linux下開啟mysql慢查詢，分析查詢語句
張映 發(fā)表于 2010-08-14
分類目錄： mysql
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一，為什么要開啟這個查詢呢？
數(shù)據(jù)庫是很容易產(chǎn)生瓶頸的地方，現(xiàn)在Nosql大家討論這么熱，估計都被數(shù)據(jù)庫搞郁悶了。mysql中最影響速度的就是那些查詢非常慢的語句，這些慢的語句，可能是寫的不夠合理或者是大數(shù)據(jù)下多表的聯(lián)合查詢等等，所以我們要找出這些語句，分析原因，加以優(yōu)化。這也是發(fā)這篇博文的原因
二，開啟mysql的慢查詢
方法1，用命令開啟慢查詢
查看復制打印?
- mysql> show variables like "%long%"; //查看一下默認為慢查詢的時間10秒
- +-----------------+-----------+
- | Variable_name | Value |
- +-----------------+-----------+
- | long_query_time | 10.000000 |
- +-----------------+-----------+
- 1 row in set (0.00 sec)
- mysql> set global long_query_time=2; //設置成2秒，加上global,下次進mysql已然生效
- Query OK, 0 rows affected (0.00 sec)
- mysql> show variables like "%slow%"; //查看一下慢查詢是不是已經(jīng)開啟
- +---------------------+---------------------------------+
- | Variable_name | Value |
- +---------------------+---------------------------------+
- | log_slow_queries | OFF |
- | slow_launch_time | 2 |
- | slow_query_log | OFF |
- | slow_query_log_file | /usr/local/mysql/mysql-slow.log |
- +---------------------+---------------------------------+
- 4 rows in set (0.00 sec)
- mysql> set slow_query_log='ON'; //加上global，不然會報錯的。
- ERROR 1229 (HY000): Variable 'slow_query_log' is a GLOBAL variable and should be set with SET GLOBAL
- mysql> set global slow_query_log='ON'; //啟用慢查詢
- Query OK, 0 rows affected (0.28 sec)
- mysql> show variables like "%slow%"; //查看是否已經(jīng)開啟
- +---------------------+---------------------------------+
- | Variable_name | Value |
- +---------------------+---------------------------------+
- | log_slow_queries | ON |
- | slow_launch_time | 2 |
- | slow_query_log | ON |
- | slow_query_log_file | /usr/local/mysql/mysql-slow.log |
- +---------------------+---------------------------------+
- 4 rows in set (0.00 sec)
方法2,修改mysql的配置文件my.cnf
在[mysqld]里面加上以下內容
- long_query_time = 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，其實就是把mysql-slow.log里面記錄下來的數(shù)據(jù)，分析一下顯示出來。其實自己寫一個shell腳本也是可以把要的信息取出來的。我們來看一下mysql-slow.log里面到底是什么東西
查看復制打印?
- [root@BlackGhost mysql]# cat mysql-slow.log //查看命令
- /usr/local/mysql/libexec/mysqld, Version: 5.1.26-rc-log (Source distribution). started with:
- Tcp port: 3306 Unix socket: /tmp/mysql.sock
- Time Id Command Argument
- # Time: 100814 13:28:30
- # User@Host: root[root] @ localhost []
- # Query_time: 10.096500 Lock_time: 0.045791 Rows_sent: 1 Rows_examined: 2374192
- SET timestamp=1281763710;
- 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);
- # Time: 100814 13:37:02
- # User@Host: root[root] @ localhost []
- # Query_time: 10.394134 Lock_time: 0.000091 Rows_sent: 1 Rows_examined: 2374192
- SET timestamp=1281764222;
- 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);
- # Time: 100814 13:37:16
- # User@Host: root[root] @ localhost []
- # Query_time: 4.608920 Lock_time: 0.000078 Rows_sent: 1 Rows_examined: 1260544
- SET timestamp=1281764236;
- 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，就是記錄一下sql語句的執(zhí)行情況，包括執(zhí)行時間，鎖定時間等，所以要不要分析工具看個人情況，分析工具很多，在這兒只說一下mysql自帶的慢查詢分析工具mysqldumpslow的使用方法。
查看復制打印?
- [root@BlackGhost bin]# mysqldumpslow -h
- Option h requires an argument
- ERROR: bad option
- Usage: mysqldumpslow [ OPTS... ] [ LOGS... ]
- Parse and summarize the MySQL slow query log. Options are
- --verbose verbose
- --debug debug
- --help write this text to standard output
- -v verbose
- -d debug //查錯
- -s ORDER what to sort by (t, at, l, al, r, ar etc), 'at' is default //排序方式query次數(shù)，時間，lock的時間和返回的記錄數(shù)來排序
- -r reverse the sort order (largest last instead of first) //倒排序
- -t NUM just show the top n queries //顯示前N多個
- -a don't abstract all numbers to N and strings to 'S'
- -n NUM abstract numbers with at least n digits within names //抽象的數(shù)字，至 少有n位內的名稱
- -g PATTERN grep: only consider stmts that include this string //配置模式
- -h HOSTNAME hostname of db server for *-slow.log filename (can be wildcard), //mysql所以機器名或者IP
- default is '*', i.e. match all
- -i NAME name of server instance (if using mysql.server startup script)
- -l don't subtract lock time from total time //總時間中不減去鎖定時間
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
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