22.17.1 Query Profiling Using Performance Schema

The following example demonstrates how to use Performance Schema statement events and stage events to retrieve data comparable to profiling information provided by SHOW PROFILES and SHOW PROFILE statements.

In this example, statement and stage event data is collected in the events_statements_history_long and events_stages_history_long tables. On a busy server with many active foreground threads, data could age out of the history tables before you are able to retrieve the information you want to analyze. If you encounter this problem, options include:

• Running the query on a test instance where there is less foreground thread activity.

• Disabling instrumentation for other existing foreground threads by setting the INSTRUMENTED field of the threads table to NO for other thread records. For example, the following statement disables instrumentation for all foreground threads except the test_user thread:

  mysql> UPDATE performance_schema.threads
         SET INSTRUMENTED = 'NO'
         WHERE TYPE='FOREGROUND' AND PROCESSLIST_USER NOT LIKE 'test_user';

  However, be aware that new threads are always instrumented by default.

• Increasing the number of rows in the events_statements_history_long and events_stages_history_long tables. The performance_schema_events_statements_history_size and performance_schema_events_stages_history_size configuration options are autosized by default but can also be set explicitly at startup. You can view current settings by running SHOW VARIABLES. For information about autosized Performance Schema parameters, see Section 22.3, “Performance Schema Startup Configuration”.

Performance Schema displays event timer information in picoseconds (trillionths of a second) to normalize timing data to a standard unit. In the following example, TIMER_WAIT values are divided by 1000000000000 to show data in units of seconds. Values are also truncated to 6 decimal places to display data in the same format as SHOW PROFILES and SHOW PROFILE statements.

1. Ensure that statement and stage instrumentation is enabled by updating the setup_instruments table. Some instruments may already be enabled by default.

   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/%';

2. Ensure that events_statements_* and events_stages_* consumers are enabled. Some consumers may already be enabled by default.

   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_%';

3. Run the statement that you want to profile. For example:

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

4. Identify the EVENT_ID of the statement by querying the events_statements_history_long table. This step is similar to running SHOW PROFILES to identify the Query_ID. The following query produces output similar to 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 |
   +----------+----------+--------------------------------------------------------+

5. Query the events_stages_history_long table to retrieve the statement's stage events. Stages are linked to statements using event nesting. Each stage event record has a NESTING_EVENT_ID column that contains the EVENT_ID of the parent statement.

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