Re: bitmap-index-scan slower than normal index scan - Mailing list pgsql-performance

From Andreas Kretschmer
Subject Re: bitmap-index-scan slower than normal index scan
Date
Msg-id 20070711201958.GA18449@KanotixBox
Whole thread Raw
In response to Re: bitmap-index-scan slower than normal index scan  (Tom Lane <tgl@sss.pgh.pa.us>)
Responses Re: bitmap-index-scan slower than normal index scan
List pgsql-performance
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°

pgsql-performance by date:

Previous
From: Tom Lane
Date:
Subject: Re: bitmap-index-scan slower than normal index scan
Next
From: Francisco Reyes
Date:
Subject: Re: WALL on controller without battery?