MySQL慢查询

MySQL慢查询对查找性能瓶颈的SQL很有用，下面来看看如何开启MySQL慢查询操作：

[root@yunuo_vm ~]# mysql -u root -pEnter password:Welcome to the MySQL monitor. Commands end with ; or \g.Your MySQL connection id is 4977Server version: 5.6.17 Source distribution Copyright (c) 2000, 2014, Oracle and/or its affiliates. All rights reserved. Oracle is a registered trademark of Oracle Corporation and/or itsaffiliates. Other names may be trademarks of their respectiveowners. Type 'help;' or '\h' for help. Type '\c' to clear the current input statement. mysql>

ps:这里的MySQL版本是5.6.17

OK,进入到控制台了,接下来，我们查看下MySQL默认配置中多少秒才算慢查询

mysql> show variables like 'long%';+-----------------+-----------+| Variable_name  | Value   |+-----------------+-----------+| long_query_time | 10.000000 |+-----------------+-----------+1 row in set (0.00 sec)

如上表显示，系统默认的慢查询时间上限是10秒，下面我们来把它改成1秒(大家也可以根据自己实际情况来定)；

mysql> set long_query_time=1;  注： 我设置了1, 也就是执行时间超过1秒的都算慢查询。Query OK, 0 rows affected (0.00 sec)

哦了！最后我们来瞅瞅MySQL开启慢查询日志记录没有；

mysql> show variables like 'slow%';+---------------------+---------------+| Variable_name    | Value     |+---------------------+---------------+| slow_launch_time  | 2       | | slow_query_log   | OFF      || slow_query_log_file | /tmp/slow.log |+---------------------+---------------+

ps:

slow_query_log //是否打开日志记录

slow_query_log_file //日志存放位置

MySQL默认没有开启慢查询，下面我们来开启下：

mysql> set global slow_query_log='ON';Query OK, 0 rows affected (0.00 sec)