mysql优化之performance_schema定位mysql问题_select * fron performance schema.events statements-优快云博客

博客总结了MySQL优化常见问题的定位语句。介绍了performance_schema表数据存储特性，服务器重启数据会丢失。还给出多类SQL执行情况、表的物理和逻辑IO、索引使用、等待事件消耗时间等方面的查询语句，以及剖析某条SQL执行情况的相关语句。

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总结了一些mysql优化常见的问题定位语句：

performance_schema的表中的数据不会持久化存储在磁盘中，而是保存在内存中，一旦服务器重启，这些数据会丢失（包括配置表在内的整个performance_schema下的所有数据）

--1、哪类的SQL执行最多？
SELECT DIGEST_TEXT,COUNT_STAR,FIRST_SEEN,LAST_SEEN FROM `performance_schema`.events_statements_summary_by_digest ORDER BY COUNT_STAR DESC
--2、哪类SQL的平均响应时间最多？
SELECT DIGEST_TEXT,AVG_TIMER_WAIT FROM `performance_schema`.events_statements_summary_by_digest ORDER BY COUNT_STAR DESC
--3、哪类SQL排序记录数最多？
SELECT DIGEST_TEXT,SUM_SORT_ROWS FROM `performance_schema`.events_statements_summary_by_digest ORDER BY COUNT_STAR DESC
--4、哪类SQL扫描记录数最多？
SELECT DIGEST_TEXT,SUM_ROWS_EXAMINED FROM `performance_schema`.events_statements_summary_by_digest ORDER BY COUNT_STAR DESC
--5、哪类SQL使用临时表最多？
SELECT DIGEST_TEXT,SUM_CREATED_TMP_TABLES,SUM_CREATED_TMP_DISK_TABLES FROM `performance_schema`.events_statements_summary_by_digest ORDER BY COUNT_STAR DESC
--6、哪类SQL返回结果集最多？
SELECT DIGEST_TEXT,SUM_ROWS_SENT FROM `performance_schema`.events_statements_summary_by_digest ORDER BY COUNT_STAR DESC
--7、哪个表物理IO最多？
SELECT file_name,event_name,SUM_NUMBER_OF_BYTES_READ,SUM_NUMBER_OF_BYTES_WRITE FROM `performance_schema`.file_summary_by_instance ORDER BY SUM_NUMBER_OF_BYTES_READ + SUM_NUMBER_OF_BYTES_WRITE DESC
--8、哪个表逻辑IO最多？
SELECT object_name,COUNT_READ,COUNT_WRITE,COUNT_FETCH,SUM_TIMER_WAIT FROM `performance_schema`.table_io_waits_summary_by_table ORDER BY sum_timer_wait DESC
--9、哪个索引访问最多？
SELECT OBJECT_NAME,INDEX_NAME,COUNT_FETCH,COUNT_INSERT,COUNT_UPDATE,COUNT_DELETE FROM `performance_schema`.table_io_waits_summary_by_index_usage ORDER BY SUM_TIMER_WAIT DESC
--10、哪个索引从来没有用过？
SELECT OBJECT_SCHEMA,OBJECT_NAME,INDEX_NAME FROM `performance_schema`.table_io_waits_summary_by_index_usage WHERE INDEX_NAME IS NOT NULL AND COUNT_STAR = 0 AND OBJECT_SCHEMA <> 'mysql' ORDER BY OBJECT_SCHEMA,OBJECT_NAME;
--11、哪个等待事件消耗时间最多？
SELECT EVENT_NAME,COUNT_STAR,SUM_TIMER_WAIT,AVG_TIMER_WAIT FROM `performance_schema`.events_waits_summary_global_by_event_name WHERE event_name != 'idle' ORDER BY SUM_TIMER_WAIT DESC
--12-1、剖析某条SQL的执行情况，包括statement信息，stege信息，wait信息
SELECT EVENT_ID,sql_text FROM `performance_schema`.events_statements_history WHERE sql_text LIKE '%count(*)%';
--12-2、查看每个阶段的时间消耗
SELECT event_id,EVENT_NAME,SOURCE,TIMER_END - TIMER_START FROM `performance_schema`.events_stages_history_long WHERE NESTING_EVENT_ID = 1553;
--12-3、查看每个阶段的锁等待情况
SELECT event_id,event_name,source,timer_wait,object_name,index_name,operation,nesting_event_id FROM `performance_schema`.events_waits_history_long WHERE nesting_event_id = 1553;
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