27.19.1 使用性能模式进行查询分析

MySQL 8.0 参考手册 / 第 27 章 MySQL 性能模式 / 27.19 使用性能模式诊断问题 / 27.19.1 使用性能模式进行查询分析

27.19.1 使用性能模式进行查询分析

以下示例演示如何使用 Performance Schema 语句事件和阶段事件来检索SHOW PROFILES与SHOW PROFILE语句提供的分析信息相当的数据。

该setup_actors表可用于按主机、用户或帐户限制历史事件的收集，以减少运行时开销和历史表中收集的数据量。该示例的第一步显示了如何将历史事件的收集限制为特定用户。

Performance Schema 以皮秒（万亿分之一秒）为单位显示事件计时器信息，以将计时数据规范化为标准单位。在以下示例中， TIMER_WAIT值除以 1000000000000 以秒为单位显示数据。值也被截断为小数点后 6 位，以便以SHOW PROFILES与 SHOW PROFILE语句相同的格式显示数据。

将历史事件的收集限制为运行查询的用户。默认情况下， setup_actors配置为允许对所有前台线程进行监控和历史事件收集：

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mysql> SELECT * FROM performance_schema.setup_actors;
+------+------+------+---------+---------+
| HOST | USER | ROLE | ENABLED | HISTORY |
+------+------+------+---------+---------+
| %    | %    | %    | YES     | YES     |
+------+------+------+---------+---------+

更新表中的默认行 setup_actors以禁用所有前台线程的历史事件收集和监视，并插入一个新行以启用对运行查询的用户的监视和历史事件收集：

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mysql> UPDATE performance_schema.setup_actors
       SET ENABLED = 'NO', HISTORY = 'NO'
       WHERE HOST = '%' AND USER = '%';

mysql> INSERT INTO performance_schema.setup_actors
       (HOST,USER,ROLE,ENABLED,HISTORY)
       VALUES('localhost','test_user','%','YES','YES');

表中的数据setup_actors现在应类似于以下内容：

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mysql> SELECT * FROM performance_schema.setup_actors;
+-----------+-----------+------+---------+---------+
| HOST      | USER      | ROLE | ENABLED | HISTORY |
+-----------+-----------+------+---------+---------+
| %         | %         | %    | NO      | NO      |
| localhost | test_user | %    | YES     | YES     |
+-----------+-----------+------+---------+---------+

确保通过更新 setup_instruments表启用语句和阶段检测。某些仪器可能已经默认启用。

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mysql> UPDATE performance_schema.setup_instruments
       SET ENABLED = 'YES', TIMED = 'YES'
       WHERE NAME LIKE '%statement/%';

mysql> UPDATE performance_schema.setup_instruments
       SET ENABLED = 'YES', TIMED = 'YES'
       WHERE NAME LIKE '%stage/%';

确保events_statements_*启用 events_stages_*消费者。一些消费者可能已经默认启用。

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mysql> UPDATE performance_schema.setup_consumers
       SET ENABLED = 'YES'
       WHERE NAME LIKE '%events_statements_%';

mysql> UPDATE performance_schema.setup_consumers
       SET ENABLED = 'YES'
       WHERE NAME LIKE '%events_stages_%';

在您正在监视的用户帐户下，运行您要分析的语句。例如：

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mysql> SELECT * FROM employees.employees WHERE emp_no = 10001;
+--------+------------+------------+-----------+--------+------------+
| emp_no | birth_date | first_name | last_name | gender | hire_date |
+--------+------------+------------+-----------+--------+------------+
|  10001 | 1953-09-02 | Georgi     | Facello   | M      | 1986-06-26 |
+--------+------------+------------+-----------+--------+------------+

EVENT_ID通过查询表来识别语句的所在events_statements_history_long 。这一步类似于运行 SHOW PROFILES识别 Query_ID。以下查询产生类似于的输出SHOW PROFILES：

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mysql> SELECT EVENT_ID, TRUNCATE(TIMER_WAIT/1000000000000,6) as Duration, SQL_TEXT
       FROM performance_schema.events_statements_history_long WHERE SQL_TEXT like '%10001%';
+----------+----------+--------------------------------------------------------+
| event_id | duration | sql_text                                               |
+----------+----------+--------------------------------------------------------+
|       31 | 0.028310 | SELECT * FROM employees.employees WHERE emp_no = 10001 |
+----------+----------+--------------------------------------------------------+

查询 events_stages_history_long 表以检索语句的阶段事件。阶段使用事件嵌套链接到语句。每个阶段事件记录都有一个NESTING_EVENT_ID包含EVENT_ID父语句的列。

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mysql> SELECT event_name AS Stage, TRUNCATE(TIMER_WAIT/1000000000000,6) AS Duration
       FROM performance_schema.events_stages_history_long WHERE NESTING_EVENT_ID=31;
+--------------------------------+----------+
| Stage                          | Duration |
+--------------------------------+----------+
| stage/sql/starting             | 0.000080 |
| stage/sql/checking permissions | 0.000005 |
| stage/sql/Opening tables       | 0.027759 |
| stage/sql/init                 | 0.000052 |
| stage/sql/System lock          | 0.000009 |
| stage/sql/optimizing           | 0.000006 |
| stage/sql/statistics           | 0.000082 |
| stage/sql/preparing            | 0.000008 |
| stage/sql/executing            | 0.000000 |
| stage/sql/Sending data         | 0.000017 |
| stage/sql/end                  | 0.000001 |
| stage/sql/query end            | 0.000004 |
| stage/sql/closing tables       | 0.000006 |
| stage/sql/freeing items        | 0.000272 |
| stage/sql/cleaning up          | 0.000001 |
+--------------------------------+----------+