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.

If you save event information in another table, you should not assume that the original events are still 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 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.

Tables in the performance_schema database cannot be indexed.

Results for queries that refer to tables in the performance_schema database are not saved in the query cache.

Tables in the performance_schema database are not replicated.

The Performance Schema is not available in libmysqld, the embedded server.

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.

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.