【翻译】查找和调优MySQL慢查询_MySQL

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

explain low_query

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：

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 sINNER JOIN INFORMATION_SCHEMA.TABLES t ON s.TABLE_SCHEMA = t.TABLE_SCHEMA AND s.TABLE_NAME = t.TABLE_NAMEINNER JOIN (SELECT TABLE_SCHEMA, TABLE_NAME, INDEX_NAME, MAX(SEQ_IN_INDEX) AS max_columnsFROM INFORMATION_SCHEMA.STATISTICSWHERE 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_NAMEWHERE 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;