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)