Re: Question about Bitmap Heap Scan/BitmapAnd

From: "Guillaume Smet" <guillaume(dot)smet(at)gmail(dot)com>
To: "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: "Alvaro Herrera" <alvherre(at)commandprompt(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Question about Bitmap Heap Scan/BitmapAnd
Date: 2007-02-16 00:32:42
Message-ID: 1d4e0c10702151632o3846869rddb0a9f83adfcadd@mail.gmail.com
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On 2/15/07, Guillaume Smet <guillaume(dot)smet(at)gmail(dot)com> wrote:
> On 2/15/07, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> > I think that the
> > answer is probably "because the index is lossy for this operator,
> > so it has to be checked even if the bitmap didn't become lossy".
> > You'd have to check the GIST opclass definition to be sure.

FYI I've taken a look at PostGIS source code and the index is lossy
for the operator &&:
OPERATOR 3 && RECHECK,

(for every operator in the opclass to be exact)

--
Guillaume

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