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Re: Fwd: Help with view performance problem

From: Dan Harris <fbsd(at)drivefaster(dot)net>
To: pgsql-performance(at)postgresql(dot)org
Subject: Re: Fwd: Help with view performance problem
Date: 2005-07-28 16:14:32
Message-ID: B0A387FA-9B74-4DB9-9C9F-C8291965A55F@drivefaster.net (view raw or flat)
Thread:
Lists: pgsql-adminpgsql-performance
On Jul 28, 2005, at 8:38 AM, Chris Hoover wrote:
>
>
> I did some more testing, and ran the explain analyze on the problem.
> In my session I did a set enable_hashjoin = false and then ran the
> analyze.  This caused it to use the indexes as I have been expecting
> it to do.
>
> Now, how can I get it to use the indexes w/o manipulating the
> environment?  What make postgresql want to sequentially scan and use a
> hash join?
>
> thanks,
>
> Chris
>
> explain analyze with set_hashjoin=false;
> prob_db=#explain analyze select * from clm_com;
>
>

I had something similar to this happen recently.  The planner was  
choosing a merge join and seq scan because my 'random_page_cost' was  
set too high.  I had it at 3 , and ended up settling at 1.8 to get it  
to correctly use my indices.  Once that change was in place, the  
planner did the 'right' thing for me.

Not sure if this will help you, but it sounds similar.

-Dan

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