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Re: Question about Bitmap Heap Scan/BitmapAnd

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Alvaro Herrera <alvherre(at)commandprompt(dot)com>
Cc: Guillaume Smet <guillaume(dot)smet(at)gmail(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Question about Bitmap Heap Scan/BitmapAnd
Date: 2007-02-15 16:34:49
Message-ID: 26633.1171557289@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-performance
Alvaro Herrera <alvherre(at)commandprompt(dot)com> writes:
> Guillaume Smet escribi:
>> Is it normal I have no recheck cond and the index cond of Bitmap Index
>> Scan is in the filter? Is it also a consequence of the code you
>> pointed?

> It is in the filter, is it not?  Having a recheck would be redundant.

Yeah, but his question is why is it in the filter?  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.

			regards, tom lane

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