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
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