Utility”.