Magento 2. Declarative schema. What is the use of the memory engine?

Question

When creating tables using the Declarative Schema one can set the engine="" attribute value as memory.

I can't seem to find an example in the core. What is a use-case for this configuration, how does it behave and how you retrieve|store values in|from such a table?

Reference M2 Dev Docs

Answer 1

Currently Magento2 uses InnoDb engine but this configuration for Memory engine if you want to configure it.

in core all most of tmp table created with memory engine:

catalog_product_index_price_opt_tmp

catalog_product_index_price_final_tmp

catalog_product_index_price_cfg_opt_agr_tmp

catalog_product_index_price_cfg_opt_tmp

catalog_product_index_price_opt_agr_tmp

catalog_product_index_eav_tmp

catalog_product_index_eav_decimal_tmp

catalog_product_index_price_tmp

cataloginventory_stock_status_tmp

and some more tables....

for more please see

https://dev.mysql.com/doc/refman/8.0/en/memory-storage-engine.html