From: Andreas Kretschmer <akretschmer@spamfence.net>
To: pgsql-performance@postgresql.org
Subject: Re: bitmap-index-scan slower than normal index scan
Date: Wed, 11 Jul 2007 22:19:58 +0200
Message-ID: <20070711201958.GA18449@KanotixBox> (raw)
In-Reply-To: <1331.1184184273@sss.pgh.pa.us>
References: <20070711183638.GA30872@KanotixBox>
<1331.1184184273@sss.pgh.pa.us>
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
--
Really, I'm not out to destroy Microsoft. That will just be a completely
unintentional side effect. (Linus Torvalds)
"If I was god, I would recompile penguin with --enable-fly." (unknow)
Kaufbach, Saxony, Germany, Europe. N 51.05082°, E 13.56889°
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To: pgsql-performance@postgresql.org
Cc: akretschmer@spamfence.net
Subject: Re: bitmap-index-scan slower than normal index scan
In-Reply-To: <20070711201958.GA18449@KanotixBox>
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