inmemory_force = CELLMEMORY_LEVEL

The Oracle Database InMemory feature requires the amount of physical memory from the database server to place IM Cache and some amount CPU resources.

The Exadata has the ability to use InMemory database feature on the cells. To use InMemory feature on cells you should enable the INMEMORY_SIZE at the Database nodes. So, Exadata owners still need to spend the amount of physical memory on the Database servers and memory on the cells.

The 19.8 PSU have brought the new great feature: inmemory_force = CELLMEMORY_LEVEL which offload 100% IM load to the cell level that significantly improve offloading for IM operations.

Starting with PSU 19.8, you can use the CellMemory feature without enabling the IM column store on the DB level. Starting with PSU 19.8 you can use combination of parameters

INMEMORY_FORCE=CELLMEMORY_LEVEL +  INMEMORY_SIZE=0

to enable IM column store at cell level and minimize IM Cache memory consumption at DB level.

From my point of view this feature will greatly improve the scalability of Exadata database machine for IM operations, because the more cells the more physical memory, IM-cache and CPU cores. This feature bring the more value to the Exadata cells.