On: Internals of PostgreSQL

[anarazel]

That really depends on what you're caching. Sometimes e.g. you might want to have local caches on application servers, not because the database would be too slow or couldn't take the load, but because the roundtrip time to the database make page loads too slow if you hit the DB every time.

Or you have some complex ranking/relationship/aggregation calculations - it might computationally be infeasible for the database, as hard as people worked on its efficiency, to calculate such a query on each request...