On Sat, Feb 27, 2010 at 11:22 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: > Robert Haas <robertmh...@gmail.com> writes: >> On Fri, Feb 26, 2010 at 7:03 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: >>> Wouldn't it be better if it just did the right thing automatically? >>> >>> The sort of heuristic I'm envisioning would essentially do "replan every >>> time" for some number of executions, and give up only if it noticed that >>> it wasn't getting anything better than the generic plan. So you'd have >>> a fixed maximum overhead per session when the custom plan was useless, >>> and the Right Thing when it wasn't. > >> Which is likely useless for my use case. > > [ shrug... ] You'd better explain exactly why, if you want me to take > that objection seriously.
Hmm... on further thought, maybe it *would* work in that case. I'm still not convinced this is going to be generally satisfactory. It seems like it depends a great deal on how many times the function figures to be called per session and in what percentage of those cases a non-generic plan figures to be better. The appeal of a user-controllable knob is that I am pretty sure from experience that I can set it correctly, but hey... ...Robert -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
