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Re: How to uses self query plan

From: olivier boissard <olivier(dot)boissard(at)cerene(dot)fr>
To: Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>
Cc: pgsql-admin(at)postgresql(dot)org
Subject: Re: How to uses self query plan
Date: 2007-12-19 07:57:35
Message-ID: 4768CEEF.9060506@cerene.fr (view raw or flat)
Thread:
Lists: pgsql-admin
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?
>
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>   
Thanks for reply

I will extract some queries.
I want to precise that I use postgresql 8.1.0 .

Olivier



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