mysql 正确安全清空在线慢查询日志slow log的流程

参考：http://blog.csdn.net/mchdba/article/details/19161097

1, see the slow log status;

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)    -- see the query time  mysql> show variables like '%long_query_time%';  +-----------------+----------+  | Variable_name   | Value    |  +-----------------+----------+  | long_query_time | 0.500000 |  +-----------------+----------+  1 row in set (0.00 sec)      mysql>   

2, stop the slow log server. 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)   3, reset the new path of slow log mysql> set global slow_query_log_file='/mysqllog/slow_log/slow_queries_3306_new.log';  Query OK, 0 rows affected (0.03 sec)   4, start the slow log server 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)   5, check the slow sql in the new slow log file. 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;   6, backup the old big slow log file to other directory. mv /mysqllog/slow_log/slow_queries_3306.log /mysqlbackup/slow_log/slow_queries_3306.log.bak.20140213