The time required to delete individual rows 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 Section 8.9.2, “Tuning Server Parameters”.

To delete all rows from a table, TRUNCATE TABLE tbl_name is faster than than DELETE FROM tbl_name. Truncate operations are not transaction-safe; an error occurs when attempting one in the course of an active transaction or active table lock. See Section 13.1.34, “TRUNCATE TABLE Syntax”.