MySQL慢查询查找和调优测试

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我是靠谱客的博主专注衬衫，最近开发中收集的这篇文章主要介绍MySQL慢查询查找和调优测试，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

编辑 my.cnf或者my.ini文件，去除下面这几行代码的注释：

复制代码代码如下:

 
log_slow_queries = /var/log/mysql/mysql-slow.log 
long_query_time = 2 
log-queries-not-using-indexes 

这将使得慢查询和没有使用索引的查询被记录下来。
这样做之后，对mysql-slow.log文件执行tail -f命令，将能看到其中记录的慢查询和未使用索引的查询。
随便提取一个慢查询，执行explain：

复制代码代码如下:

explain low_query

复制代码代码如下:

 
SELECT t.TABLE_SCHEMA AS `db`, 
t.TABLE_NAME AS `table`, 
s.INDEX_NAME AS `index name`, 
s.COLUMN_NAME AS `FIELD name`, 
s.SEQ_IN_INDEX `seq IN index`, 
s2.max_columns AS `# cols`, 
s.CARDINALITY AS `card`, 
t.TABLE_ROWS AS `est rows`, 
ROUND(((s.CARDINALITY / IFNULL(t.TABLE_ROWS, 0.01)) * 100), 2) AS `sel %` 
FROM INFORMATION_SCHEMA.STATISTICS s 
INNER JOIN INFORMATION_SCHEMA.TABLES t ON s.TABLE_SCHEMA = t.TABLE_SCHEMA AND s.TABLE_NAME = t.TABLE_NAME 
INNER JOIN ( 
SELECT TABLE_SCHEMA, TABLE_NAME, INDEX_NAME, MAX(SEQ_IN_INDEX) AS max_columns 
FROM INFORMATION_SCHEMA.STATISTICS 
WHERE TABLE_SCHEMA != 'mysql' GROUP BY TABLE_SCHEMA, TABLE_NAME, INDEX_NAME ) AS s2 ON s.TABLE_SCHEMA = s2.TABLE_SCHEMA AND s.TABLE_NAME = s2.TABLE_NAME AND s.INDEX_NAME = s2.INDEX_NAME 
WHERE t.TABLE_SCHEMA != 'mysql' /* Filter out the mysql system DB */ 
AND t.TABLE_ROWS > 10 /* Only tables with some rows */ 
AND s.CARDINALITY IS NOT NULL /* Need at least one non-NULL value in the field */ 
AND (s.CARDINALITY / IFNULL(t.TABLE_ROWS, 0.01)) < 1.00 /* unique indexes are perfect anyway */ 
ORDER BY `sel %`, s.TABLE_SCHEMA, s.TABLE_NAME /* DESC for best non-unique indexes */ 
LIMIT 10; 