mysql慢查询操作实例分析【开启、测试、确认等】

本文实例讲述了mysql慢查询操作。分享给大家供大家参考，具体如下：

mysql有些sql会执行很慢，有可能造成服务器负载飙升

首先查询 确定影响负载的是mysql ，使用top命令，ps命令等

其次，进入mysql，使用show full processlist查询执行中的sql语句，看看问题，使用explain 命令 查看状态

最后找出sql语句杀死或者优化

centos7上面安装mariadb服务

yum -y install mariadb-server mariadb-devel

开启慢查询

more /etc/my.cnf.d/server.cnf

[mariadb]
slow_query_log=on
slow_query_log_file=/usr/local/mysql/data/slow.log
long_query_time=1

启动mariadb服务

systemctl start mariadb

查询mysql的慢查询是否开启，以及多久的时间以上是慢查询

mariadb [(none)]> show variables like '%slow_query%';
+---------------------+--------------------------------+
| variable_name    | value             |
+---------------------+--------------------------------+
| slow_query_log   | on               |
| slow_query_log_file | /usr/local/mysql/data/slow.log |
+---------------------+--------------------------------+
2 rows in set (0.00 sec)

mariadb [(none)]> show variables like 'long_query_time';
+-----------------+----------+
| variable_name  | value  |
+-----------------+----------+
| long_query_time | 1.000000 |
+-----------------+----------+
1 row in set (0.00 sec)

#如果没用开启慢查询，可以在命令行开启
mysql> set global slow_query_log=1;
query ok, 0 rows affected (0.00 sec)

 测试慢查询，以及查看日志

mariadb [(none)]> select sleep(2);
+----------+
| sleep(2) |
+----------+
|    0 |
+----------+
1 row in set (2.00 sec)

[root@localhost ~]# more /usr/local/mysql/data/slow.log
/usr/libexec/mysqld, version: 5.5.60-mariadb (mariadb server). started with:
tcp port: 0 unix socket: /var/lib/mysql/mysql.sock
time         id command  argument
# time: 180930 23:51:07
# user@host: root[root] @ localhost []
# thread_id: 2 schema:  qc_hit: no
# query_time: 2.001017 lock_time: 0.000000 rows_sent: 1 rows_examined: 0
set timestamp=1538322667;
select sleep(2);

 确认慢查询

mariadb [(none)]> show full processlist; #查看state慢查询在进行
+----+------+-----------+------+---------+------+------------+-----------------------+----------+
| id | user | host   | db  | command | time | state   | info         | progress |
+----+------+-----------+------+---------+------+------------+-----------------------+----------+
| 3 | root | localhost | null | query  |  9 | user sleep | select sleep(10)   |  0.000 |
| 4 | root | localhost | null | query  |  0 | null    | show full processlist |  0.000 |
+----+------+-----------+------+---------+------+------------+-----------------------+----------+
2 rows in set (0.00 sec)

mariadb [(none)]> show full processlist; #查看state慢查询已经结束，但是用户登陆了
+----+------+-----------+------+---------+------+-------+-----------------------+----------+
| id | user | host   | db  | command | time | state | info         | progress |
+----+------+-----------+------+---------+------+-------+-----------------------+----------+
| 3 | root | localhost | null | sleep  |  1 |    | null         |  0.000 |
| 4 | root | localhost | null | query  |  0 | null | show full processlist |  0.000 |
+----+------+-----------+------+---------+------+-------+-----------------------+----------+
2 rows in set (0.00 sec)