Cache System:
Read:
If data is in cache, it will not be read from the database.
If data is not in cache, it will be read from the database.
Write:
As data is written in permanent storage, applying the cache system is not related with the enhancement of writing performance
IMDG : In Memory Data Grid.
Read : It is always read from IMDG main memory, therefore it's fast
Write : Even when configured to synchronize data to permanent storage some products support non-synchronized write. In this case you can expect a very high write performance.