21.1. Performance Schema Quick Start

This section briefly introduces the Performance Schema with examples that show how to use it. For additional examples, see Section 21.15, "Using the Performance Schema to Diagnose Problems".

For the Performance Schema to be available, support for it must have been configured when MySQL was built. You can verify whether this is the case by checking the server's help output. If the Performance Schema is available, the output will mention several variables with names that begin with performance_schema:

shell> mysqld --verbose --help...  --performance_schema                      Enable the performance schema.  --performance_schema_events_waits_history_long_size=#                      Number of rows in events_waits_history_long....

If such variables do not appear in the output, your server has not been built to support the Performance Schema. In this case, see Section 21.2, "Performance Schema Configuration".

Assuming that the Performance Schema is available, it is enabled by default as of MySQL 5.6.6. Before 5.6.6, it is disabled by default. To enable or disable it explicitly, start the server with the performance_schema variable set to an appropriate value. For example, use these lines in your my.cnf file:

[mysqld]performance_schema=on

When the server starts, it sees performance_schema and attempts to initialize the Performance Schema. To verify successful initialization, use this statement:

mysql> SHOW VARIABLES LIKE
        'performance_schema';+--------------------+-------+| Variable_name      | Value |+--------------------+-------+| performance_schema | ON    |+--------------------+-------+

A value of ON means that the Performance Schema initialized successfully and is ready for use. A value of OFF means that some error occurred. Check the server error log for information about what went wrong.

The Performance Schema is implemented as a storage engine. If this engine is available (which you should already have checked earlier), you should see it listed with a SUPPORT value of YES in the output from the INFORMATION_SCHEMA.ENGINES table or the SHOW ENGINES statement:

mysql> SELECT * FROM
        INFORMATION_SCHEMA.ENGINES    -> WHERE
        ENGINE='PERFORMANCE_SCHEMA'\G*************************** 1. row ***************************      ENGINE: PERFORMANCE_SCHEMA     SUPPORT: YES     COMMENT: Performance SchemaTRANSACTIONS: NO          XA: NO  SAVEPOINTS: NOmysql> SHOW ENGINES\G...      Engine: PERFORMANCE_SCHEMA     Support: YES     Comment: Performance SchemaTransactions: NO          XA: NO  Savepoints: NO...

The PERFORMANCE_SCHEMA storage engine operates on tables in the performance_schema database. You can make performance_schema the default database so that references to its tables need not be qualified with the database name:

mysql> USE performance_schema;

Many examples in this chapter assume that performance_schema is the default database.

Performance Schema tables are stored in the performance_schema database. Information about the structure of this database and its tables can be obtained, as for any other database, by selecting from the INFORMATION_SCHEMA database or by using SHOW statements. For example, use either of these statements to see what Performance Schema tables exist:

mysql> SELECT TABLE_NAME FROM
        INFORMATION_SCHEMA.TABLES    -> WHERE TABLE_SCHEMA =
        'performance_schema';+----------------------------------------------------+| TABLE_NAME                                         |+----------------------------------------------------+| accounts                                           || cond_instances                                     || 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         || events_statements_current                          || events_statements_history                          || events_statements_history_long                     |...| file_instances                                     || file_summary_by_event_name                         || file_summary_by_instance                           || host_cache                                         || hosts                                              || mutex_instances                                    || objects_summary_global_by_type                     || performance_timers                                 || rwlock_instances                                   || session_account_connect_attrs                      || session_connect_attrs                              || setup_actors                                       || setup_consumers                                    || setup_instruments                                  || setup_objects                                      || setup_timers                                       || socket_instances                                   || socket_summary_by_event_name                       || socket_summary_by_instance                         || table_io_waits_summary_by_index_usage              || table_io_waits_summary_by_table                    || table_lock_waits_summary_by_table                  || threads                                            || users                                              |+----------------------------------------------------+mysql> SHOW TABLES FROM performance_schema;+----------------------------------------------------+| Tables_in_performance_schema                       |+----------------------------------------------------+| accounts                                           || cond_instances                                     || events_stages_current                              || events_stages_history                              || events_stages_history_long                         |...

The number of Performance Schema tables is expected to increase over time as implementation of additional instrumentation proceeds.

The name of the performance_schema database is lowercase, as are the names of tables within it. Queries should specify the names in lowercase.

To see the structure of individual tables, use SHOW CREATE TABLE:

mysql> SHOW CREATE TABLE
        setup_timers\G*************************** 1. row ***************************       Table: setup_timersCreate Table: CREATE TABLE `setup_timers` (  `NAME` varchar(64) NOT NULL,  `TIMER_NAME` enum('CYCLE','NANOSECOND','MICROSECOND','MILLISECOND','TICK')   NOT NULL) ENGINE=PERFORMANCE_SCHEMA DEFAULT CHARSET=utf8

Table structure is also available by selecting from tables such as INFORMATION_SCHEMA.COLUMNS or by using statements such as SHOW COLUMNS.

Tables in the performance_schema database can be grouped according to the type of information in them: Current events, event histories and summaries, object instances, and setup (configuration) information. The following examples illustrate a few uses for these tables. For detailed information about the tables in each group, see Section 21.9, "Performance Schema Table Descriptions".

To see what the server is doing at the moment, examine the events_waits_current table. It contains one row per thread showing each thread's most recent monitored event:

mysql> SELECT * FROM
        events_waits_current\G*************************** 1. row ***************************            THREAD_ID: 0             EVENT_ID: 5523           EVENT_NAME: wait/synch/mutex/mysys/THR_LOCK::mutex               SOURCE: thr_lock.c:525          TIMER_START: 201660494489586            TIMER_END: 201660494576112           TIMER_WAIT: 86526                SPINS: NULL        OBJECT_SCHEMA: NULL          OBJECT_NAME: NULL          OBJECT_TYPE: NULLOBJECT_INSTANCE_BEGIN: 142270668     NESTING_EVENT_ID: NULL            OPERATION: lock      NUMBER_OF_BYTES: NULL                FLAGS: 0...

This event indicates that thread 0 was waiting for 86,526 picoseconds to acquire a lock on THR_LOCK::mutex, a mutex in the mysys subsystem. The first few columns provide the following information:

The ID columns indicate which thread the event comes from and the event number.
EVENT_NAME indicates what was instrumented and SOURCE indicates which source file contains the instrumented code.
The timer columns show when the event started and stopped and how long it took. If an event is still in progress, the TIMER_END and TIMER_WAIT values are NULL. Timer values are approximate and expressed in picoseconds. For information about timers and event time collection, see Section 21.2.3.1, "Performance Schema Event Timing".

The history tables contain the same kind of rows as the current-events table but have more rows and show what the server has been doing "recently" rather than "currently." The events_waits_history and events_waits_history_long tables contain the most recent 10 events per thread and most recent 10,000 events, respectively. For example, to see information for recent events produced by thread 13, do this:

mysql> SELECT EVENT_ID, EVENT_NAME, TIMER_WAIT    -> FROM events_waits_history WHERE THREAD_ID = 13    -> ORDER BY EVENT_ID;+----------+-----------------------------------------+------------+| EVENT_ID | EVENT_NAME                              | TIMER_WAIT |+----------+-----------------------------------------+------------+|       86 | wait/synch/mutex/mysys/THR_LOCK::mutex  |     686322 ||       87 | wait/synch/mutex/mysys/THR_LOCK_malloc  |     320535 ||       88 | wait/synch/mutex/mysys/THR_LOCK_malloc  |     339390 ||       89 | wait/synch/mutex/mysys/THR_LOCK_malloc  |     377100 ||       90 | wait/synch/mutex/sql/LOCK_plugin        |     614673 ||       91 | wait/synch/mutex/sql/LOCK_open          |     659925 ||       92 | wait/synch/mutex/sql/THD::LOCK_thd_data |     494001 ||       93 | wait/synch/mutex/mysys/THR_LOCK_malloc  |     222489 ||       94 | wait/synch/mutex/mysys/THR_LOCK_malloc  |     214947 ||       95 | wait/synch/mutex/mysys/LOCK_alarm       |     312993 |+----------+-----------------------------------------+------------+

As new events are added to a history table, older events are discarded if the table is full.

Summary tables provide aggregated information for all events over time. The tables in this group summarize event data in different ways. To see which instruments have been executed the most times or have taken the most wait time, sort the events_waits_summary_global_by_event_name table on the COUNT_STAR or SUM_TIMER_WAIT column, which correspond to a COUNT(*) or SUM(TIMER_WAIT) value, respectively, calculated over all events:

mysql> SELECT EVENT_NAME, COUNT_STAR    -> FROM events_waits_summary_global_by_event_name    -> ORDER BY COUNT_STAR DESC LIMIT 10;+---------------------------------------------------+------------+| EVENT_NAME                                        | COUNT_STAR |+---------------------------------------------------+------------+| wait/synch/mutex/mysys/THR_LOCK_malloc            |       6419 || wait/io/file/sql/FRM                              |        452 || wait/synch/mutex/sql/LOCK_plugin                  |        337 || wait/synch/mutex/mysys/THR_LOCK_open              |        187 || wait/synch/mutex/mysys/LOCK_alarm                 |        147 || wait/synch/mutex/sql/THD::LOCK_thd_data           |        115 || wait/io/file/myisam/kfile                         |        102 || wait/synch/mutex/sql/LOCK_global_system_variables |         89 || wait/synch/mutex/mysys/THR_LOCK::mutex            |         89 || wait/synch/mutex/sql/LOCK_open                    |         88 |+---------------------------------------------------+------------+mysql> SELECT EVENT_NAME, SUM_TIMER_WAIT    -> FROM events_waits_summary_global_by_event_name    -> ORDER BY SUM_TIMER_WAIT DESC LIMIT 10;+----------------------------------------+----------------+| EVENT_NAME                             | SUM_TIMER_WAIT |+----------------------------------------+----------------+| wait/io/file/sql/MYSQL_LOG             |     1599816582 || wait/synch/mutex/mysys/THR_LOCK_malloc |     1530083250 || wait/io/file/sql/binlog_index          |     1385291934 || wait/io/file/sql/FRM                   |     1292823243 || wait/io/file/myisam/kfile              |      411193611 || wait/io/file/myisam/dfile              |      322401645 || wait/synch/mutex/mysys/LOCK_alarm      |      145126935 || wait/io/file/sql/casetest              |      104324715 || wait/synch/mutex/sql/LOCK_plugin       |       86027823 || wait/io/file/sql/pid                   |       72591750 |+----------------------------------------+----------------+

These results show that the THR_LOCK_malloc mutex is "hot," both in terms of how often it is used and amount of time that threads wait attempting to acquire it.

Note

The THR_LOCK_malloc mutex is used only in debug builds. In production builds it is not hot because it is nonexistent.

Instance tables document what types of objects are instrumented. An instrumented object, when used by the server, produces an event. These tables provide event names and explanatory notes or status information. For example, the file_instances table lists instances of instruments for file I/O operations and their associated files:

mysql> SELECT * FROM file_instances\G*************************** 1. row *************************** FILE_NAME: /opt/mysql-log/60500/binlog.000007EVENT_NAME: wait/io/file/sql/binlogOPEN_COUNT: 0*************************** 2. row *************************** FILE_NAME: /opt/mysql/60500/data/mysql/tables_priv.MYIEVENT_NAME: wait/io/file/myisam/kfileOPEN_COUNT: 1*************************** 3. row *************************** FILE_NAME: /opt/mysql/60500/data/mysql/columns_priv.MYIEVENT_NAME: wait/io/file/myisam/kfileOPEN_COUNT: 1...

Setup tables are used to configure and display monitoring characteristics. For example, to see which event timers are selected, query the setup_timers tables:

mysql> SELECT * FROM setup_timers;+-----------+-------------+| NAME      | TIMER_NAME  |+-----------+-------------+| idle      | MICROSECOND || wait      | CYCLE       || stage     | NANOSECOND  || statement | NANOSECOND  |+-----------+-------------+

setup_instruments lists the set of instruments for which events can be collected and shows which of them are enabled:

mysql> SELECT * FROM
        setup_instruments;+------------------------------------------------------------+---------+-------+| NAME                                                       | ENABLED | TIMED |+------------------------------------------------------------+---------+-------+...| wait/synch/mutex/sql/LOCK_global_read_lock                 | YES     | YES   || wait/synch/mutex/sql/LOCK_global_system_variables          | YES     | YES   || wait/synch/mutex/sql/LOCK_lock_db                          | YES     | YES   || wait/synch/mutex/sql/LOCK_manager                          | YES     | YES   |...| wait/synch/rwlock/sql/LOCK_grant                           | YES     | YES   || wait/synch/rwlock/sql/LOGGER::LOCK_logger                  | YES     | YES   || wait/synch/rwlock/sql/LOCK_sys_init_connect                | YES     | YES   || wait/synch/rwlock/sql/LOCK_sys_init_slave                  | YES     | YES   |...| wait/io/file/sql/binlog                                    | YES     | YES   || wait/io/file/sql/binlog_index                              | YES     | YES   || wait/io/file/sql/casetest                                  | YES     | YES   || wait/io/file/sql/dbopt                                     | YES     | YES   |...

To understand how to interpret instrument names, see Section 21.4, "Performance Schema Instrument Naming Conventions".

To control whether events are collected for an instrument, set its ENABLED value to YES or NO. For example:

mysql> UPDATE setup_instruments SET ENABLED =
        'NO'    -> WHERE NAME =
        'wait/synch/mutex/sql/LOCK_mysql_create_db';

The Performance Schema uses collected events to update tables in the performance_schema database, which act as "consumers" of event information. The setup_consumers table lists the available consumers and which are enabled:

mysql> 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     |+--------------------------------+---------+

To control whether the Performance Schema maintains a consumer as a destination for event information, set its ENABLED value.

For more information about the setup tables and how to use them to control event collection, see Section 21.2.3.2, "Performance Schema Event Filtering".

There are some miscellaneous tables that do not fall into any of the previous groups. For example, performance_timers lists the available event timers and their characteristics. For information about timers, see Section 21.2.3.1, "Performance Schema Event Timing".