MySQL数据库之慢查询日志

一、开启慢查询日志

通过show global variables like '%slow%' #查看MySQL慢查询日志是否开启

[root@mysqlmaster01 ~]# mysql --login-path=mysql57
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 21
Server version: 5.7.20-log MySQL Community Server (GPL)

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affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> show variables like '%slow%';
+---------------------------+----------+
| Variable_name | Value |
+---------------------------+----------+
| log_slow_admin_statements | OFF |
| log_slow_slave_statements | OFF |
| slow_launch_time | 2 |
| slow_query_log | ON |
| slow_query_log_file | slow.log |
+---------------------------+----------+
5 rows in set (0.01 sec)

• show variables like "long_query_time";  #查看MySQL慢查询时间设置，默认2秒（mysql5.7） 

mysql> show global variables like 'long%';
+-----------------+----------+
| Variable_name | Value |
+-----------------+----------+
| long_query_time | 2.000000 |
+-----------------+----------+
1 row in set (0.01 sec)

• log-queries-not-using-indexes = on  #记录未使用索引的查询

mysql> show global variables like '%queri%';
+----------------------------------------+-------+
| Variable_name | Value |
+----------------------------------------+-------+
| log_queries_not_using_indexes | OFF |
| log_throttle_queries_not_using_indexes | 0 |
+----------------------------------------+-------+
2 rows in set (0.00 sec)

mysql> show global variables like 'log%slow%';
+---------------------------+-------+
| Variable_name | Value |
+---------------------------+-------+
| log_slow_admin_statements | OFF |
| log_slow_slave_statements | OFF |
+---------------------------+-------+
2 rows in set (0.00 sec)

二） 安装mysqlsla分析慢查询日志

[root@mysqlmaster01 ~]#yum install  wget  perl  perl-DBI  perl-DBD-MySQL  mysql perl-ExtUtils-CBuilder perl-ExtUtils-MakeMaker cpan  perl-Time-HiRes

[root@mysqlmaster01 ~]# wget http://soft.51yuki.cn/mysqlsla-2.03.tar

[root@mysqlmaster01 ~]# tar xf mysqlsla-2.03.tar
[root@mysqlmaster01 ~]# cd mysqlsla-2.03

[root@mysqlmaster01 mysqlsla-2.03]# perl Makefile.PL
Checking if your kit is complete...
Looks good
Writing Makefile for mysqlsla
[root@mysqlmaster01 mysqlsla-2.03]# make && make install

案例：

#查询记录最多的20个sql语句，并写到select.log中去

mysqlsla -lt slow --sort t_sum --top 20  /data/mysql/127-slow.log >/tmp/select.log

#统计慢查询文件为/data/mysql/127-slow.log的所有select的慢查询sql，并显示执行时间最长的100条sql，并写到sql_select.log中去

mysqlsla -lt slow  -sf "+select" -top 100  /data/mysql/127-slow.log >/tmp/sql_select.log

#统计慢查询文件为/data/mysql/127-slow.log的数据库为mydata的所有select和update的慢查询sql，并查询次数最多的100条sql，并写到sql_num.sql中去

mysqlsla -lt slow  -sf "+select,update" -top 100 -sort c_sum  -db mydata /data/mysql/127-slow.log >/tmp/sql_num.log