Performance Schema Summary Tables Each memory summary table has these summary columns containing aggregated values: The aggregated numbers of calls to memory-allocation and memory-free functions. The aggregated sizes of allocated and freed memory blocks. The aggregated number of currently allocated blocks that have not been freed yet. This is a convenience column, equal to  COUNT_ALLOC − COUNT_FREE . The aggregated size of currently allocated memory blocks that have not been freed yet. This is a convenience column, equal to  SUM_NUMBER_OF_BYTES_ALLOC − SUM_NUMBER_OF_BYTES_FREE . The low and high water marks corresponding to the  CURRENT_COUNT_USED  column. The low and high water marks corresponding to the  CURRENT_NUMBER_OF_BYTES_USED  column. The memory summary tables have these indexes: TRUNCATE TABLE  is permitted for memory summary tables. It has these effects: 5071 •Likewise,  SUM_NUMBER_OF_BYTES_ALLOC  and  SUM_NUMBER_OF_BYTES_FREE  are reset to a new baseline. • COUNT_ALLOC  and  COUNT_FREE  are reset to a new baseline, by reducing each counter by the same value. •In general, truncation resets the baseline for statistics, but does not change the server state. That is, truncating a memory table does not free memory. •Primary key on ( EVENT_NAME ) • memory_summary_global_by_event_name : •Primary key on ( USER ,  EVENT_NAME ) • memory_summary_by_user_by_event_name : •Primary key on ( THREAD_ID ,  EVENT_NAME ) • memory_summary_by_thread_by_event_name : •Primary key on ( HOST ,  EVENT_NAME ) • memory_summary_by_host_by_event_name : •Primary key on ( USER ,  HOST ,  EVENT_NAME ) • memory_summary_by_account_by_event_name : • LOW_NUMBER_OF_BYTES_USED ,  HIGH_NUMBER_OF_BYTES_USED • LOW_COUNT_USED ,  HIGH_COUNT_USED • CURRENT_NUMBER_OF_BYTES_USED • CURRENT_COUNT_USED • SUM_NUMBER_OF_BYTES_ALLOC ,  SUM_NUMBER_OF_BYTES_FREE • COUNT_ALLOC ,  COUNT_FREE