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Re: bad estimates

From: Sean Chittenden <sean(at)chittenden(dot)org>
To: Ken Geis <kgeis(at)speakeasy(dot)org>
Cc: Bruno Wolff III <bruno(at)wolff(dot)to>,pgsql-performance(at)postgresql(dot)org
Subject: Re: bad estimates
Date: 2003-08-29 16:36:13
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Lists: pgsql-performance
> >If you want both the max and the min, then things are going to be a
> >bit more work. You are either going to want to do two separate
> >selects or join two selects or use subselects. If there aren't
> >enough prices per stock, the sequential scan might be fastest since
> >you only need to go through the table once and don't have to hit
> >the index blocks.
> >
> >It is still odd that you didn't get a big speed up for just the min though.
> I found I'm suffering from an effect detailed in a previous thread titled
> 	Does "correlation" mislead the optimizer on large tables?

I don't know about large tables, but this is a big problem and
something I'm going to spend some time validating later today.  I
think Manfred's patch is pretty good and certainly better than where
we are but I haven't used it yet to see if it's the magic ticket for
many of these index problems.


Sean Chittenden

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