一、简介
performance schema 是运行在较低级别的用于监控MySQL运行过程中的资源消耗、等待等情况的功能特性。
特点如下:
1.提供了一种在数据库运行时实时检查server的内部执行情况的方法。其中的表使用performance_schema存储引擎,主要关注数据库运行过程中的
性能相关的数据,而information_schema主要关注server运行过程中的元数据信息
2. 通过监视server的事件来实现监视其内部运行情况。"事件"指MySQL某些活动中所做的事情,对应的时间、资源消耗,活动执行次数等,利用这些
信息来判断相关资源消耗在了哪里。
3.收集的事件数据只记录在本地performance_schema库的表中,这些表中数据发生变化时不会被写入binlog,也不会被复制到其他server。可以
使用SQL语句查询、更新这些表(配置表的更改会立即生效,这会影响数据收集)。
4. performance_schema的表中的数据不会持久化到磁盘,而是保存在内存中,一旦服务器重启,这些数据会丢失。
5. 对于MySQL支持的所有平台,事件监控功能都可用,但不同平台中用于统计事件时间开销的计时器类型可能会有差异。
实现机制遵循以下设计目标:
1. 启用后会持续进行监测,但开销很小,不会导致server行为(线程调度机制、执行计划等)变化,更不会导致server不可用。即使对某事件执行
监测失败,也不会影响server正常运行。
2.如果在开始收集事件数据时正好有其他线程在查询这些事件信息,查询会优先于事件数据收集,因为事件数据的收集是一个持续不断的过程,而查询
这些事件数据仅仅只是在需要查看的时候才进行,也可能某些事件数据永远都不会被查询。
3.如果需要,可以很容易地添加新的instruments监测点;如果instruments的代码发生了变更,旧的代码还可以继续工作。
二、使用查询
1. 检查当前版本是否支持performance_schema
performance_schema被视为存储引擎。如果支持,则应该在INFORMATION_SCHEMA.ENGINES表或SHOW ENGINES语句的输出中都可以看到它的SUPPORT值为YES。
2、查看该特性是否使用
该参数为只读参数,要显式启用或关闭时,需要在my.cnf中配置参数performance_schema=ON|OFF
[mysqld]
performance_schema = ON
三、performance_schema下的表
1、使用该引擎的这些表的分类
可以通过从INFORMATION_SCHEMA.tables表查询有哪些performance_schema引擎的表:
SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLES \
WHERE TABLE_SCHEMA ='performance_schema' and engine='performance_schema';
也可以直接在performance_schema库下使用show tables语句:
use performance_schema
show tables;
或者
show tables from performance_schema;
通过查询,在mysql 8.0版本中,共有110个表。这些表根据监测维度不同,我们将其分为:
1)语句事件记录表
show tables like 'events_statement%';
+----------------------------------------------------+
| Tables_in_performance_schema (events_statement%) |
+----------------------------------------------------+
| events_statements_current | //当前语句事件表
| events_statements_histogram_by_digest | //历史语句事件表
| events_statements_histogram_global |
| events_statements_history |
| events_statements_history_long | //长语句历史事件表
| events_statements_summary_by_account_by_event_name | //聚合后的摘要表
| events_statements_summary_by_digest |
| events_statements_summary_by_host_by_event_name |
| events_statements_summary_by_program |
| events_statements_summary_by_thread_by_event_name |
| events_statements_summary_by_user_by_event_name |
| events_statements_summary_global_by_event_name |
+----------------------------------------------------+
2)等待时间记录表
mysql> show tables like 'events_wait%';
+-----------------------------------------------+
| Tables_in_performance_schema (events_wait%) |
+-----------------------------------------------+
| events_waits_current |
| events_waits_history |
| events_waits_history_long |
| events_waits_summary_by_account_by_event_name |
| events_waits_summary_by_host_by_event_name |
| events_waits_summary_by_instance |
| events_waits_summary_by_thread_by_event_name |
| events_waits_summary_by_user_by_event_name |
| events_waits_summary_global_by_event_name |
+-----------------------------------------------+
3)阶段事件记录表
mysql> show tables like 'events_stage%';
+------------------------------------------------+
| Tables_in_performance_schema (events_stage%) |
+------------------------------------------------+
| events_stages_current |
| events_stages_history |
| events_stages_history_long |
| events_stages_summary_by_account_by_event_name |
| events_stages_summary_by_host_by_event_name |
| events_stages_summary_by_thread_by_event_name |
| events_stages_summary_by_user_by_event_name |
| events_stages_summary_global_by_event_name |
+------------------------------------------------+
4)事务事件记录表
mysql> show tables like 'events_transaction%';
+------------------------------------------------------+
| Tables_in_performance_schema (events_transaction%) |
+------------------------------------------------------+
| events_transactions_current |
| events_transactions_history |
| events_transactions_history_long |
| events_transactions_summary_by_account_by_event_name |
| events_transactions_summary_by_host_by_event_name |
| events_transactions_summary_by_thread_by_event_name |
| events_transactions_summary_by_user_by_event_name |
| events_transactions_summary_global_by_event_name |
+------------------------------------------------------+
5)监控文件系统层调用的表
mysql> show tables like '%file%';
+---------------------------------------+
| Tables_in_performance_schema (%file%) |
+---------------------------------------+
| file_instances |
| file_summary_by_event_name |
| file_summary_by_instance |
+---------------------------------------+
6)监视内存使用的表
mysql> show tables like '%memory%';
+-----------------------------------------+
| Tables_in_performance_schema (%memory%) |
+-----------------------------------------+
| memory_summary_by_account_by_event_name |
| memory_summary_by_host_by_event_name |
| memory_summary_by_thread_by_event_name |
| memory_summary_by_user_by_event_name |
| memory_summary_global_by_event_name |
+-----------------------------------------+
7)动态对performance_schema进行配置的配置表
mysql> show tables like '%setup%';
+----------------------------------------+
| Tables_in_performance_schema (%setup%) |
+----------------------------------------+
| setup_actors |
| setup_consumers |
| setup_instruments |
| setup_objects |
| setup_threads |
+----------------------------------------+
2、两个基本概念
● instruments:生产者,用于采集MySQL中各种操作产生的事件信息,对应配置表中的配置项,我们可以称之为事件采集配置项。以下提及的生产者均统称为instruments。
● consumers:消费者,对应的消费者表用于存储来自instruments采集的数据,对应配置表中的配置项,我们可以称之为消费存储配置项。以下提及的消费者均统称为consumers。
查询性能表进行进行分析
基本了解了表的相关信息之后,可以通过这些表进行实际的查询操作来进行实际的分析。
1、哪类的SQL执行最多?
mysql> 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?
mysql> 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?
mysql> 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?
mysql> 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?
mysql> 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?
mysql> 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?
mysql> 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?
mysql> 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?
mysql> 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?
mysql> 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?
mysql> 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、剖析某条SQL的执行情况,包括statement信息,stege信息,wait信息
mysql> SELECT EVENT_ID,sql_text FROM events_statements_history WHERE sql_text LIKE '%count(*)%';
13、查看每个阶段的时间消耗
mysql> SELECT event_id,EVENT_NAME,SOURCE,TIMER_END - TIMER_START FROM events_stages_history_long WHERE
NESTING_EVENT_ID = 1553;
14、查看每个阶段的锁等待情况
mysql> SELECT event_id,event_name,source,timer_wait,object_name,index_name,operation,nesting_event_id FROM
events_waits_history_long;