Zipf is a little idealistic. It is perfect for a quick analysis as the base case that a cache should excel at. Unfortunately LRU doesn't because it can be easil

Zipf is a little idealistic. It is perfect for a quick analysis as the base case that a cache should excel at. Unfortunately LRU doesn't because it can be easily polluted. (examples: https://github.com/ben-manes/caffeine/wiki/Efficiency https://github.com/ben-manes/caffeine/wiki/Efficiency) A database will often scan many records which would flush an LRU. Postgres uses small LRU buffer caches in your per-thread model, backed by a larger LRU-like cache. The buffer caches are easily flushed by scans, but protect the shared cache from this noise. That shared cache could probably benefit from a smarter policy and this is an on going topic.