MySQL 8.4 Release Notes
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_digest_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_index_stat_lost | 0 |
| Performance_schema_locker_lost | 0 |
| Performance_schema_memory_classes_lost | 0 |
| Performance_schema_metadata_lock_lost | 0 |
| Performance_schema_meter_lost | 0 |
| Performance_schema_metric_lost | 0 |
| Performance_schema_mutex_classes_lost | 0 |
| Performance_schema_mutex_instances_lost | 0 |
| Performance_schema_nested_statement_lost | 0 |
| Performance_schema_prepared_statements_lost | 0 |
| Performance_schema_program_lost | 0 |
| Performance_schema_rwlock_classes_lost | 0 |
| Performance_schema_rwlock_instances_lost | 0 |
| Performance_schema_session_connect_attrs_longest_seen | 131 |
| Performance_schema_session_connect_attrs_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_table_lock_stat_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 29.7, “Performance Schema Status Monitoring”.
Performance Schema status variables have the following meanings:
Performance_schema_accounts_lostThe number of times a row could not be added to the
accountstable because it was full.Performance_schema_cond_classes_lostHow many condition instruments could not be loaded.
Performance_schema_cond_instances_lostHow many condition instrument instances could not be created.
Performance_schema_digest_lostThe number of digest instances that could not be instrumented in the
events_statements_summary_by_digesttable. This can be nonzero if the value ofperformance_schema_digests_sizeis too small.Performance_schema_file_classes_lostHow many file instruments could not be loaded.
Performance_schema_file_handles_lostHow many file instrument instances could not be opened.
Performance_schema_file_instances_lostHow many file instrument instances could not be created.
The number of times a row could not be added to the
hoststable because it was full.Performance_schema_index_stat_lostThe number of indexes for which statistics were lost. This can be nonzero if the value of
performance_schema_max_index_statis too small.Performance_schema_locker_lostHow 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_lostThe number of times a memory instrument could not be loaded.
Performance_schema_metadata_lock_lostThe number of metadata locks that could not be instrumented in the
metadata_lockstable. This can be nonzero if the value ofperformance_schema_max_metadata_locksis too small.Number of meter instruments that failed to be created.
Performance_schema_metric_lostNumber of metric instruments that failed to be created.
Performance_schema_mutex_classes_lostHow many mutex instruments could not be loaded.
Performance_schema_mutex_instances_lostHow many mutex instrument instances could not be created.
Performance_schema_nested_statement_lostThe number of stored program statements for which statistics were lost. This can be nonzero if the value of
performance_schema_max_statement_stackis too small.Performance_schema_prepared_statements_lostThe number of prepared statements that could not be instrumented in the
prepared_statements_instancestable. This can be nonzero if the value ofperformance_schema_max_prepared_statements_instancesis too small.Performance_schema_program_lostThe number of stored programs for which statistics were lost. This can be nonzero if the value of
performance_schema_max_program_instancesis too small.Performance_schema_rwlock_classes_lostHow many rwlock instruments could not be loaded.
Performance_schema_rwlock_instances_lostHow many rwlock instrument instances could not be created.
Performance_schema_session_connect_attrs_longest_seenIn addition to the connection attribute size-limit check performed by the Performance Schema against the value of the
performance_schema_session_connect_attrs_sizesystem 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 thePerformance_schema_session_connect_attrs_longest_seenstatus variable. If this value is larger thanperformance_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 29.12.9, “Performance Schema Connection Attribute Tables”.
Performance_schema_session_connect_attrs_lostThe 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_sizesystem variable, the Performance Schema truncates the attribute data and incrementsPerformance_schema_session_connect_attrs_lost. If this value is nonzero, you may wish to setperformance_schema_session_connect_attrs_sizeto a larger value.For more information about connection attributes, see Section 29.12.9, “Performance Schema Connection Attribute Tables”.
Performance_schema_socket_classes_lostHow many socket instruments could not be loaded.
Performance_schema_socket_instances_lostHow many socket instrument instances could not be created.
Performance_schema_stage_classes_lostHow many stage instruments could not be loaded.
Performance_schema_statement_classes_lostHow many statement instruments could not be loaded.
Performance_schema_table_handles_lostHow many table instrument instances could not be opened. This can be nonzero if the value of
performance_schema_max_table_handlesis too small.Performance_schema_table_instances_lostHow many table instrument instances could not be created.
Performance_schema_table_lock_stat_lostThe number of tables for which lock statistics were lost. This can be nonzero if the value of
performance_schema_max_table_lock_statis too small.Performance_schema_thread_classes_lostHow many thread instruments could not be loaded.
Performance_schema_thread_instances_lostThe number of thread instances that could not be instrumented in the
threadstable. This can be nonzero if the value ofperformance_schema_max_thread_instancesis too small.The number of times a row could not be added to the
userstable because it was full.