Re: Call for objections: simplify stable functions
От | Simon Riggs |
---|---|
Тема | Re: Call for objections: simplify stable functions |
Дата | |
Msg-id | 1100021294.4442.152.camel@localhost.localdomain обсуждение исходный текст |
Ответ на | Call for objections: simplify stable functions during estimation (Tom Lane <tgl@sss.pgh.pa.us>) |
Список | pgsql-hackers |
On Tue, 2004-11-09 at 16:28, 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? None. IMHO Poor performance is a valid bug that must be addressed in the beta cycle. We've chased out most of the functional deficiencies, now its time to concentrate on the performance ones. -- Best Regards, Simon Riggs
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