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Re: Avoiding bad prepared-statement plans.

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Mark Mielke <mark(at)mark(dot)mielke(dot)cc>
Cc: Jeroen Vermeulen <jtv(at)xs4all(dot)nl>, Alex Hunsaker <badalex(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Greg Stark <gsstark(at)mit(dot)edu>, Bart Samwel <bart(at)samwel(dot)tk>, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Avoiding bad prepared-statement plans.
Date: 2010-02-26 18:59:22
Message-ID: 2060.1267210762@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Mark Mielke <mark(at)mark(dot)mielke(dot)cc> writes:
> Just to point out that I agree, and as per my original post, I think the 
> only time prepared statements should be re-planned for the statistics 
> case, is after 'analyze' has run. That sounds like a quicker solution, 
> and a much smaller gain. After 'analyze' of an object, invalidate all 
> cached plans for prepared statements that rely on that object and 
> require a re-plan.

Please note that that has been happening since 8.3, which is probably
why you haven't detected a problem.

> ... It's walking around the problem 
> that the idea of a generic plan is just wrong. The only time a generic 
> plan is right, is when the specific plan would result in the same.

I think that's a significant overstatement.  There are a large number
of cases where a custom plan isn't worth it, even if it doesn't generate
exactly the same plan.

			regards, tom lane

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