• 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. 

## 27.17 The Performance Schema Memory-Allocation Model 

The Performance Schema uses this memory allocation model: 

•May allocate memory at server startup 

•May allocate additional memory during server operation 

•Never free memory during server operation (although it might be recycled) 

•Free all memory used at shutdown 

The result is to relax memory constraints so that the Performance Schema can be used with less configuration, and to decrease the memory footprint so that consumption scales with server load. Memory used depends on the load actually seen, not the load estimated or explicitly configured for. 

Several Performance Schema sizing parameters are autoscaled and need not be configured explicitly unless you want to establish an explicit limit on memory allocation: 

performance_schema_accounts_size performance_schema_hosts_size performance_schema_max_cond_instances performance_schema_max_file_instances performance_schema_max_index_stat performance_schema_max_metadata_locks performance_schema_max_mutex_instances performance_schema_max_prepared_statements_instances performance_schema_max_program_instances 

