Introduction
The MySQL Optimizer sometimes needs a temporary data-store during
query processing, for storing intermediate results. Before
MySQL 5.7, this need was serviced exclusively using a combination
of the HEAP/MEMORY storage engine (for smaller
tables) and the MyISAM storage engine (for larger
tables). You can find more information on when disk based
temporary tables (MyISAM or InnoDB) are used instead of MEMORY
tables here.
The …