Performance Schema 避免使用互斥锁来收集或生成数据，因此不能保证一致性，结果有时可能不正确。performance_schema 表中的事件值是不确定的且不可重复的。The Performance Schema avoids using mutexes to collect or produce data, so there are no guarantees of consistency and results can sometimes be incorrect. Event values in performance_schema tables are nondeterministic and nonrepeatable.

如果你将事件信息保存到另一个表中，不应假设原始事件稍后仍然可用。例如，如果你从 performance_schema 表中选择事件到临时表中，打算稍后将该临时表与原始表进行连接，可能会没有匹配结果。If you save event information in another table, you should not assume that the original events remain available later. For example, if you select events from a performance_schema table into a temporary table, intending to join that table with the original table later, there might be no matches.

mysqldump 和 BACKUP DATABASE 会忽略 performance_schema 数据库中的表。mysqldump and BACKUP DATABASE ignore tables in the performance_schema database.

Tables in the performance_schema database cannot be locked with LOCK TABLES, except the setup_xxx tables.

performance_schema 数据库中的表不能建立索引。Tables in the performance_schema database cannot be indexed.

performance_schema 数据库中的表不会被复制。Tables in the performance_schema database are not replicated.

计时器的类型可能因平台而异。performance_timers 表显示可用的事件计时器。如果该表中某个计时器名称的值为 NULL，则表示该计时器在您的平台上不受支持。The types of timers might vary per platform. The performance_timers table shows which event timers are available. If the values in this table for a given timer name are NULL, that timer is not supported on your platform.

适用于存储引擎的仪器可能并未在所有存储引擎中实现。各第三方引擎的仪器化由引擎维护者负责。Instruments that apply to storage engines might not be implemented for all storage engines. Instrumentation of each third-party engine is the responsibility of the engine maintainer.