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MySQL 5.5 Reference Manual  /  MySQL Performance Schema  /  Performance Schema Status Variables

22.10 Performance Schema Status Variables

The 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     |
+------------------------------------------+-------+

Performance Schema status variables have the following meanings:

  • Performance_schema_cond_classes_lost

    How many condition instruments could not be loaded.

  • Performance_schema_cond_instances_lost

    How many condition instrument instances could not be created.

  • Performance_schema_file_classes_lost

    How many file instruments could not be loaded.

  • Performance_schema_file_handles_lost

    How many file instrument instances could not be opened.

  • Performance_schema_file_instances_lost

    How many file instrument instances could not be created.

  • 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.

    Events recorded by the Performance Schema are not recursive, so this variable should always be 0.

  • Performance_schema_mutex_classes_lost

    How many mutex instruments could not be loaded.

  • Performance_schema_mutex_instances_lost

    How many mutex instrument instances could not be created.

  • Performance_schema_rwlock_classes_lost

    How many rwlock instruments could not be loaded.

  • Performance_schema_rwlock_instances_lost

    How many rwlock instrument instances could not be created.

  • Performance_schema_table_handles_lost

    How many table instrument instances could not be opened.

  • Performance_schema_table_instances_lost

    How many table instrument instances could not be created.

  • Performance_schema_thread_classes_lost

    How many thread instruments could not be loaded.

  • Performance_schema_thread_instances_lost

    The number of thread instances that could not be instrumented in the threads table. This can be nonzero if the value of performance_schema_max_thread_instances is too small.

For information on using these variables to check Performance Schema status, see Section 22.5, “Performance Schema Status Monitoring”.


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