To coalesce fragmented rows and eliminate wasted space that results from deleting or updating rows, run myisamchk in recovery mode:
$> 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
TABLE. See OPTIMIZE TABLE Statement.
myisamchk has a number of other options that you can use to improve the performance of a table:
-a: Perform key distribution analysis. This improves join performance by enabling the join optimizer to better choose the order in which to join the tables and which indexes it should use.
-S: Sort the index blocks. This optimizes seeks and makes table scans that use indexes faster.
-R: Sort data rows according to a given index. This makes your data much more localized and may speed up range-based
ORDER BYoperations that use this index.
For a full description of all available options, see myisamchk — MyISAM Table-Maintenance Utility.