[b]1, see the slow log status;[/b] mysql> show variables like '%slow%'; +---------------------+------------------------------------------+ | Variable_name       | Value                                    | +---------------------+------------------------------------------+ | log_slow_queries    | ON                                       | | slow_launch_time    | 2                                        | | slow_query_log      | ON                                       | | slow_query_log_file | /mysqllog/slow_log/slow_queries_3306.log | +---------------------+------------------------------------------+ 4 rows in set (0.00 sec) [b]2, stop the slow log server.[/b] mysql> set global slow_query_log=0; Query OK, 0 rows affected (0.27 sec) mysql> show variables like '%slow%'; +---------------------+------------------------------------------+ | Variable_name       | Value                                    | +---------------------+------------------------------------------+ | log_slow_queries    | OFF                                      | | slow_launch_time    | 2                                        | | slow_query_log      | OFF                                      | | slow_query_log_file | /mysqllog/slow_log/slow_queries_3306.log | +---------------------+------------------------------------------+ 4 rows in set (0.00 sec) mysql> mysql> show variables like '%slow%'; -- check slow log status +---------------------+------------------------------------------+ | Variable_name       | Value                                    | +---------------------+------------------------------------------+ | log_slow_queries    | OFF                                      | | slow_launch_time    | 2                                        | | slow_query_log      | OFF                                      | | slow_query_log_file | /mysqllog/slow_log/slow_queries_3306.log | +---------------------+------------------------------------------+ 4 rows in set (0.00 sec) [b]3, reset the new path of slow log[/b] mysql> set global slow_query_log_file='/mysqllog/slow_log/slow_queries_3306_new.log'; Query OK, 0 rows affected (0.03 sec) [b]4, start the slow log server[/b] mysql> mysql> mysql> set global slow_query_log=1; Query OK, 0 rows affected (0.01 sec) mysql> show variables like '%slow%'; +---------------------+----------------------------------------------+ | Variable_name       | Value                                        | +---------------------+----------------------------------------------+ | log_slow_queries    | ON                                           | | slow_launch_time    | 2                                            | | slow_query_log      | ON                                           | | slow_query_log_file | /mysqllog/slow_log/slow_queries_3306_new.log | +---------------------+----------------------------------------------+ 4 rows in set (0.00 sec) [b]5, check the slow sql in the new slow log file.[/b] mysql> select sleep(10) as a, 1 as b; +---+---+ | a | b | +---+---+ | 0 | 1 | +---+---+ 1 row in set (10.00 sec) mysql> [mysql@xxx-xxx ~]$ more /mysqllog/slow_log/slow_queries_3306_new.log ...... Time                 Id Command    Argument # Time: 140213  6:44:24 # User@Host: root[root] @ localhost [] # Query_time: 10.000365  Lock_time: 0.000000 Rows_sent: 1  Rows_examined: 0 SET timestamp=1392273864; select sleep(10) as a, 1 as b; [b]6, backup the old big slow log file to other directory.[/b] mv /mysqllog/slow_log/slow_queries_3306.log /mysqlbackup/slow_log/slow_queries_3306.log.bak.20140213