Speed of DELETE Statements
The time required to delete individual rows in a MyISAM table is exactly proportional to the number of indexes. To delete rows more quickly, you can increase the size of the key cache by increasing the key_buffer_size system variable. See , "Tuning Server Parameters".
To delete all rows from a MyISAM table, TRUNCATE TABLE is faster than than tbl_nameDELETE FROM . Truncate operations are not transaction-safe; an error occurs when attempting one in the course of an active transaction or active table lock. See , "tbl_nameTRUNCATE TABLE Syntax".