Mysql实例MySQL慢查询查找和调优测试
发布时间:2020-12-12 02:53:31 所属栏目:MySql教程 来源:网络整理
导读:《Mysql实例MySQL慢查询查找和调优测试》要点: 本文介绍了Mysql实例MySQL慢查询查找和调优测试,希望对您有用。如果有疑问,可以联系我们。 编辑 my.cnf或者my.ini文件,去除下面这几行代码的注释: 代码如下: log_slow_queries = /var/log/mysql/mysql-slow
《Mysql实例MySQL慢查询查找和调优测试》要点: 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: 代码如下: explain low_query ? 你将看到下面的结果: +----+-------------+---------------------+------+---------------+------+---------+------+------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+---------------------+------+---------------+------+---------+------+------+-------------+ | 1 | SIMPLE | some_table | ALL | NULL | NULL | NULL | NULL | 166 | Using where | +----+-------------+---------------------+------+---------------+------+---------+------+------+-------------+ 注意上面的rows和key列.rows显示该查询影响了多少行记录,我们不想让这个值太大.key显示用了哪个索引,为NULL时表示查询未用任何索引. 如果想让查询更快,你或许需要为某些列增加索引: CREATE INDEX myapp_mytable_myfield_idx on myapp_mytable(myfield); 除了配置mysql配置文件来实现记录慢查询外,还有下面的方法可以记录慢查询: 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,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; 《Mysql实例MySQL慢查询查找和调优测试》是否对您有启发,欢迎查看更多与《Mysql实例MySQL慢查询查找和调优测试》相关教程,学精学透。编程之家PHP学院为您提供精彩教程。 (编辑:李大同) 【声明】本站内容均来自网络,其相关言论仅代表作者个人观点,不代表本站立场。若无意侵犯到您的权利,请及时与联系站长删除相关内容! |