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Re: How to uses self query plan

From: "Scott Marlowe" <scott(dot)marlowe(at)gmail(dot)com>
To: "olivier boissard" <olivier(dot)boissard(at)cerene(dot)fr>
Cc: pgsql-admin(at)postgresql(dot)org
Subject: Re: How to uses self query plan
Date: 2007-12-19 15:33:06
Message-ID: dcc563d10712190733n12af01f6tc9ef225e278a04ed@mail.gmail.com (view raw or flat)
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Lists: pgsql-admin
On Dec 19, 2007 1:57 AM, olivier boissard <olivier(dot)boissard(at)cerene(dot)fr> wrote:
> Scott Marlowe a écrit :
>
> > On Dec 18, 2007 4:21 PM, olivier(dot)boissard(at)cerene(dot)fr
> > <olivier(dot)boissard(at)cerene(dot)fr> wrote:
> >
> >> Hello,
> >>
> >> My purpose is to uses different query plan depending on queries
> >> I got the following problem : some queries are taking too much time and
> >> postgresql does not take the most relevant index in account.
> >> I search on internet and found that no HINT function was available in
> >> postgresl.
> >> I tried to change indexes parameters in postgresql.conf but eache time I
> >> set a param to OFF (example nested_loop ,seqscan, ...) , some queries
> >> freeze database .
> >>
> >> How can we force postgresql to use a plan ?
> >>
> >
> > That's not how we do things in postgresql land (usually).
> >
> > You should figure out WHY your queries are picking the wrong plan, and
> > then see if you can get them to pick the right ones.  If it's a query
> > planner bug, you report it here, or the perform or general lists, and
> > it gets fixed.  Generic hints aren't likely to happen any time soon,
> > although I do believe 8.3 is introducing function costing of some
> > kind, which seems like a useful idea.
> >
> > But, back to fixing your slow queries.
> >
> > 1: Increase statistics targets on the guilty columns and reanalyze.
> > 2: Run explain analyze select.... and post the output here.
> > 3: ???
> > 4: profit?
> >
> Thanks for reply
>
> I will extract some queries.
> I want to precise that I use postgresql 8.1.0 .

First step would be to update to the latest 8.1.x version, whatever
that is.  There have been a LOT of fixes in the 8.1 branch since 8.1.0
came out, and one might be a fix for your query problem.  minor
updates are strictly bug and security fixes, so they're not likely to
cause any problems.

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