Comments - MEMORY Storage Engine

Some findings: The memory for a MEMORY table is only allocated when used. So an empty MEMORY table does nearly not use any space.

Example: 2 MEMORY tables with max_heap_table_size = 64M and fully filled up until: ERROR 1114 (HY000): The table 'test_mem2' is full

select event_name, CURRENT_NUMBER_OF_BYTES_USED 
  from performance_schema.memory_summary_global_by_event_name 
  where event_name like 'memory/memory/%';
+-------------------------+------------------------------+
| event_name              | CURRENT_NUMBER_OF_BYTES_USED |
+-------------------------+------------------------------+
| memory/memory/HP_SHARE  |                         4776 |
| memory/memory/HP_INFO   |                         4000 |
| memory/memory/HP_PTRS   |                    134636384 |
| memory/memory/HP_KEYDEF |                            0 |
+-------------------------+------------------------------+