怎么理解MySQL5.6中的PERFORMANCE_SCHEM

發(fā)布時間：2021-11-08 11:39:08 來源：億速云閱讀：151 作者：iii 欄目：MySQL數(shù)據(jù)庫

本篇內(nèi)容介紹了“怎么理解MySQL5.6中的PERFORMANCE_SCHEM”的有關知識，在實際案例的操作過程中，不少人都會遇到這樣的困境，接下來就讓小編帶領大家學習一下如何處理這些情況吧！希望大家仔細閱讀，能夠學有所成！

通過sql語句找到在經(jīng)歷什么等待事件!

Statement -> stage -> wait的三級結構，通過nesting_event_id進行關聯(lián)，它表示某個事件的父event_id。

比如分析包含count(*)的某條SQL語句，具體如下：(類似于oracle的v$sql, v$sqlstat, v$sqlarea)

SELECT

EVENT_ID,

sql_text

FROM events_statements_history

WHERE sql_text LIKE '%count(*)%';

+----------+--------------------------------------+

| EVENT_ID | sql_text |

+----------+--------------------------------------+

| 1690 | select count(*) from chuck.test_slow |

+----------+--------------------------------------+

a.查看每個階段的時間消耗：(類似于oracle的時間模型V$SYS_TIME_MODEL V$SESS_TIME_MODEL)

SELECT

event_id,

EVENT_NAME,

SOURCE,

TIMER_END - TIMER_START

FROM events_stages_history_long

WHERE NESTING_EVENT_ID = 1690;

+----------+--------------------------------+----------------------+-----------------------+

+----------+--------------------------------+----------------------+-----------------------+

……

| 2647 | stage/sql/Sending data | sql_executor.cc:192 | 7369072089000 |

b.查看某個階段的鎖等待情況 (類似于oracle的v$session_wait)

針對每個stage可能出現(xiàn)的鎖等待，一個stage會對應一個或多個wait，events_waits_history_long這個表容易爆滿[默認閥值10000]。由于select count(*)需要IO(邏輯IO或者物理IO)，所以在stage/sql/Sending data階段會有io等待的統(tǒng)計。通過stage_xxx表的event_id字段與waits_xxx表的nesting_event_id進行關聯(lián)。

SELECT

event_id,

event_name,

source,

timer_wait,

object_name,

index_name,

operation,

nesting_event_id

FROM events_waits_history_long

WHERE nesting_event_id = 2647;

+----------+---------------------------+-----------------+------------+-------------+------------+-----------+------------------+

+----------+---------------------------+-----------------+------------+-------------+------------+-----------+------------------+

https://www.cnblogs.com/zhoujinyi/p/5236705.html

MySQL5.6 PERFORMANCE_SCHEMA 說明

背景：

MySQL 5.5開始新增一個數(shù)據(jù)庫：PERFORMANCE_SCHEMA，主要用于收集數(shù)據(jù)庫服務器性能參數(shù)。并且?guī)炖锉淼拇鎯σ婢鶠镻ERFORMANCE_SCHEMA，而用戶是不能創(chuàng)建存儲引擎為PERFORMANCE_SCHEMA的表。MySQL5.5默認是關閉的，需要手動開啟，在配置文件里添加：

[mysqld]

performance_schema=ON

查看是否開啟：

mysql>show variables like 'performance_schema';

+--------------------+-------+

| Variable_name | Value |

+--------------------+-------+

| performance_schema | ON |

+--------------------+-------+

從MySQL5.6開始，默認打開，本文就從MySQL5.6來說明，在數(shù)據(jù)庫使用當中PERFORMANCE_SCHEMA的一些比較常用的功能。具體的信息可以查看官方文檔。

相關表信息：

一：配置（setup）表：

zjy@performance_schema 10:16:56>show tables like '%setup%';

+----------------------------------------+

| Tables_in_performance_schema (%setup%) |

+----------------------------------------+

| setup_actors |

| setup_consumers |

| setup_instruments |

| setup_objects |

| setup_timers |

+----------------------------------------+

1，setup_actors：配置用戶緯度的監(jiān)控，默認監(jiān)控所有用戶。

zjy@performance_schema 10:19:11>select * from setup_actors;

+------+------+------+

| HOST | USER | ROLE |

+------+------+------+

| % | % | % |

+------+------+------+

2，setup_consumers：配置events的消費者類型，即收集的events寫入到哪些統(tǒng)計表中。

zjy@: performance_schema 10:23:35>select * from setup_consumers;

+--------------------------------+---------+

| NAME | ENABLED |

+--------------------------------+---------+

| events_stages_current | NO |

| events_stages_history | NO |

| events_stages_history_long | NO |

| events_statements_current | YES |

| events_statements_history | NO |

| events_statements_history_long | NO |

| events_waits_current | NO |

| events_waits_history | NO |

| events_waits_history_long | NO |

| global_instrumentation | YES |

| thread_instrumentation | YES |

| statements_digest | YES |

+--------------------------------+---------+

這里需要說明的是需要查看哪個就更新其ENABLED列為YES。如：

zjy@performance_schema 10:25:02>update setup_consumers set ENABLED='YES' where NAME in ('events_stages_current','events_waits_current');

Query OK, 2 rows affected (0.00 sec)

更新完后立即生效，但是服務器重啟之后又會變回默認值，要永久生效需要在配置文件里添加：

[mysqld]

#performance_schema

performance_schema_consumer_events_waits_current=on

performance_schema_consumer_events_stages_current=on

performance_schema_consumer_events_statements_current=on

performance_schema_consumer_events_waits_history=on

performance_schema_consumer_events_stages_history=on

performance_schema_consumer_events_statements_history=on

即在這些表的前面加上：performance_schema_consumer_xxx。表setup_consumers里面的值有個層級關系：

global_instrumentation > thread_instrumentation = statements_digest > events_stages_current = events_statements_current = events_waits_current > events_stages_history = events_statements_history = events_waits_history > events_stages_history_long = events_statements_history_long = events_waits_history_long

只有上一層次的為YES，才會繼續(xù)檢查該本層為YES or NO。global_instrumentation是最高級別consumer，如果它設置為NO，則所有的consumer都會忽略。其中history和history_long存的是current表的歷史記錄條數(shù)，history表記錄了每個線程最近等待的10個事件，而history_long表則記錄了最近所有線程產(chǎn)生的10000個事件，這里的10和10000都是可以配置的。這三個表表結構相同，history和history_long表數(shù)據(jù)都來源于current表。長度通過控制參數(shù)：

zjy@performance_schema 11:10:03>show variables like 'performance_schema%history%size';

+--------------------------------------------------------+-------+

| Variable_name | Value |

+--------------------------------------------------------+-------+

| performance_schema_events_stages_history_long_size | 10000 |

| performance_schema_events_stages_history_size | 10 |

| performance_schema_events_statements_history_long_size | 10000 |

| performance_schema_events_statements_history_size | 10 |

| performance_schema_events_waits_history_long_size | 10000 |

| performance_schema_events_waits_history_size | 10 |

+--------------------------------------------------------+-------+

3，setup_instruments：配置具體的instrument，主要包含4大類：idle、stage/xxx、statement/xxx、wait/xxx：

zjy@performance_schema 10:56:35>select name,count(*) from setup_instruments group by LEFT(name,5);

+---------------------------------+----------+

| name | count(*) |

+---------------------------------+----------+

| idle | 1 |

| stage/sql/After create | 111 |

| statement/sql/select | 179 |

| wait/synch/mutex/sql/PAGE::lock | 296 |

+---------------------------------+----------+

idle表示socket空閑的時間，stage類表示語句的每個執(zhí)行階段的統(tǒng)計，statement類統(tǒng)計語句維度的信息，wait類統(tǒng)計各種等待事件，比如IO，mutux，spin_lock,condition等。

4，setup_objects：配置監(jiān)控對象，默認對mysql，performance_schema和information_schema中的表都不監(jiān)控，而其它DB的所有表都監(jiān)控。

zjy@performance_schema 11:00:18>select * from setup_objects;

+-------------+--------------------+-------------+---------+-------+

+-------------+--------------------+-------------+---------+-------+

| TABLE | mysql | % | NO | NO |

| TABLE | performance_schema | % | NO | NO |

| TABLE | information_schema | % | NO | NO |

| TABLE | % | % | YES | YES |

+-------------+--------------------+-------------+---------+-------+

5，setup_timers：配置每種類型指令的統(tǒng)計時間單位。MICROSECOND表示統(tǒng)計單位是微妙，CYCLE表示統(tǒng)計單位是時鐘周期，時間度量與CPU的主頻有關，NANOSECOND表示統(tǒng)計單位是納秒。但無論采用哪種度量單位，最終統(tǒng)計表中統(tǒng)計的時間都會裝換到皮秒。（1秒＝1000000000000皮秒）

zjy@performance_schema 11:05:12>select * from setup_timers;

+-----------+-------------+

| NAME | TIMER_NAME |

+-----------+-------------+

| idle | MICROSECOND |

| wait | CYCLE |

| stage | NANOSECOND |

| statement | NANOSECOND |

+-----------+-------------+

二：instance表

1，cond_instances：條件等待對象實例

表中記錄了系統(tǒng)中使用的條件變量的對象，OBJECT_INSTANCE_BEGIN為對象的內(nèi)存地址。

2，file_instances：文件實例

表中記錄了系統(tǒng)中打開了文件的對象，包括ibdata文件，redo文件，binlog文件，用戶的表文件等，open_count顯示當前文件打開的數(shù)目，如果重來沒有打開過，不會出現(xiàn)在表中。

zjy@performance_schema 11:20:04>select * from file_instances limit 2,5;

+---------------------------------+--------------------------------------+------------+

| FILE_NAME | EVENT_NAME | OPEN_COUNT |

+---------------------------------+--------------------------------------+------------+

| /var/lib/mysql/mysql/plugin.frm | wait/io/file/sql/FRM | |

| /var/lib/mysql/mysql/plugin.MYI | wait/io/file/myisam/kfile | 1 |

| /var/lib/mysql/mysql/plugin.MYD | wait/io/file/myisam/dfile | 1 |

| /var/lib/mysql/ibdata1 | wait/io/file/innodb/innodb_data_file | 2 |

| /var/lib/mysql/ib_logfile0 | wait/io/file/innodb/innodb_log_file | 2 |

+---------------------------------+--------------------------------------+------------+

3，mutex_instances：互斥同步對象實例

表中記錄了系統(tǒng)中使用互斥量對象的所有記錄，其中name為：wait/synch/mutex/*。LOCKED_BY_THREAD_ID顯示哪個線程正持有mutex，若沒有線程持有，則為NULL。

4，rwlock_instances：讀寫鎖同步對象實例

表中記錄了系統(tǒng)中使用讀寫鎖對象的所有記錄，其中name為 wait/synch/rwlock/*。WRITE_LOCKED_BY_THREAD_ID為正在持有該對象的thread_id，若沒有線程持有，則為NULL。READ_LOCKED_BY_COUNT為記錄了同時有多少個讀者持有讀鎖。（通過 events_waits_current 表可以知道，哪個線程在等待鎖；通過rwlock_instances知道哪個線程持有鎖。rwlock_instances的缺陷是，只能記錄持有寫鎖的線程，對于讀鎖則無能為力）。

5，socket_instances：活躍會話對象實例
表中記錄了thread_id,socket_id,ip和port，其它表可以通過thread_id與socket_instance進行關聯(lián)，獲取IP-PORT信息，能夠與應用對接起來。
event_name主要包含3類：
wait/io/socket/sql/server_unix_socket，服務端unix監(jiān)聽socket
wait/io/socket/sql/server_tcpip_socket，服務端tcp監(jiān)聽socket
wait/io/socket/sql/client_connection，客戶端socket

三：Wait表

1，events_waits_current：記錄了當前線程等待的事件

2，events_waits_history：記錄了每個線程最近等待的10個事件

3，events_waits_history_long：記錄了最近所有線程產(chǎn)生的10000個事件

表結構定義如下：

CREATE TABLE `events_waits_current` (

`THREAD_ID` bigint(20) unsigned NOT NULL COMMENT '線程ID',

`EVENT_ID` bigint(20) unsigned NOT NULL COMMENT '當前線程的事件ID，和THREAD_ID確定唯一',

`END_EVENT_ID` bigint(20) unsigned DEFAULT NULL COMMENT '當事件開始時，這一列被設置為NULL。當事件結束時，再更新為當前的事件ID',

`EVENT_NAME` varchar(128) NOT NULL COMMENT '事件名稱',

`SOURCE` varchar(64) DEFAULT NULL COMMENT '該事件產(chǎn)生時的源碼文件',

`TIMER_START` bigint(20) unsigned DEFAULT NULL COMMENT '事件開始時間（皮秒）',

`TIMER_END` bigint(20) unsigned DEFAULT NULL COMMENT '事件結束結束時間（皮秒）',

`TIMER_WAIT` bigint(20) unsigned DEFAULT NULL COMMENT '事件等待時間（皮秒）',

`SPINS` int(10) unsigned DEFAULT NULL COMMENT '',

`OBJECT_SCHEMA` varchar(64) DEFAULT NULL COMMENT '庫名',

`OBJECT_NAME` varchar(512) DEFAULT NULL COMMENT '文件名、表名、IP:SOCK值',

`OBJECT_TYPE` varchar(64) DEFAULT NULL COMMENT 'FILE、TABLE、TEMPORARY TABLE',

`INDEX_NAME` varchar(64) DEFAULT NULL COMMENT '索引名',

`OBJECT_INSTANCE_BEGIN` bigint(20) unsigned NOT NULL COMMENT '內(nèi)存地址',

`NESTING_EVENT_ID` bigint(20) unsigned DEFAULT NULL COMMENT '該事件對應的父事件ID',

`NESTING_EVENT_TYPE` enum('STATEMENT','STAGE','WAIT') DEFAULT NULL COMMENT '父事件類型(STATEMENT, STAGE, WAIT)',

`OPERATION` varchar(32) NOT NULL COMMENT '操作類型（lock, read, write）',

`NUMBER_OF_BYTES` bigint(20) DEFAULT NULL COMMENT '',

`FLAGS` int(10) unsigned DEFAULT NULL COMMENT '標記'

) ENGINE=PERFORMANCE_SCHEMA DEFAULT CHARSET=utf8

四：Stage 表

1，events_stages_current：記錄了當前線程所處的執(zhí)行階段

2，events_stages_history：記錄了當前線程所處的執(zhí)行階段10條歷史記錄

3，events_stages_history_long：記錄了當前線程所處的執(zhí)行階段10000條歷史記錄

表結構定義如下：

CREATE TABLE `events_stages_current` (

`THREAD_ID` bigint(20) unsigned NOT NULL COMMENT '線程ID',

`EVENT_ID` bigint(20) unsigned NOT NULL COMMENT '事件ID',

`END_EVENT_ID` bigint(20) unsigned DEFAULT NULL COMMENT '結束事件ID',

`EVENT_NAME` varchar(128) NOT NULL COMMENT '事件名稱',

`SOURCE` varchar(64) DEFAULT NULL COMMENT '源碼位置',

`TIMER_START` bigint(20) unsigned DEFAULT NULL COMMENT '事件開始時間（皮秒）',

`TIMER_END` bigint(20) unsigned DEFAULT NULL COMMENT '事件結束結束時間（皮秒）',

`TIMER_WAIT` bigint(20) unsigned DEFAULT NULL COMMENT '事件等待時間（皮秒）',

`NESTING_EVENT_ID` bigint(20) unsigned DEFAULT NULL COMMENT '該事件對應的父事件ID',

`NESTING_EVENT_TYPE` enum('STATEMENT','STAGE','WAIT') DEFAULT NULL COMMENT '父事件類型(STATEMENT, STAGE, WAIT)'

) ENGINE=PERFORMANCE_SCHEMA DEFAULT CHARSET=utf8

五：Statement 表

1，events_statements_current：通過 thread_id+event_id可以唯一確定一條記錄。Statments表只記錄最頂層的請求，SQL語句或是COMMAND，每條語句一行。event_name形式為statement/sql/*，或statement/com/*

2，events_statements_history

3，events_statements_history_long

表結構定義如下：

CREATE TABLE `events_statements_current` (

`THREAD_ID` bigint(20) unsigned NOT NULL COMMENT '線程ID',

`EVENT_ID` bigint(20) unsigned NOT NULL COMMENT '事件ID',

`END_EVENT_ID` bigint(20) unsigned DEFAULT NULL COMMENT '結束事件ID',

`EVENT_NAME` varchar(128) NOT NULL COMMENT '事件名稱',

`SOURCE` varchar(64) DEFAULT NULL COMMENT '源碼位置',

`TIMER_START` bigint(20) unsigned DEFAULT NULL COMMENT '事件開始時間（皮秒）',

`TIMER_END` bigint(20) unsigned DEFAULT NULL COMMENT '事件結束結束時間（皮秒）',

`TIMER_WAIT` bigint(20) unsigned DEFAULT NULL COMMENT '事件等待時間（皮秒）',

`LOCK_TIME` bigint(20) unsigned NOT NULL COMMENT '鎖時間',

`SQL_TEXT` longtext COMMENT '記錄SQL語句',

`DIGEST` varchar(32) DEFAULT NULL COMMENT '對SQL_TEXT做MD5產(chǎn)生的32位字符串',

`DIGEST_TEXT` longtext COMMENT '將語句中值部分用問號代替，用于SQL語句歸類',

`CURRENT_SCHEMA` varchar(64) DEFAULT NULL COMMENT '默認的數(shù)據(jù)庫名',

`OBJECT_TYPE` varchar(64) DEFAULT NULL COMMENT '保留字段',

`OBJECT_SCHEMA` varchar(64) DEFAULT NULL COMMENT '保留字段',

`OBJECT_NAME` varchar(64) DEFAULT NULL COMMENT '保留字段',

`OBJECT_INSTANCE_BEGIN` bigint(20) unsigned DEFAULT NULL COMMENT '內(nèi)存地址',

`MYSQL_ERRNO` int(11) DEFAULT NULL COMMENT '',

`RETURNED_SQLSTATE` varchar(5) DEFAULT NULL COMMENT '',

`MESSAGE_TEXT` varchar(128) DEFAULT NULL COMMENT '信息',

`ERRORS` bigint(20) unsigned NOT NULL COMMENT '錯誤數(shù)目',

`WARNINGS` bigint(20) unsigned NOT NULL COMMENT '警告數(shù)目',

`ROWS_AFFECTED` bigint(20) unsigned NOT NULL COMMENT '影響的數(shù)目',

`ROWS_SENT` bigint(20) unsigned NOT NULL COMMENT '返回的記錄數(shù)',

`ROWS_EXAMINED` bigint(20) unsigned NOT NULL COMMENT '讀取掃描的記錄數(shù)目',

`CREATED_TMP_DISK_TABLES` bigint(20) unsigned NOT NULL COMMENT '創(chuàng)建磁盤臨時表數(shù)目',

`CREATED_TMP_TABLES` bigint(20) unsigned NOT NULL COMMENT '創(chuàng)建臨時表數(shù)目',

`SELECT_FULL_JOIN` bigint(20) unsigned NOT NULL COMMENT 'join時，第一個表為全表掃描的數(shù)目',

`SELECT_FULL_RANGE_JOIN` bigint(20) unsigned NOT NULL COMMENT '引用表采用range方式掃描的數(shù)目',

`SELECT_RANGE` bigint(20) unsigned NOT NULL COMMENT 'join時，第一個表采用range方式掃描的數(shù)目',

`SELECT_RANGE_CHECK` bigint(20) unsigned NOT NULL COMMENT '',

`SELECT_SCAN` bigint(20) unsigned NOT NULL COMMENT 'join時，第一個表位全表掃描的數(shù)目',

`SORT_MERGE_PASSES` bigint(20) unsigned NOT NULL COMMENT '',

`SORT_RANGE` bigint(20) unsigned NOT NULL COMMENT '范圍排序數(shù)目',

`SORT_ROWS` bigint(20) unsigned NOT NULL COMMENT '排序的記錄數(shù)目',

`SORT_SCAN` bigint(20) unsigned NOT NULL COMMENT '全表排序數(shù)目',

`NO_INDEX_USED` bigint(20) unsigned NOT NULL COMMENT '沒有使用索引數(shù)目',

`NO_GOOD_INDEX_USED` bigint(20) unsigned NOT NULL COMMENT '',

`NESTING_EVENT_ID` bigint(20) unsigned DEFAULT NULL COMMENT '該事件對應的父事件ID',

`NESTING_EVENT_TYPE` enum('STATEMENT','STAGE','WAIT') DEFAULT NULL COMMENT '父事件類型(STATEMENT, STAGE, WAIT)'

) ENGINE=PERFORMANCE_SCHEMA DEFAULT CHARSET=utf8

六：Connection 表

1，users：記錄用戶連接數(shù)信息

2，hosts：記錄了主機連接數(shù)信息

3，accounts：記錄了用戶主機連接數(shù)信息

zjy@performance_schema 12:03:27>select * from users;

+------------------+---------------------+-------------------+

| USER | CURRENT_CONNECTIONS | TOTAL_CONNECTIONS |

+------------------+---------------------+-------------------+

| debian-sys-maint | | 36 |

| zjy | 1 | 22285 |

| dchat_php | | 37864 |

| dxyslave | 2 | 9 |

| nagios | | 10770 |

| dchat_data | 140 | 2233023 |

| NULL | | 15866 |

| dchat_api | 160 | 2754212 |

| mha_data | 1 | 36 |

| backup | | 15 |

| cacti | | 4312 |

| kol | 10 | 172414 |

+------------------+---------------------+-------------------+

12 rows in set (0.00 sec)

zjy@performance_schema 12:03:34>select * from hosts;

+-----------------+---------------------+-------------------+

| HOST | CURRENT_CONNECTIONS | TOTAL_CONNECTIONS |

+-----------------+---------------------+-------------------+

| 192.168.100.218 | 150 | 2499422 |

| 192.168.100.240 | 10 | 172429 |

| 192.168.100.139 | | 698 |

| 192.168.100.21 | | 2 |

| 192.168.100.220 | 150 | 2526136 |

| 192.168.100.25 | 1 | 7 |

| NULL | | 15867 |

| 192.168.100.241 | | 21558 |

| 192.168.100.191 | 1 | 34 |

| localhost | | 10807 |

| 192.168.100.118 | 1 | 2 |

| 192.168.100.251 | | 4312 |

| 192.168.100.23 | 1 | 31 |

| 192.168.100.193 | | 15 |

+-----------------+---------------------+-------------------+

14 rows in set (0.01 sec)

zjy@performance_schema 12:05:21>select * from accounts;

+------------------+-----------------+---------------------+-------------------+

+------------------+-----------------+---------------------+-------------------+

| cacti | 192.168.100.251 | | 4313 |

| backup | 192.168.100.193 | | 15 |

| dchat_api | 192.168.100.220 | 80 | 1382585 |

| dchat_php | 192.168.100.220 | | 20292 |

| zjy | 192.168.100.139 | | 698 |

| zjy | 192.168.100.241 | | 21558 |

| mha_data | 192.168.100.191 | 1 | 34 |

| dxyslave | 192.168.100.118 | 1 | 2 |

| kol | 192.168.100.240 | 10 | 172431 |

| dxyslave | 192.168.100.25 | 1 | 7 |

| dchat_data | 192.168.100.218 | 70 | 1109974 |

| zjy | 192.168.100.23 | 1 | 31 |

| dchat_php | 192.168.100.218 | | 17572 |

| dchat_data | 192.168.100.220 | 70 | 1123306 |

| mha_data | 192.168.100.21 | | 2 |

| dchat_api | 192.168.100.218 | 80 | 1371918 |

+------------------+-----------------+---------------------+-------------------+

View Code

七：Summary 表： Summary表聚集了各個維度的統(tǒng)計信息包括表維度，索引維度，會話維度，語句維度和鎖維度的統(tǒng)計信息

1，events_waits_summary_global_by_event_name：按等待事件類型聚合，每個事件一條記錄

CREATE TABLE `events_waits_summary_global_by_event_name` (

`EVENT_NAME` varchar(128) NOT NULL COMMENT '事件名稱',

`COUNT_STAR` bigint(20) unsigned NOT NULL COMMENT '事件計數(shù)',

`SUM_TIMER_WAIT` bigint(20) unsigned NOT NULL COMMENT '總的等待時間',

`MIN_TIMER_WAIT` bigint(20) unsigned NOT NULL COMMENT '最小等待時間',

`AVG_TIMER_WAIT` bigint(20) unsigned NOT NULL COMMENT '平均等待時間',

`MAX_TIMER_WAIT` bigint(20) unsigned NOT NULL COMMENT '最大等待時間'

) ENGINE=PERFORMANCE_SCHEMA DEFAULT CHARSET=utf8

2，events_waits_summary_by_instance：按等待事件對象聚合，同一種等待事件，可能有多個實例，每個實例有不同的內(nèi)存地址，因此
event_name+object_instance_begin唯一確定一條記錄。

CREATE TABLE `events_waits_summary_by_instance` (

`EVENT_NAME` varchar(128) NOT NULL COMMENT '事件名稱',

`OBJECT_INSTANCE_BEGIN` bigint(20) unsigned NOT NULL COMMENT '內(nèi)存地址',

`COUNT_STAR` bigint(20) unsigned NOT NULL COMMENT '事件計數(shù)',

`SUM_TIMER_WAIT` bigint(20) unsigned NOT NULL COMMENT '總的等待時間',

`MIN_TIMER_WAIT` bigint(20) unsigned NOT NULL COMMENT '最小等待時間',

`AVG_TIMER_WAIT` bigint(20) unsigned NOT NULL COMMENT '平均等待時間',

`MAX_TIMER_WAIT` bigint(20) unsigned NOT NULL COMMENT '最大等待時間'

) ENGINE=PERFORMANCE_SCHEMA DEFAULT CHARSET=utf8

3，events_waits_summary_by_thread_by_event_name：按每個線程和事件來統(tǒng)計，thread_id+event_name唯一確定一條記錄。

CREATE TABLE `events_waits_summary_by_thread_by_event_name` (

`THREAD_ID` bigint(20) unsigned NOT NULL COMMENT '線程ID',

`EVENT_NAME` varchar(128) NOT NULL COMMENT '事件名稱',

`COUNT_STAR` bigint(20) unsigned NOT NULL COMMENT '事件計數(shù)',

`SUM_TIMER_WAIT` bigint(20) unsigned NOT NULL COMMENT '總的等待時間',

`MIN_TIMER_WAIT` bigint(20) unsigned NOT NULL COMMENT '最小等待時間',

`AVG_TIMER_WAIT` bigint(20) unsigned NOT NULL COMMENT '平均等待時間',

`MAX_TIMER_WAIT` bigint(20) unsigned NOT NULL COMMENT '最大等待時間'

) ENGINE=PERFORMANCE_SCHEMA DEFAULT CHARSET=utf8

4，events_stages_summary_global_by_event_name：按事件階段類型聚合，每個事件一條記錄，表結構同上。

5，events_stages_summary_by_thread_by_event_name：按每個線程和事件來階段統(tǒng)計，表結構同上。

6，events_statements_summary_by_digest：按照事件的語句進行聚合。

CREATE TABLE `events_statements_summary_by_digest` (

`SCHEMA_NAME` varchar(64) DEFAULT NULL COMMENT '庫名',

`DIGEST` varchar(32) DEFAULT NULL COMMENT '對SQL_TEXT做MD5產(chǎn)生的32位字符串。如果為consumer表中沒有打開statement_digest選項，則為NULL',

`DIGEST_TEXT` longtext COMMENT '將語句中值部分用問號代替，用于SQL語句歸類。如果為consumer表中沒有打開statement_digest選項，則為NULL。',

`COUNT_STAR` bigint(20) unsigned NOT NULL COMMENT '事件計數(shù)',

`SUM_TIMER_WAIT` bigint(20) unsigned NOT NULL COMMENT '總的等待時間',

`MIN_TIMER_WAIT` bigint(20) unsigned NOT NULL COMMENT '最小等待時間',

`AVG_TIMER_WAIT` bigint(20) unsigned NOT NULL COMMENT '平均等待時間',

`MAX_TIMER_WAIT` bigint(20) unsigned NOT NULL COMMENT '最大等待時間',

`SUM_LOCK_TIME` bigint(20) unsigned NOT NULL COMMENT '鎖時間總時長',

`SUM_ERRORS` bigint(20) unsigned NOT NULL COMMENT '錯誤數(shù)的總',

`SUM_WARNINGS` bigint(20) unsigned NOT NULL COMMENT '警告的總數(shù)',

`SUM_ROWS_AFFECTED` bigint(20) unsigned NOT NULL COMMENT '影響的總數(shù)目',

`SUM_ROWS_SENT` bigint(20) unsigned NOT NULL COMMENT '返回總數(shù)目',

`SUM_ROWS_EXAMINED` bigint(20) unsigned NOT NULL COMMENT '總的掃描的數(shù)目',

`SUM_CREATED_TMP_DISK_TABLES` bigint(20) unsigned NOT NULL COMMENT '創(chuàng)建磁盤臨時表的總數(shù)目',

`SUM_CREATED_TMP_TABLES` bigint(20) unsigned NOT NULL COMMENT '創(chuàng)建臨時表的總數(shù)目',

`SUM_SELECT_FULL_JOIN` bigint(20) unsigned NOT NULL COMMENT '第一個表全表掃描的總數(shù)目',

`SUM_SELECT_FULL_RANGE_JOIN` bigint(20) unsigned NOT NULL COMMENT '總的采用range方式掃描的數(shù)目',

`SUM_SELECT_RANGE` bigint(20) unsigned NOT NULL COMMENT '第一個表采用range方式掃描的總數(shù)目',

`SUM_SELECT_RANGE_CHECK` bigint(20) unsigned NOT NULL COMMENT '',

`SUM_SELECT_SCAN` bigint(20) unsigned NOT NULL COMMENT '第一個表位全表掃描的總數(shù)目',

`SUM_SORT_MERGE_PASSES` bigint(20) unsigned NOT NULL COMMENT '',

`SUM_SORT_RANGE` bigint(20) unsigned NOT NULL COMMENT '范圍排序總數(shù)',

`SUM_SORT_ROWS` bigint(20) unsigned NOT NULL COMMENT '排序的記錄總數(shù)目',

`SUM_SORT_SCAN` bigint(20) unsigned NOT NULL COMMENT '第一個表排序掃描總數(shù)目',

`SUM_NO_INDEX_USED` bigint(20) unsigned NOT NULL COMMENT '沒有使用索引總數(shù)',

`SUM_NO_GOOD_INDEX_USED` bigint(20) unsigned NOT NULL COMMENT '',

`FIRST_SEEN` timestamp NOT NULL DEFAULT '0000-00-00 00:00:00' COMMENT '第一次執(zhí)行時間',

`LAST_SEEN` timestamp NOT NULL DEFAULT '0000-00-00 00:00:00' COMMENT '最后一次執(zhí)行時間'

) ENGINE=PERFORMANCE_SCHEMA DEFAULT CHARSET=utf8

7，events_statements_summary_global_by_event_name：按照事件的語句進行聚合。表結構同上。

8，events_statements_summary_by_thread_by_event_name：按照線程和事件的語句進行聚合，表結構同上。

9，file_summary_by_instance：按事件類型統(tǒng)計（物理IO維度）

10，file_summary_by_event_name：具體文件統(tǒng)計（物理IO維度）

9和10一起說明：

統(tǒng)計IO操作：COUNT_STAR，SUM_TIMER_WAIT,MIN_TIMER_WAIT,AVG_TIMER_WAIT,MAX_TIMER_WAIT

統(tǒng)計讀：COUNT_READ,SUM_TIMER_READ,MIN_TIMER_READ,AVG_TIMER_READ,MAX_TIMER_READ, SUM_NUMBER_OF_BYTES_READ

統(tǒng)計寫：COUNT_WRITE,SUM_TIMER_WRITE,MIN_TIMER_WRITE,AVG_TIMER_WRITE,MAX_TIMER_WRITE, SUM_NUMBER_OF_BYTES_WRITE

統(tǒng)計其他IO事件，比如create，delete，open，close等：COUNT_MISC,SUM_TIMER_MISC,MIN_TIMER_MISC,AVG_TIMER_MISC,MAX_TIMER_MISC

11，table_io_waits_summary_by_table：根據(jù)wait/io/table/sql/handler，聚合每個表的I/O操作（邏輯IO緯度）

統(tǒng)計IO操作：COUNT_STAR,SUM_TIMER_WAIT,MIN_TIMER_WAIT,AVG_TIMER_WAIT,MAX_TIMER_WAIT

統(tǒng)計讀：COUNT_READ,SUM_TIMER_READ,MIN_TIMER_READ,AVG_TIMER_READ,MAX_TIMER_READ

：COUNT_FETCH,SUM_TIMER_FETCH,MIN_TIMER_FETCH,AVG_TIMER_FETCH, MAX_TIMER_FETCH

統(tǒng)計寫：COUNT_WRITE,SUM_TIMER_WRITE,MIN_TIMER_WRITE,AVG_TIMER_WRITE,MAX_TIMER_WRITE

INSERT統(tǒng)計，相應的還有DELETE和UPDATE統(tǒng)計：COUNT_INSERT,SUM_TIMER_INSERT,MIN_TIMER_INSERT,AVG_TIMER_INSERT,MAX_TIMER_INSERT

12，table_io_waits_summary_by_index_usage：與table_io_waits_summary_by_table類似，按索引維度統(tǒng)計

13，table_lock_waits_summary_by_table：聚合了表鎖等待事件，包括internal lock 和 external lock

internal lock通過SQL層函數(shù)thr_lock調用，OPERATION值為：
read normal、read with shared locks、read high priority、read no insert、write allow write、write concurrent insert、write delayed、write low priority、write normal
external lock則通過接口函數(shù)handler::external_lock調用存儲引擎層，OPERATION列的值為：read external、write external

14，Connection Summaries表：account、user、host

events_waits_summary_by_account_by_event_name
events_waits_summary_by_user_by_event_name
events_waits_summary_by_host_by_event_name
events_stages_summary_by_account_by_event_name
events_stages_summary_by_user_by_event_name
events_stages_summary_by_host_by_event_name
events_statements_summary_by_account_by_event_name
events_statements_summary_by_user_by_event_name
events_statements_summary_by_host_by_event_name

15，socket_summary_by_instance、socket_summary_by_event_name：socket聚合統(tǒng)計表。

八：其他相關表

1，performance_timers：系統(tǒng)支持的統(tǒng)計時間單位

2，threads：監(jiān)視服務端的當前運行的線程

統(tǒng)計應用：

關于SQL維度的統(tǒng)計信息主要集中在events_statements_summary_by_digest表中，通過將SQL語句抽象出digest，可以統(tǒng)計某類SQL語句在各個維度的統(tǒng)計信息

1，哪個SQL執(zhí)行最多：

zjy@performance_schema 11:36:22>SELECT SCHEMA_NAME,DIGEST_TEXT,COUNT_STAR,SUM_ROWS_SENT,SUM_ROWS_EXAMINED,FIRST_SEEN,LAST_SEEN FROM events_statements_summary_by_digest ORDER BY COUNT_STAR desc LIMIT 1\G

*************************** 1. row ***************************

SCHEMA_NAME: dchat

DIGEST_TEXT: SELECT ...

COUNT_STAR: 1161210102

SUM_ROWS_SENT: 1161207842

SUM_ROWS_EXAMINED:

FIRST_SEEN: 2016-02-17 00:36:46

LAST_SEEN: 2016-03-07 11:36:29

各個字段的注釋可以看上面的表結構說明：從2月17號到3月7號該SQL執(zhí)行了1161210102次。

2，哪個SQL平均響應時間最多：

zjy@performance_schema 11:36:28>SELECT SCHEMA_NAME,DIGEST_TEXT,COUNT_STAR,AVG_TIMER_WAIT,SUM_ROWS_SENT,SUM_ROWS_EXAMINED,FIRST_SEEN,LAST_SEEN FROM events_statements_summary_by_digest ORDER BY AVG_TIMER_WAIT desc LIMIT 1\G

*************************** 1. row ***************************

SCHEMA_NAME: dchat

DIGEST_TEXT: SELECT ...

COUNT_STAR: 1

AVG_TIMER_WAIT: 273238183964000

SUM_ROWS_SENT: 50208

SUM_ROWS_EXAMINED: 5565651

FIRST_SEEN: 2016-02-22 13:27:33

LAST_SEEN: 2016-02-22 13:27:33

各個字段的注釋可以看上面的表結構說明：從2月17號到3月7號該SQL平均響應時間273238183964000皮秒（1000000000000皮秒=1秒）

3，哪個SQL掃描的行數(shù)最多：

SUM_ROWS_EXAMINED

4，哪個SQL使用的臨時表最多：

SUM_CREATED_TMP_DISK_TABLES、SUM_CREATED_TMP_TABLES

5，哪個SQL返回的結果集最多：

SUM_ROWS_SENT

6，哪個SQL排序數(shù)最多：

SUM_SORT_ROWS

通過上述指標我們可以間接獲得某類SQL的邏輯IO(SUM_ROWS_EXAMINED)，CPU消耗(SUM_SORT_ROWS)，網(wǎng)絡帶寬(SUM_ROWS_SENT)的對比。

通過file_summary_by_instance表，可以獲得系統(tǒng)運行到現(xiàn)在，哪個文件(表)物理IO最多，這可能意味著這個表經(jīng)常需要訪問磁盤IO。

7，哪個表、文件邏輯IO最多（熱數(shù)據(jù)）：

zjy@performance_schema 12:16:18>SELECT FILE_NAME,EVENT_NAME,COUNT_READ,SUM_NUMBER_OF_BYTES_READ,COUNT_WRITE,SUM_NUMBER_OF_BYTES_WRITE FROM file_summary_by_instance ORDER BY SUM_NUMBER_OF_BYTES_READ+SUM_NUMBER_OF_BYTES_WRITE DESC LIMIT 2\G

*************************** 1. row ***************************

FILE_NAME: /var/lib/mysql/ibdata1 #文件

EVENT_NAME: wait/io/file/innodb/innodb_data_file

COUNT_READ: 544

SUM_NUMBER_OF_BYTES_READ: 10977280

COUNT_WRITE: 3700729

SUM_NUMBER_OF_BYTES_WRITE: 1433734217728

*************************** 2. row ***************************

FILE_NAME: /var/lib/mysql/dchat/fans.ibd #表

EVENT_NAME: wait/io/file/innodb/innodb_data_file

COUNT_READ: 9370680

SUM_NUMBER_OF_BYTES_READ: 153529188352

COUNT_WRITE: 67576376

SUM_NUMBER_OF_BYTES_WRITE: 1107815432192

8，哪個索引使用最多：

zjy@performance_schema 12:18:42>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 limit 1;

+-------------+------------+-------------+--------------+--------------+--------------+

+-------------+------------+-------------+--------------+--------------+--------------+

| fans | PRIMARY | 29002695158 | | 296373434 | |

+-------------+------------+-------------+--------------+--------------+--------------+

1 row in set (0.29 sec)

通過table_io_waits_summary_by_index_usage表，可以獲得系統(tǒng)運行到現(xiàn)在，哪個表的具體哪個索引(包括主鍵索引，二級索引)使用最多。

9，哪個索引沒有使用過：

zjy@performance_schema 12:23:22>SELECT OBJECT_SCHEMA, OBJECT_NAME, INDEX_NAME FROM table_io_waits_summary_by_index_usage WHERE INDEX_NAME IS NOT NULL AND COUNT_STAR = AND OBJECT_SCHEMA <> 'mysql' ORDER BY OBJECT_SCHEMA,OBJECT_NAME;

10，哪個等待事件消耗的時間最多：

zjy@performance_schema 12:25:22>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 LIMIT 1;

11，類似profiling功能：

分析具體某條SQL，該SQL在執(zhí)行各個階段的時間消耗，通過events_statements_xxx表和events_stages_xxx表，就可以達到目的。兩個表通過event_id與nesting_event_id關聯(lián)，stages表的nesting_event_id為對應statements表的event_id；針對每個stage可能出現(xiàn)的鎖等待，一個stage會對應一個或多個wait，通過stage_xxx表的event_id字段與waits_xxx表的nesting_event_id進行關聯(lián)。如：

比如分析包含count(*)的某條SQL語句，具體如下：

SELECT

EVENT_ID,

sql_text

FROM events_statements_history

WHERE sql_text LIKE '%count(*)%';

+----------+--------------------------------------+

| EVENT_ID | sql_text |

+----------+--------------------------------------+

| 1690 | select count(*) from chuck.test_slow |

+----------+--------------------------------------+

首先得到了語句的event_id為1690，通過查找events_stages_xxx中nesting_event_id為1690的記錄，可以達到目的。

a.查看每個階段的時間消耗：

SELECT

event_id,

EVENT_NAME,

SOURCE,

TIMER_END - TIMER_START

FROM events_stages_history_long

WHERE NESTING_EVENT_ID = 1690;

+----------+--------------------------------+----------------------+-----------------------+

+----------+--------------------------------+----------------------+-----------------------+

| 1691 | stage/sql/init | mysqld.cc:990 | 316945000 |

| 1693 | stage/sql/checking permissions | sql_parse.cc:5776 | 26774000 |

| 1695 | stage/sql/Opening tables | sql_base.cc:4970 | 41436934000 |

| 2638 | stage/sql/init | sql_select.cc:1050 | 85757000 |

| 2639 | stage/sql/System lock | lock.cc:303 | 40017000 |

| 2643 | stage/sql/optimizing | sql_optimizer.cc:138 | 38562000 |

| 2644 | stage/sql/statistics | sql_optimizer.cc:362 | 52845000 |

| 2645 | stage/sql/preparing | sql_optimizer.cc:485 | 53196000 |

| 2646 | stage/sql/executing | sql_executor.cc:112 | 3153000 |

| 2647 | stage/sql/Sending data | sql_executor.cc:192 | 7369072089000 |

| 4304138 | stage/sql/end | sql_select.cc:1105 | 19920000 |

| 4304139 | stage/sql/query end | sql_parse.cc:5463 | 44721000 |

| 4304145 | stage/sql/closing tables | sql_parse.cc:5524 | 61723000 |

| 4304152 | stage/sql/freeing items | sql_parse.cc:6838 | 455678000 |

| 4304155 | stage/sql/logging slow query | sql_parse.cc:2258 | 83348000 |

| 4304159 | stage/sql/cleaning up | sql_parse.cc:2163 | 4433000 |

+----------+--------------------------------+----------------------+-----------------------+

通過間接關聯(lián)，我們能分析得到SQL語句在每個階段的時間消耗，時間單位以皮秒表示。這里展示的結果很類似profiling功能，有了performance schema，就不再需要profiling這個功能了。另外需要注意的是，由于默認情況下events_stages_history表中只為每個連接記錄了最近10條記錄，為了確保獲取所有記錄，需要訪問events_stages_history_long表

b.查看某個階段的鎖等待情況

SELECT

event_id,

event_name,

source,

timer_wait,

object_name,

index_name,

operation,

nesting_event_id

FROM events_waits_history_long

WHERE nesting_event_id = 2647;

+----------+---------------------------+-----------------+------------+-------------+------------+-----------+------------------+

+----------+---------------------------+-----------------+------------+-------------+------------+-----------+------------------+

+----------+---------------------------+-----------------+------------+-------------+------------+-----------+------------------+

通過上面的實驗，我們知道了statement,stage,wait的三級結構，通過nesting_event_id進行關聯(lián)，它表示某個事件的父event_id。

(2).模擬innodb行鎖等待的例子

會話A執(zhí)行語句update test_icp set y=y+1 where x=1(x為primary key)，不commit；會話B執(zhí)行同樣的語句update test_icp set y=y+1 where x=1，會話B堵塞，并最終報錯。通過連接連接查詢events_statements_history_long和events_stages_history_long，可以看到在updating階段花了大約60s的時間。這主要因為實例上的innodb_lock_wait_timeout設置為60，等待60s后超時報錯了。

SELECT

statement.EVENT_ID,

stages.event_id,

statement.sql_text,

stages.event_name,

stages.timer_wait

FROM events_statements_history_long statement

join events_stages_history_long stages

on statement.event_id=stages.nesting_event_id

WHERE statement.sql_text = 'update test_icp set y=y+1 where x=1';

+----------+----------+-------------------------------------+--------------------------------+----------------+

+----------+----------+-------------------------------------+--------------------------------+----------------+

| 5816 | 5817 | update test_icp set y=y+1 where x=1 | stage/sql/init | 195543000 |

| 5816 | 5819 | update test_icp set y=y+1 where x=1 | stage/sql/checking permissions | 22730000 |

| 5816 | 5821 | update test_icp set y=y+1 where x=1 | stage/sql/Opening tables | 66079000 |

| 5816 | 5827 | update test_icp set y=y+1 where x=1 | stage/sql/init | 89116000 |

| 5816 | 5828 | update test_icp set y=y+1 where x=1 | stage/sql/System lock | 218744000 |

| 5816 | 5832 | update test_icp set y=y+1 where x=1 | stage/sql/updating | 6001362045000 |

| 5816 | 5968 | update test_icp set y=y+1 where x=1 | stage/sql/end | 10435000 |

| 5816 | 5969 | update test_icp set y=y+1 where x=1 | stage/sql/query end | 85979000 |

| 5816 | 5983 | update test_icp set y=y+1 where x=1 | stage/sql/closing tables | 56562000 |

| 5816 | 5990 | update test_icp set y=y+1 where x=1 | stage/sql/freeing items | 83563000 |

| 5816 | 5992 | update test_icp set y=y+1 where x=1 | stage/sql/cleaning up | 4589000 |

+----------+----------+-------------------------------------+--------------------------------+----------------+

查看wait事件：

SELECT

event_id,

event_name,

source,

timer_wait,

object_name,

index_name,

operation,

nesting_event_id

FROM events_waits_history_long

WHERE nesting_event_id = 5832;

*************************** 1. row ***************************

event_id: 5832

event_name: wait/io/table/sql/handler

source: handler.cc:2782

timer_wait: 6005946156624

object_name: test_icp

index_name: PRIMARY

operation: fetch

從結果來看，waits表中記錄了一個fetch等待事件，但并沒有更細的innodb行鎖等待事件統(tǒng)計。

(3).模擬MDL鎖等待的例子

會話A執(zhí)行一個大查詢select count(*) from test_slow，會話B執(zhí)行表結構變更alter table test_slow modify c2 varchar(152);通過如下語句可以得到alter語句的執(zhí)行過程，重點關注“stage/sql/Waiting for table metadata lock”階段。

SELECT

statement.EVENT_ID,

stages.event_id,

statement.sql_text,

stages.event_name as stage_name,

stages.timer_wait as stage_time

FROM events_statements_history_long statement

left join events_stages_history_long stages

on statement.event_id=stages.nesting_event_id

WHERE statement.sql_text = 'alter table test_slow modify c2 varchar(152)';

+-----------+-----------+----------------------------------------------+----------------------------------------------------+---------------+

+-----------+-----------+----------------------------------------------+----------------------------------------------------+---------------+

| 326526744 | 326526745 | alter table test_slow modify c2 varchar(152) | stage/sql/init | 216662000 |

| 326526744 | 326526747 | alter table test_slow modify c2 varchar(152) | stage/sql/checking permissions | 18183000 |

| 326526744 | 326526748 | alter table test_slow modify c2 varchar(152) | stage/sql/checking permissions | 10294000 |

| 326526744 | 326526750 | alter table test_slow modify c2 varchar(152) | stage/sql/init | 4783000 |

| 326526744 | 326526751 | alter table test_slow modify c2 varchar(152) | stage/sql/Opening tables | 140172000 |

| 326526744 | 326526760 | alter table test_slow modify c2 varchar(152) | stage/sql/setup | 157643000 |

| 326526744 | 326526769 | alter table test_slow modify c2 varchar(152) | stage/sql/creating table | 8723217000 |

| 326526744 | 326526803 | alter table test_slow modify c2 varchar(152) | stage/sql/After create | 257332000 |

| 326526744 | 326526832 | alter table test_slow modify c2 varchar(152) | stage/sql/Waiting for table metadata lock | 1000181831000 |

| 326526744 | 326526835 | alter table test_slow modify c2 varchar(152) | stage/sql/After create | 33483000 |

| 326526744 | 326526838 | alter table test_slow modify c2 varchar(152) | stage/sql/Waiting for table metadata lock | 1000091810000 |

| 326526744 | 326526841 | alter table test_slow modify c2 varchar(152) | stage/sql/After create | 17187000 |

| 326526744 | 326526844 | alter table test_slow modify c2 varchar(152) | stage/sql/Waiting for table metadata lock | 1000126464000 |

| 326526744 | 326526847 | alter table test_slow modify c2 varchar(152) | stage/sql/After create | 27472000 |

| 326526744 | 326526850 | alter table test_slow modify c2 varchar(152) | stage/sql/Waiting for table metadata lock | 561996133000 |

| 326526744 | 326526853 | alter table test_slow modify c2 varchar(152) | stage/sql/After create | 124876000 |

| 326526744 | 326526877 | alter table test_slow modify c2 varchar(152) | stage/sql/System lock | 30659000 |

| 326526744 | 326526881 | alter table test_slow modify c2 varchar(152) | stage/sql/preparing for alter table | 40246000 |

| 326526744 | 326526889 | alter table test_slow modify c2 varchar(152) | stage/sql/altering table | 36628000 |

| 326526744 | 326528280 | alter table test_slow modify c2 varchar(152) | stage/sql/end | 43824000 |

| 326526744 | 326528281 | alter table test_slow modify c2 varchar(152) | stage/sql/query end | 112557000 |

| 326526744 | 326528299 | alter table test_slow modify c2 varchar(152) | stage/sql/closing tables | 27707000 |

| 326526744 | 326528305 | alter table test_slow modify c2 varchar(152) | stage/sql/freeing items | 201614000 |

| 326526744 | 326528308 | alter table test_slow modify c2 varchar(152) | stage/sql/cleaning up | 3584000 |

+-----------+-----------+----------------------------------------------+----------------------------------------------------+---------------+

從結果可以看到，出現(xiàn)了多次stage/sql/Waiting for table metadata lock階段，并且間隔1s，說明每隔1s鐘會重試判斷。找一個該階段的event_id,通過nesting_event_id關聯(lián)，確定到底在等待哪個wait事件。

SELECT

event_id,

event_name,

source,

timer_wait,

object_name,

index_name,

operation,

nesting_event_id

FROM events_waits_history_long

WHERE nesting_event_id = 326526850;

+-----------+---------------------------------------------------+------------------+--------------+-------------+------------+------------+------------------+

+-----------+---------------------------------------------------+------------------+--------------+-------------+------------+------------+------------------+

+-----------+---------------------------------------------------+------------------+--------------+-------------+------------+------------+------------------+

通過結果可以知道，產(chǎn)生阻塞的是條件變量MDL_context::COND_wait_status，并且顯示了代碼的位置。

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