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MySQL 5.5 Reference Manual :: 20 MySQL Performance Schema :: 20.10 Performance Schema Status Variables
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20.10. Performance Schema Status Variables

Performance Schema implements several status variables that provide information about instrumentation that could not be loaded or created due to memory constraints: 

mysql> SHOW STATUS LIKE 'perf%';
+------------------------------------------+-------+
| Variable_name                            | Value |
+------------------------------------------+-------+
| Performance_schema_cond_classes_lost     | 0     |
| Performance_schema_cond_instances_lost   | 0     |
| Performance_schema_file_classes_lost     | 0     |
| Performance_schema_file_handles_lost     | 0     |
| Performance_schema_file_instances_lost   | 0     |
| Performance_schema_locker_lost           | 0     |
| Performance_schema_mutex_classes_lost    | 0     |
| Performance_schema_mutex_instances_lost  | 0     |
| Performance_schema_rwlock_classes_lost   | 0     |
| Performance_schema_rwlock_instances_lost | 0     |
| Performance_schema_table_handles_lost    | 0     |
| Performance_schema_table_instances_lost  | 0     |
| Performance_schema_thread_classes_lost   | 0     |
| Performance_schema_thread_instances_lost | 0     |
+------------------------------------------+-------+

Names for these variables have several forms:

  • Performance_schema_xxx_classes_lost

    How many instruments of type xxx could not be loaded.

  • Performance_schema_xxx_instances_lost

    How many instances of object type xxx could not be created.

  • Performance_schema_xxx_handles_lost

    How many instances of object type xxx could not be opened.

  • Performance_schema_locker_lost

    How many events are “lost” or not recorded, due to the following conditions:

    • Events are recursive (for example, waiting for A caused a wait on B, which caused a wait on C).

    • The depth of the nested events stack is greater than the limit imposed by the implementation.

    Currently, events recorded by Performance Schema are not recursive, so that this variable should always be 0.

For information on using these variables to check Performance Schema status, see Section 20.3, “Performance Schema Status Monitoring”.