On Tue, 9 Nov 2004, Tom Lane wrote:
> Awhile back, there was some discussion about pre-folding now() and
> related functions when the planner is trying to estimate selectivities.
> This would allow reasonable plans to be made for cases like
> WHERE moddate >= current_date - 10;
> without having to indulge in any crude hacks with mislabeled wrapper
> functions, such as you can find all too often in the archives :-(
>
> I was a bit hesitant about it at the time because I wasn't sure of all
> the implications; but I've looked the idea over again, and as far as I
> can see it's reasonable to pre-fold *all* stable functions when deriving
> statistical estimates. (One of the potential objections went away when
> we started enforcing that stable functions don't have side-effects.)
>
> The infrastructure for this is already there, because of Oliver Jowett's
> previous work to teach eval_const_expressions() whether it's folding
> the expression "for real" or just for estimation; it's basically a one
> line change to treat stable functions differently in the two cases.
>
> I know it's a bit late in the cycle, but I'd like to go ahead and make
> this change for 8.0. Objections?
From a performance tuning standpoing, I can't argue against it ... go for
it ...
----
Marc G. Fournier Hub.Org Networking Services (http://www.hub.org)
Email: scrappy@hub.org Yahoo!: yscrappy ICQ: 7615664
