I want to have a memory cache layer in my application. To populate cache with items, I have to get data from a large Cassandra table. Select all is not recommended, because without using partition keys, it's a slow read operation. Prior to that I can "predict" partition keys using other Cassandra table that I'll have to read all again, but relatively it's a smaller volume table. After reading data from user table and creating a list of potential partition keys (userX, userY) that may or may not be present in initial table. With that list try and populate cache by executing select queries with each potential key. That also doesn't sound like a really good idea.
So the question is? How to properly populate cache layer with data from Cassandra DB?