20.13. 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_accounts_lost          | 0     || 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_hosts_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_socket_classes_lost    | 0     || Performance_schema_socket_instances_lost  | 0     || Performance_schema_stage_classes_lost     | 0     || Performance_schema_statement_classes_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_users_lost             | 0     |+-------------------------------------------+-------+

Names for these variables have several forms:

Performance_schema_accounts_lost

The number of times a row could not be added to the accounts table because it was full.
Performance_schema_xxx_classes_lost

How many instruments of type xxx could not be loaded.
Performance_schema_hosts_lost

The number of times a row could not be added to the hosts table because it was full.
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 the Performance Schema are not recursive, so this variable should always be 0.
Performance_schema_session_connect_attrs_lost

The number of times a connection attribute string was larger than the reserved storage.
Performance_schema_users_lost

The number of times a row could not be added to the users table because it was full.

For information on using these variables to check Performance Schema status, see Section 20.5, "Performance Schema Status Monitoring".