Performance Schema Setup Tables Instruments with a low volatility index (PERMANENT = 1) are created once at server startup, and never destroyed or re-created during normal server operation. They are destroyed only during server shutdown. For example, the  wait/synch/mutex/pfs/LOCK_pfs_share_list  mutex is defined with a volatility of 1, which means it is created once. Possible overhead from the instrumentation itself (namely, mutex initialization) has no effect for this instrument then. Runtime overhead occurs only when locking or unlocking the mutex. Instruments with a higher volatility index (for example, SESSION = 5) are created and destroyed for every user session. For example, the  wait/synch/mutex/sql/THD::LOCK_query_plan  mutex is created each time a session connects, and destroyed when the session disconnects. This mutex is more sensitive to Performance Schema overhead, because overhead comes not only from the lock and unlock instrumentation, but also from mutex create and destroy instrumentation, which is executed more often. Another aspect of volatility concerns whether and when an update to the  ENABLED  column actually has some effect: For example, this statement does not affect the  LOCK_query_plan  mutex for existing sessions, but does have an effect on new sessions created subsequent to the update: This statement actually has no effect at all: This mutex is permanent, and was created already before the update is executed. The mutex is never created again, so the  ENABLED  value in  setup_instruments  is never used. To enable or disable this mutex, use the  mutex_instances  table instead. A string describing the instrument purpose. The value is  NULL  if no description is available. The  setup_objects  table controls whether the Performance Schema monitors particular objects. This table has a maximum size of 100 rows by default. To change the table size, modify the performance_schema_setup_objects_size  system variable at server startup. 27.12.2.4 The setup_objects Table TRUNCATE TABLE  is not permitted for the  setup_instruments  table. 4949 The  setup_instruments  table has these indexes: •Primary key on ( NAME ) • DOCUMENTATION •An update to  ENABLED  affects instrumented objects created subsequently, but has no effect on instruments already created. •Instruments that are more “volatile”  use new settings from the  setup_instruments  table sooner. UPDATE performance_schema.setup_instruments SET ENABLED= value WHERE NAME = ’wait/synch/mutex/sql/THD::LOCK_query_plan’; UPDATE performance_schema.setup_instruments SET ENABLED= value WHERE NAME = ’wait/synch/mutex/pfs/LOCK_pfs_share_list’;