本文實例講述了mysql慢查詢操作。分享給大家供大家參考，具體如下：

mysql有些sql會執行很慢，有可能造成服務器負載飆升

首先查詢 確定影響負載的是mysql ，使用top命令，ps命令等

其次，進入MySQL，使用show full processlist查詢執行中的sql語句，看看問題，使用explain 命令 查看狀態

最后找出sql語句殺死或者優化

centos7上面安裝mariadb服務

yum -y install mariadb-server mariadb-devel

開啟慢查詢

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

[mariadb]slow_query_log=ONslow_query_log_file=/usr/local/mysql/data/slow.loglong_query_time=1

啟動mariadb服務

systemctl start mariadb

查詢mysql的慢查詢是否開啟，以及多久的時間以上是慢查詢

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)

#如果沒用開啟慢查詢，可以在命令行開啟mysql> set global slow_query_log=1;Query OK, 0 rows affected (0.00 sec)

 測試慢查詢，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.sockTime         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: 0SET timestamp=1538322667;select sleep(2);

 確認慢查詢

MariaDB [(none)]> show full processlist; #查看state慢查詢在進行+----+------+-----------+------+---------+------+------------+-----------------------+----------+| 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慢查詢已經結束，但是用戶登陸了+----+------+-----------+------+---------+------+-------+-----------------------+----------+| 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)