27.16 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     |
+-------------------------------------------+-------+

For information on using these variables to check Performance Schema status, see Section 27.7, “Performance Schema Status Monitoring”.

Performance Schema status variables have the following meanings:

• Performance_schema_accounts_lost

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

• 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_digest_lost

  The number of digest instances that could not be instrumented in the events_statements_summary_by_digest table. This can be nonzero if the value of performance_schema_digests_size is too small.

• 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_hosts_lost

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

• Performance_schema_index_stat_lost

  The number of indexes for which statistics were lost. This can be nonzero if the value of performance_schema_max_index_stat is too small.

• 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_memory_classes_lost

  The number of times a memory instrument could not be loaded.

• Performance_schema_metadata_lock_lost

  The number of metadata locks that could not be instrumented in the metadata_locks table. This can be nonzero if the value of performance_schema_max_metadata_locks is too small.

• 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_nested_statement_lost

  The number of stored program statements for which statistics were lost. This can be nonzero if the value of performance_schema_max_statement_stack is too small.

• Performance_schema_prepared_statements_lost

  The number of prepared statements that could not be instrumented in the prepared_statements_instances table. This can be nonzero if the value of performance_schema_max_prepared_statements_instances is too small.

• Performance_schema_program_lost

  The number of stored programs for which statistics were lost. This can be nonzero if the value of performance_schema_max_program_instances is too small.

• 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_session_connect_attrs_longest_seen

  In addition to the connection attribute size-limit check performed by the Performance Schema against the value of the performance_schema_session_connect_attrs_size system variable, the server performs a preliminary check, imposing a limit of 64KB on the aggregate size of connection attribute data it accepts. If a client attempts to send more than 64KB of attribute data, the server rejects the connection. Otherwise, the server considers the attribute buffer valid and tracks the size of the longest such buffer in the Performance_schema_session_connect_attrs_longest_seen status variable. If this value is larger than performance_schema_session_connect_attrs_size, DBAs may wish to increase the latter value, or, alternatively, investigate which clients are sending large amounts of attribute data.

  For more information about connection attributes, see Section 27.12.9, “Performance Schema Connection Attribute Tables”.

• Performance_schema_session_connect_attrs_lost

  The number of connections for which connection attribute truncation has occurred. For a given connection, if the client sends connection attribute key-value pairs for which the aggregate size is larger than the reserved storage permitted by the value of the performance_schema_session_connect_attrs_size system variable, the Performance Schema truncates the attribute data and increments Performance_schema_session_connect_attrs_lost. If this value is nonzero, you may wish to set performance_schema_session_connect_attrs_size to a larger value.

  For more information about connection attributes, see Section 27.12.9, “Performance Schema Connection Attribute Tables”.

• Performance_schema_socket_classes_lost

  How many socket instruments could not be loaded.

• Performance_schema_socket_instances_lost

  How many socket instrument instances could not be created.

• Performance_schema_stage_classes_lost

  How many stage instruments could not be loaded.

• Performance_schema_statement_classes_lost

  How many statement instruments could not be loaded.

• Performance_schema_table_handles_lost

  How many table instrument instances could not be opened. This can be nonzero if the value of performance_schema_max_table_handles is too small.

• Performance_schema_table_instances_lost

  How many table instrument instances could not be created.

• Performance_schema_table_lock_stat_lost

  The number of tables for which lock statistics were lost. This can be nonzero if the value of performance_schema_max_table_lock_stat is too small.

• 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.

• Performance_schema_users_lost

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