Are DB hits costlier than accessing collection in java?

Question

Just implemented a design where i had cached some data in hashmap and retrieved data from it instead querying the same data from DB.

Is my thinking correct ?

Answer 1

Keeping a copy of the data in memory would almost certainly be faster than fetching it from the DB.

That said, there are further considerations to be taken into account:

1. Can the data in the DB change while you're holding an in-memory copy? If so, how are you going to deal with that?
2. Is memory consumption going to be an issue?
3. Are you certain that you're optimizing a real, and not an imagined, bottleneck?