On May 15, 2006, at 21:31, Tom Lane wrote:
Sure. As I read it, that's talking about a static transformation: planner sees 2 + 2 (or if you prefer, int4pl(2,2)), planner runs the function and replaces the expression with 4. Nothing there about memoization.
Oh, I see. So it's more like a constant or C macro.
It's true that the system *could* memoize (or in our more usual parlance, cache function values) given the assumptions embodied in IMMUTABLE. But we don't, and I don't see any statement in the docs that promises that we do. For 99% of the functions that the planner deals with, memoization would be seriously counterproductive because the function evaluation cost is comparable to if not less than the lookup cost in a memo table. (int4pl is a good case in point.)
Yes, but there are definitely programming cases where memoization/ caching definitely helps. And it's easy to tell for a given function whether or not it really helps by simply trying it with CACHED and without.
Would this be a simple thing to implement? Best, David
