Performance Schema Overview

The Performance Schema is a feature for monitoring server performance.

Introduction

It is implemented as a storage engine, and so will appear in the list of storage engines available.

SHOW ENGINES;
+--------------------+---------+----------------------------------+--------------+------+------------+
| Engine             | Support | Comment                          | Transactions | XA   | Savepoints |
+--------------------+---------+----------------------------------+--------------+------+------------+
| ...                |         |                                  |              |      |            |
| PERFORMANCE_SCHEMA | YES     | Performance Schema               | NO           | NO   | NO         |
| ...                |         |                                  |              |      |            |
+--------------------+---------+----------------------------------+--------------+------+------------+

However, performance_schema is not a regular storage engine for storing data, it's a mechanism for implementing the Performance Schema feature.

The storage engine contains a database called performance_schema, which in turn consists of a number of tables that can be queried with regular SQL statements, returning specific performance information.

USE performance_schema

SHOW TABLES;
+----------------------------------------------------+
| Tables_in_performance_schema                       |
+----------------------------------------------------+
| accounts                                           |
...
| users                                              |
+----------------------------------------------------+
80 rows in set (0.00 sec)

See List of Performance Schema Tables for a full list and links to detailed descriptions of each table. From MariaDB 10.5, there are 80 Performance Schema tables, while until MariaDB 10.4, there are 52.

Activating the Performance Schema

The performance schema is disabled by default for performance reasons. You can check its current status by looking at the value of the performance_schema system variable.

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

The performance schema cannot be activated at runtime - it must be set when the server starts by adding the following line in your my.cnf configuration file.

performance_schema=ON

Until MariaDB 10.4, all memory used by the Performance Schema is allocated at startup. From MariaDB 10.5, some memory is allocated dynamically, depending on load, number of connections, number of tables open etc.

Enabling the Performance Schema

You need to set up all consumers (starting collection of data) and instrumentations (what to collect):

UPDATE performance_schema.setup_consumers SET ENABLED = 'YES';
UPDATE performance_schema.setup_instruments SET ENABLED = 'YES', TIMED = 'YES';

You can decide what to enable/disable with WHERE NAME like "%what_to_enable"; You can disable instrumentations by setting ENABLED to "NO".

You can also do this in your my.cnf file. The following enables all instrumentation of all stages (computation units) in MariaDB:

[mysqld]
performance_schema=ON
performance-schema-instrument='stage/%=ON'
performance-schema-consumer-events-stages-current=ON
performance-schema-consumer-events-stages-history=ON
performance-schema-consumer-events-stages-history-long=ON

Listing Performance Schema Variables

SHOW VARIABLES LIKE "perf%";
+--------------------------------------------------------+-------+
| Variable_name                                          | Value |
+--------------------------------------------------------+-------+
| performance_schema                                     | ON    |
...
| performance_schema_users_size                          | 100   |
+--------------------------------------------------------+-------+

See Performance Schema System Variables for a full list of available system variables.

Note that the "consumer" events are not shown on this list, as they are only available as options, not as system variables, and they can only be enabled at startup.

Column Comments

SELECT column_name, column_comment FROM information_schema.columns 
  WHERE table_schema='performance_schema' AND table_name='file_instances';
...
*************************** 2. row ***************************
   column_name: EVENT_NAME
column_comment: Instrument name associated with the file.
*************************** 3. row ***************************
   column_name: OPEN_COUNT
column_comment: Open handles on the file. A value of greater than zero means 
                that the file is currently open.
...

See Also

• Performance schema options
• SHOW ENGINE STATUS
• SHOW PROFILE
• ANALYZE STATEMENT
• Performance schema in MySQL 5.6. All things here should also work for MariaDB.