Date: Wed, 11 Jul 2007 22:19:58 +0200
From: Andreas Kretschmer <akretschmer@spamfence.net>
To: pgsql-performance@postgresql.org
Subject: Re: bitmap-index-scan slower than normal index scan
Message-ID: <20070711201958.GA18449@KanotixBox>
References: <20070711183638.GA30872@KanotixBox>
 <1331.1184184273@sss.pgh.pa.us>
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Tom Lane <tgl@sss.pgh.pa.us> schrieb:


Thanks you and Alex for the response.

> > PostgreSQL 8.1.4 on i386-pc-linux-gnu, compiled by GCC cc (GCC) 3.3.5 (Debian 1:3.3.5-13)
> 
> You need a newer one.

I know ;-)

> 
> This is simply a stupid choice on the part of choose_bitmap_and() ---
> it's adding on a second index to try to filter on maschine when that
> scan will actually just increase the cost.
> 
> I've revisited choose_bitmap_and() a couple times since then; try
> 8.1.9 and see if it gets this right.

Okay, but later.

> 
> Also, part of the problem here looks to be an overestimate of the number
> of rows matching ab = 347735.  It might help to increase the statistics
> target for that column.

I will try this tomorrow and inform you about the result. I've never
done this before, i need to read the docs about this.

Thank you again.


Andreas
-- 
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