查看/设置“慢查询”的时间定义
mysql> show variables like "long%";
+-----------------+----------+
| Variable_name   | Value    |
+-----------------+----------+
| long_query_time | 1      |
+-----------------+----------+
1 row in set (0.00 sec)


如上述语句输出，“慢查询”的时间定义为1秒（方便测试，一般设置为1-10秒）。使用下面语句定义“慢查询”时间

mysql> set long_query_time=1;
Query OK, 0 rows affected (0.00 sec)


开启“慢查询”记录功能
mysql> show variables like "slow%";
+---------------------+------------------------------------+
| Variable_name       | Value                              |
+---------------------+------------------------------------+
| slow_launch_time    | 2                                  |
| slow_query_log      | OFF                                |
| slow_query_log_file | /opt/mysql/data/localhost-slow.log |
+---------------------+------------------------------------+
3 rows in set (0.00 sec)


上述语句查看“慢查询”的配置信息，你可以自定义日志文件的存放，但必须将 slow_query_log 全局变量设置为“ON”状态，执行以下语句：

mysql> set global slow_query_log=ON;
Query OK, 0 rows affected (0.01 sec)

结果：

mysql> show variables like "slow%";
+---------------------+------------------------------------+
| Variable_name       | Value                              |
+---------------------+------------------------------------+
| slow_launch_time    | 2                                  |
| slow_query_log      | ON                                 |
| slow_query_log_file | /opt/mysql/data/localhost-slow.log |
+---------------------+------------------------------------+
3 rows in set (0.00 sec)