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linux下开启mysql慢查询,分析查询语句

时间:2021-07-01 10:21:17 帮助过:17人阅读

一,为什么要开启这个查询呢? 数据库是很容易产生瓶颈的地方,现在Nosql大家讨论这么热,估计都被数据库搞郁闷了。mysql中最影响速度的就是那些查询非常慢的语句,这些慢的语句,可能是写的不够合理或者是大数据下多表的联合查询等等,所以我们要找出这些语

一,为什么要开启这个查询呢?

数据库是很容易产生瓶颈的地方,现在Nosql大家讨论这么热,估计都被数据库搞郁闷了。mysql中最影响速度的就是那些查询非常慢的语句,这些慢的语句,可能是写的不够合理或者是大数据下多表的联合查询等等,所以我们要找出这些语句,分析原因,加以优化。这也是发这篇博文的原因

二,开启mysql的慢查询

方法1,用命令开启慢查询

查看复制打印?

  1. mysql> show variables like "%long%"; //查看一下默认为慢查询的时间10秒
  2. +-----------------+-----------+
  3. | Variable_name | Value |
  4. +-----------------+-----------+
  5. | long_query_time | 10.000000 |
  6. +-----------------+-----------+
  7. 1 row in set (0.00 sec)
  8. mysql> set global long_query_time=2; //设置成2秒,加上global,下次进mysql已然生效
  9. Query OK, 0 rows affected (0.00 sec)
  10. mysql> show variables like "%slow%"; //查看一下慢查询是不是已经开启
  11. +---------------------+---------------------------------+
  12. | Variable_name | Value |
  13. +---------------------+---------------------------------+
  14. | log_slow_queries | OFF |
  15. | slow_launch_time | 2 |
  16. | slow_query_log | OFF |
  17. | slow_query_log_file | /usr/local/mysql/mysql-slow.log |
  18. +---------------------+---------------------------------+
  19. 4 rows in set (0.00 sec)
  20. mysql> set slow_query_log='ON'; //加上global,不然会报错的。
  21. ERROR 1229 (HY000): Variable 'slow_query_log' is a GLOBAL variable and should be set with SET GLOBAL
  22. mysql> set global slow_query_log='ON'; //启用慢查询
  23. Query OK, 0 rows affected (0.28 sec)
  24. mysql> show variables like "%slow%"; //查看是否已经开启
  25. +---------------------+---------------------------------+
  26. | Variable_name | Value |
  27. +---------------------+---------------------------------+
  28. | log_slow_queries | ON |
  29. | slow_launch_time | 2 |
  30. | slow_query_log | ON |
  31. | slow_query_log_file | /usr/local/mysql/mysql-slow.log |
  32. +---------------------+---------------------------------+
  33. 4 rows in set (0.00 sec)

方法2,修改mysql的配置文件my.cnf

在[mysqld]里面加上以下内容

  1. long_query_time = 2
  2. log-slow-queries = /usr/local/mysql/mysql-slow.log

重起一下
/usr/local/mysql/libexec/mysqld restart

三,分析工具

分析工具干什么事的呢,其实就是把mysql-slow.log里面记录下来的数据,分析一下显示出来。其实自己写一个shell脚本也是可以把要的信息取出来的。我们来看一下mysql-slow.log里面到底是什么东西

查看复制打印?

  1. [root@BlackGhost mysql]# cat mysql-slow.log //查看命令
  2. /usr/local/mysql/libexec/mysqld, Version: 5.1.26-rc-log (Source distribution). started with:
  3. Tcp port: 3306 Unix socket: /tmp/mysql.sock
  4. Time Id Command Argument
  5. # Time: 100814 13:28:30
  6. # User@Host: root[root] @ localhost []
  7. # Query_time: 10.096500 Lock_time: 0.045791 Rows_sent: 1 Rows_examined: 2374192
  8. SET timestamp=1281763710;
  9. select count(distinct ad_code) as x from ad_visit_history where ad_code in (select ad_code from ad_list where media_id=15);
  10. # Time: 100814 13:37:02
  11. # User@Host: root[root] @ localhost []
  12. # Query_time: 10.394134 Lock_time: 0.000091 Rows_sent: 1 Rows_examined: 2374192
  13. SET timestamp=1281764222;
  14. select count(distinct ad_code) as x from ad_visit_history where ad_code in (select ad_code from ad_list where media_id=15);
  15. # Time: 100814 13:37:16
  16. # User@Host: root[root] @ localhost []
  17. # Query_time: 4.608920 Lock_time: 0.000078 Rows_sent: 1 Rows_examined: 1260544
  18. SET timestamp=1281764236;
  19. select count(*) as cou from ad_visit_history where ad_code in (select ad_code from ad_list where id=41) order by id desc;

看到了,就是记录一下sql语句的执行情况,包括执行时间,锁定时间等,所以要不要分析工具看个人情况,分析工具很多,在这儿只说一下mysql自带的慢查询分析工具mysqldumpslow的使用方法。

查看复制打印?

  1. [root@BlackGhost bin]# mysqldumpslow -h
  2. Option h requires an argument
  3. ERROR: bad option
  4. Usage: mysqldumpslow [ OPTS... ] [ LOGS... ]
  5. Parse and summarize the MySQL slow query log. Options are
  6. --verbose verbose
  7. --debug debug
  8. --help write this text to standard output
  9. -v verbose
  10. -d debug //查错
  11. -s ORDER what to sort by (t, at, l, al, r, ar etc), 'at' is default //排序方式query次数,时间,lock的时间和返回的记录数来排序
  12. -r reverse the sort order (largest last instead of first) //倒排序
  13. -t NUM just show the top n queries //显示前N多个
  14. -a don't abstract all numbers to N and strings to 'S'
  15. -n NUM abstract numbers with at least n digits within names //抽象的数字,至 少有n位内的名称
  16. -g PATTERN grep: only consider stmts that include this string //配置模式
  17. -h HOSTNAME hostname of db server for *-slow.log filename (can be wildcard), //mysql所以机器名或者IP
  18. default is '*', i.e. match all
  19. -i NAME name of server instance (if using mysql.server startup script)
  20. -l don't subtract lock time from total time //总时间中不减去锁定时间

例子:

[root@BlackGhost bin]# ./mysqldumpslow -s r -t 20 /usr/local/mysql/mysql-slow.log

[root@BlackGhost bin]# ./mysqldumpslow -s r -t 20 -g 'count' /usr/local/mysql/mysql-slow.log


-----整理自网上

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