Re: Immutable function WAY slower than Stable function?

> On Aug 7, 2018, at 11:42, Ken Tanzer <ken(dot)tanzer(at)gmail(dot)com> wrote:
> I assume that's "for all users and all sessions," but either in theory or in practice is there a limit to how long a stale value might persist? And, if you were to drop and recreate a function with the same name & parameters, would it start fresh at that point? And is there a way to flush any caching? (It's surely best to just declare Stable, but I'm wondering about cases that might have _very_ infrequently-changed values.)

Well, the extreme case is an IMMUTABLE function used to create an expression index; then, the value lasts as long as the index does. The best way to think of an IMMUTABLE is that it is a pure function, unchanged by system state. (This is one of the reasons that datetime-related functions are often STABLE rather than IMMUTABLE, due to time zone changes.)

--
-- Christophe Pettus
xof(at)thebuild(dot)com