Re: Incorrect information in src/backend/optimizer/README

"Etsuro Fujita" <fujita.etsuro@lab.ntt.co.jp> writes:
> ISTM the README contains incorrect information and requires revision to reflect
> the current code.  Please find attached a patch.  ISTM the patch needs to be
> applied to all active branches.

This patch isn't an improvement, since grouping_planner doesn't have
anything to do with constant quals at all.  In modern releases, that's
dealt with by create_gating_plan inside create_plan().

I remember looking at this text when I redid query_planner's API a few
days ago and electing not to change it just then.  I'm a bit inclined to
just remove both references to constant quals from this overview, since
they're now taken care of at much lower levels --- query_planner itself
has nothing to do with that processing.  Alternatively, if we do want to
discuss constant quals somewhere in here, maybe it needs to be in a
separate subsection.  I'm not sure we need anything though.  Constant
quals are now handled just like other quals up till the last moment in
createplan.c, where they're split out and put in a separate gating
Result node just above where they would otherwise have been.
        regards, tom lane