Performance Schema 實作多個系統變數，以提供組態資訊

mysql> SHOW VARIABLES LIKE 'perf%';
+----------------------------------------------------------+-------+
| Variable_name                                            | Value |
+----------------------------------------------------------+-------+
| performance_schema                                       | ON    |
| performance_schema_accounts_size                         | -1    |
| performance_schema_digests_size                          | 10000 |
| performance_schema_error_size                            | 5377  |
| performance_schema_events_stages_history_long_size       | 10000 |
| performance_schema_events_stages_history_size            | 10    |
| performance_schema_events_statements_history_long_size   | 10000 |
| performance_schema_events_statements_history_size        | 10    |
| performance_schema_events_transactions_history_long_size | 10000 |
| performance_schema_events_transactions_history_size      | 10    |
| performance_schema_events_waits_history_long_size        | 10000 |
| performance_schema_events_waits_history_size             | 10    |
| performance_schema_hosts_size                            | -1    |
| performance_schema_max_cond_classes                      | 150   |
| performance_schema_max_cond_instances                    | -1    |
| performance_schema_max_digest_length                     | 1024  |
| performance_schema_max_digest_sample_age                 | 60    |
| performance_schema_max_file_classes                      | 80    |
| performance_schema_max_file_handles                      | 32768 |
| performance_schema_max_file_instances                    | -1    |
| performance_schema_max_index_stat                        | -1    |
| performance_schema_max_memory_classes                    | 470   |
| performance_schema_max_metadata_locks                    | -1    |
| performance_schema_max_meter_classes                     | 30    |
| performance_schema_max_metric_classes                    | 600   |
| performance_schema_max_mutex_classes                     | 350   |
| performance_schema_max_mutex_instances                   | -1    |
| performance_schema_max_prepared_statements_instances     | -1    |
| performance_schema_max_program_instances                 | -1    |
| performance_schema_max_rwlock_classes                    | 100   |
| performance_schema_max_rwlock_instances                  | -1    |
| performance_schema_max_socket_classes                    | 10    |
| performance_schema_max_socket_instances                  | -1    |
| performance_schema_max_sql_text_length                   | 1024  |
| performance_schema_max_stage_classes                     | 175   |
| performance_schema_max_statement_classes                 | 220   |
| performance_schema_max_statement_stack                   | 10    |
| performance_schema_max_table_handles                     | -1    |
| performance_schema_max_table_instances                   | -1    |
| performance_schema_max_table_lock_stat                   | -1    |
| performance_schema_max_thread_classes                    | 100   |
| performance_schema_max_thread_instances                  | -1    |
| performance_schema_session_connect_attrs_size            | 512   |
| performance_schema_setup_actors_size                     | -1    |
| performance_schema_setup_objects_size                    | -1    |
| performance_schema_show_processlist                      | OFF   |
| performance_schema_users_size                            | -1    |
+----------------------------------------------------------+-------+

Performance Schema 系統變數可在伺服器啟動時，於命令列或選項檔案中設定，而且許多變數可在執行階段設定。請參閱第 29.13 節，「Performance Schema 選項與變數參考」。

如果未明確設定，Performance Schema 會在伺服器啟動時，自動調整其多個參數的值。如需更多資訊，請參閱第 29.3 節，「Performance Schema 啟動設定」。

Performance Schema 系統變數具有下列含義