mysql慢查询日志功能的使用

作用：mysql慢查询日志可监控有效率问题的SQL 。、

一、开启mysql慢查询日志功能

1、查看是否开启 未使用索引的SQL记录日志查询

mysql> show variables like 'log_queries_not_using_indexes';
+-------------------------------+-------+
| Variable_name                 | Value |
+-------------------------------+-------+
| log_queries_not_using_indexes | OFF   |
+-------------------------------+-------+
1 row in set (0.00 sec)

开启 未使用索引的SQL记录日志查询

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

mysql> show variables like 'log_queries_not_using_indexes';
+-------------------------------+-------+
| Variable_name                 | Value |
+-------------------------------+-------+
| log_queries_not_using_indexes | ON    |
+-------------------------------+-------+
1 row in set (0.00 sec)

2、查看超过多长时间的查询记入慢查询日志中

mysql> show variables like 'long_query_time';
+-----------------+-----------+
| Variable_name   | Value     |
+-----------------+-----------+
| long_query_time | 10.000000 |
+-----------------+-----------+
1 row in set (0.00 sec)

默认10s，为做测试，修改为0，即记录所有。

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

ps：需要断开重新连接，才会查看到更新的状态

mysql> show variables like 'long_query_time';
+-----------------+----------+
| Variable_name   | Value    |
+-----------------+----------+
| long_query_time | 0.000000 |
+-----------------+----------+
1 row in set (0.00 sec)

3、查看是否开启 mysql慢查询日志功能

mysql> show variables like 'slow_query_log';
+----------------+-------+
| Variable_name  | Value |
+----------------+-------+
| slow_query_log | OFF   |
+----------------+-------+
1 row in set (0.01 sec)

 开启慢查询日志功能 

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

mysql> show variables like 'slow_query_log';
+----------------+-------+
| Variable_name  | Value |
+----------------+-------+
| slow_query_log | ON    |
+----------------+-------+
1 row in set (0.01 sec)

4、查看日志记录位置

mysql> show variables like 'slow_query_log_file';
+---------------------+--------------------------------------+
| Variable_name       | Value                                |
+---------------------+--------------------------------------+
| slow_query_log_file | /usr/local/mysql/data/bogon-slow.log |
+---------------------+--------------------------------------+
1 row in set (0.00 sec)

5、执行若干SQL语句，看是否记入日志

查看最后20条记录如下，成功记录了最后20条SQL执行语句。

[root@bogon ~]# tail -20 /usr/local/mysql/data/bogon-slow.log 
# Time: 190115 17:46:21
# User@Host: root[root] @ localhost []
# Query_time: 0.000329  Lock_time: 0.000166 Rows_sent: 40  Rows_examined: 40
SET timestamp=1547545581;
show tables;
# Time: 190115 17:46:36
# User@Host: root[root] @ localhost []
# Query_time: 0.054437  Lock_time: 0.000115 Rows_sent: 104  Rows_examined: 104
SET timestamp=1547545596;
select * from TABLES;
# Time: 190115 17:49:12
# User@Host: root[root] @ localhost []
# Query_time: 0.001611  Lock_time: 0.000705 Rows_sent: 21  Rows_examined: 21
SET timestamp=1547545752;
desc TAbles;
# Time: 190115 17:49:41
# User@Host: root[root] @ localhost []
# Query_time: 0.002142  Lock_time: 0.000056 Rows_sent: 104  Rows_examined: 104
SET timestamp=1547545781;
select VERSION from Tables;

6、慢查日志的存储格式

主要有五部分组成

# Time: 190115 17:54:44                                                      执行时间
# User@Host: root[root] @ localhost []                                       执行主机        
# Query_time: 0.000073  Lock_time: 0.000000 Rows_sent: 1  Rows_examined: 0   执行信息
SET timestamp=1547546084;                                                    时间戳
select database();                                                           执行语句

 二、慢查询日志分析工具

1、mysql自带的 mysqldumpslow工具

使用mysqldumpslow查看最近6条记录

[root@bogon ~]# mysqldumpslow -t 6 /usr/local/mysql/data/bogon-slow.log 

Reading mysql slow query log from /usr/local/mysql/data/bogon-slow.log
Count: 1  Time=0.05s (0s)  Lock=0.00s (0s)  Rows=104.0 (104), root[root]@localhost
  select * from TABLES

Count: 1  Time=0.01s (0s)  Lock=0.00s (0s)  Rows=0.0 (0), root[root]@localhost
  select databas()

Count: 1  Time=0.00s (0s)  Lock=0.00s (0s)  Rows=104.0 (104), root[root]@localhost
  select VERSION from Tables

Count: 1  Time=0.00s (0s)  Lock=0.00s (0s)  Rows=21.0 (21), root[root]@localhost
  desc TAbles

Count: 2  Time=0.00s (0s)  Lock=0.00s (0s)  Rows=1.0 (2), root[root]@localhost
  show variables like 'S'

Count: 2  Time=0.00s (0s)  Lock=0.00s (0s)  Rows=40.0 (80), root[root]@localhost
  show tables

 2、pt-query-digest分析工具

1）安装

[root@bogon ~]# wget wget percona.com/get/pt-query-digest

[root@bogon ~]# chmod u+x pt-query-digest

[root@bogon ~]# mv /root/pt-query-digest /usr/bin/

2）启动出现错误提示

[root@bogon bin]# pt-query-digest --help
Can't locate Digest/MD5.pm in @INC (@INC contains: /usr/local/lib64/perl5 /usr/local/share/perl5 /usr/lib64/perl5/vendor_perl 
/usr/share/perl5/vendor_perl /usr/lib64/perl5 /usr/share/perl5 .) at /usr/bin/pt-query-digest line 2470.
BEGIN failed--compilation aborted at /usr/bin/pt-query-digest line 2470.

安装perl-Digest-MD5即可

[root@bogon bin]# yum install perl-Digest-MD5