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The time required to delete individual rows in aMyISAM 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 thekey_buffer_size system variable. SeeSection 7.1.1, “Configuring the Server”.

To delete all rows from aMyISAM table,TRUNCATE TABLEtbl_name is faster thanDELETE FROMtbl_name. Truncate operations are not transaction-safe; an error occurs when attempting one in the course of an active transaction or active table lock. SeeSection 15.1.39, “TRUNCATE TABLE Statement”.