MySQL慢查询日志

查看是否开启慢查询功能

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mysql> show variables like 'slow_query%';
+---------------------+------------------------------------+
| Variable_name | Value |
+---------------------+------------------------------------+
| slow_query_log | OFF |
| slow_query_log_file | /var/lib/mysql/instance-1-slow.log |
+---------------------+------------------------------------+
2 rows in set (0.01 sec)
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mysql> show variables like 'long_query_time';
+-----------------+-----------+
| Variable_name | Value |
+-----------------+-----------+
| long_query_time | 10.000000 |
+-----------------+-----------+
1 row in set (0.00 sec)

说明:

  • slow_query_log 慢查询开启状态
  • slow_query_log_file 慢查询日志存放的位置(这个目录需要MySQL的运行帐号的可写权限,一般设置为MySQL的数据存放目录)
  • long_query_time 查询超过多少秒才记录

配置

临时配置

默认没有开启慢查询日志记录,通过命令临时开启:

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

mysql> set global slow_query_log_file='/var/lib/mysql/instance-1-slow.log';
Query OK, 0 rows affected (0.00 sec)

mysql> set global long_query_time=2;
Query OK, 0 rows affected (0.00 sec)

永久配置

修改配置文件达到永久配置状态:

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/etc/mysql/conf.d/mysql.cnf
[mysqld]
slow_query_log = ON
slow_query_log_file = /var/lib/mysql/instance-1-slow.log
long_query_time = 2

配置好后,重新启动 MySQL 即可。
测试
通过运行下面的命令,达到问题 SQL 语句的执行:

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mysql> select sleep(2);
+----------+
| sleep(2) |
+----------+
| 0 |
+----------+
1 row in set (2.00 sec)

然后查看慢查询日志内容:

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$ cat /var/lib/mysql/instance-1-slow.log
/usr/sbin/mysqld, Version: 8.0.13 (MySQL Community Server - GPL). started with:
Tcp port: 3306 Unix socket: /var/run/mysqld/mysqld.sock
Time Id Command Argument
/usr/sbin/mysqld, Version: 8.0.13 (MySQL Community Server - GPL). started with:
Tcp port: 3306 Unix socket: /var/run/mysqld/mysqld.sock
Time Id Command Argument
# Time: 2018-12-18T05:55:15.941477Z
# User@Host: root[root] @ localhost [] Id: 53
# Query_time: 2.000479 Lock_time: 0.000000 Rows_sent: 1 Rows_examined: 0
SET timestamp=1545112515;
select sleep(2);