Panoramica sul Performance Schema

Instroduzione

Il Performance Schema è una funzionalità che serve a monitorare le performance del server, introdotta in MariaDB 5.5.3.

E' implementato come Storage Engine, pertanto compare nella lista degli Storage Engine disponibili.

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

Tuttavia PERFORMANCE_SCHEMA non è un normale Storage Engine per registrare i dati, ma è un meccanismo per implementare la funzionalità Performance Schema.

Lo Storage Engine contiene un database chiamato performance_schema, che a sua volta contiene un certo numero di tabelle che possono essere interrogate con normali istruzioni SQL, che restituiscono informazioni specifiche riguardanti le performance.

USE performance_schema;

SHOW TABLES;
+----------------------------------------------------+
| Tables_in_performance_schema                       |
+----------------------------------------------------+
| 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                     |
| events_statements_summary_by_account_by_event_name |
| events_statements_summary_by_digest                |
| events_statements_summary_by_host_by_event_name    |
| events_statements_summary_by_thread_by_event_name  |
| events_statements_summary_by_user_by_event_name    |
| events_statements_summary_global_by_event_name     |
| events_waits_current                               |
| events_waits_history                               |
| events_waits_history_long                          |
| events_waits_summary_by_account_by_event_name      |
| events_waits_summary_by_host_by_event_name         |
| events_waits_summary_by_instance                   |
| events_waits_summary_by_thread_by_event_name       |
| events_waits_summary_by_user_by_event_name         |
| events_waits_summary_global_by_event_name          |
| 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                                              |
+----------------------------------------------------+

Attivare il Performance Schema

Per default, il performance schema è disabilitato. Per conoscerne lo stato si può controllare la variabile di sistema performance_schema.

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

Il performance schema non può essere attivato a runtime - deve essere attivato all'avvio del server impostando la riga seguente nel file di configurazione my.cnf.

performance_schema=on