性能监控
show profiles
show profile默认是关闭的，并且开启后只存活于当前会话，也就说每次使用前都需要开启
使用前开启：set profiling=1
再使用show profiles所有语句以及对应的执行时间
查看某条语句具体执行的所有信息：show profile all for query query_id
all：所有信息(cpu,block…)
show processlist
查看数据库的连接信息
Performance schema
默认是开启的 mysql系统会创建名为performance_schema的数据库，用于监控MySQL server在一个较低级别的运行过程中的资源消耗、资源等待等情况
其中包含87张表，表中的数据不会存入磁盘而是在内存中存储，这些表大概可以分为以下几类：
show tables like '%statement%';
语句事件记录表，这些表记录了语句事件信息，当前语句事件表events_statements_current、历史语句事件表events_statements_history和长语句历史事件表events_statements_history_long、以及聚合后的摘要表summary，其中，summary表还可以根据帐号(account)，主机(host)，程序(program)，线程(thread)，用户(user)和全局(global)再进行细分)
show tables like '%wait%';
等待事件记录表，与语句事件类型的相关记录表类似：
show tables like '%stage%';
–阶段事件记录表，记录语句执行的阶段事件的表
show tables like '%transaction%';
–事务事件记录表，记录事务相关的事件的表
show tables like '%file%';
–监控文件系统层调用的表
show tables like '%memory%';
–监视内存使用的表
show tables like '%setup%';
–动态对performance_schema进行配置的配置表
实践
–1、哪类的SQL执行最多？
SELECT DIGEST_TEXT,COUNT_STAR,FIRST_SEEN,LAST_SEEN FROM 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 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 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 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 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 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 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 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 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 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 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 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 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 events_waits_history_longWHERE nesting_event_id = 1553;
