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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 inperformance_schema tables are nondeterministic and nonrepeatable.

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 aperformance_schema table into a temporary table, intending to join that table with the original table later, there might be no matches.

mysqldump andBACKUP DATABASE ignore tables in theperformance_schema database.

Tables in theperformance_schema database cannot be locked withLOCK TABLES, except thesetup_xxx tables.

Tables in theperformance_schema database cannot be indexed.

Tables in theperformance_schema database are not replicated.

The types of timers might vary per platform. Theperformance_timers table shows which event timers are available. If the values in this table for a given timer name areNULL, 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.