Performance Schema 实现了一些系统变量，这些变量提供配置信息。

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 系统变量可以在服务器启动时通过命令行或选项文件设置，并且许多变量可以在运行时设置。请参见第 29.13 节，“Performance Schema 选项和变量参考”。

如果 Performance Schema 的几个参数没有明确设置，那么 Performance Schema 会在服务器启动时自动确定这些参数的值。有关更多信息，请参见第 29.3 节，“Performance Schema 启动配置”。

Performance Schema 系统变量具有以下含义。