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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  /  25.19.1 使用性能模式进行查询分析

25.19.1 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 PROFILESSHOW PROFILE语句提供的分析信息相当的数据。

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 PROFILESSHOW PROFILE语句相同的格式显示数据。

  1. 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:

    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:

    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:

    mysql> SELECT * FROM performance_schema.setup_actors;
    +-----------+-----------+------+---------+---------+
    | HOST      | USER      | ROLE | ENABLED | HISTORY |
    +-----------+-----------+------+---------+---------+
    | %         | %         | %    | NO      | NO      |
    | localhost | test_user | %    | YES     | YES     |
    +-----------+-----------+------+---------+---------+
  2. 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。

    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/%';
  3. 确保events_statements_*启用 events_stages_*消费者。一些消费者可能已经默认启用。

    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_%';
  4. 在您正在监视的用户帐户下,运行您要分析的语句。例如:

    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 |
    +--------+------------+------------+-----------+--------+------------+
  5. 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

    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 |
    +----------+----------+--------------------------------------------------------+
  6. 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。

    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 |
    +--------------------------------+----------+