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
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)
更多关于MySQL相关内容感兴趣的读者可查看本站专题：《MySQL查询技巧大全》、《MySQL常用函数大汇总》、《MySQL日志操作技巧大全》、《MySQL事务操作技巧汇总》、《MySQL存储过程技巧大全》及《MySQL数据库锁相关技巧汇总》
希望本文所述对大家MySQL数据库计有所帮助。
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