Re: Question about Bitmap Heap Scan/BitmapAnd - Mailing list pgsql-performance

From Tom Lane
Subject Re: Question about Bitmap Heap Scan/BitmapAnd
Date
Msg-id 26633.1171557289@sss.pgh.pa.us
Whole thread Raw
In response to Re: Question about Bitmap Heap Scan/BitmapAnd  (Alvaro Herrera <alvherre@commandprompt.com>)
Responses Re: Question about Bitmap Heap Scan/BitmapAnd  ("Guillaume Smet" <guillaume.smet@gmail.com>)
List pgsql-performance
Alvaro Herrera <alvherre@commandprompt.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

pgsql-performance by date:

Previous
From: Alvaro Herrera
Date:
Subject: Re: Question about Bitmap Heap Scan/BitmapAnd
Next
From: philippe
Date:
Subject: Re: Slow query with 'or' clause