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Re: Question about Bitmap Heap Scan/BitmapAnd

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "Guillaume Smet" <guillaume(dot)smet(at)gmail(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: Question about Bitmap Heap Scan/BitmapAnd
Date: 2007-02-13 17:51:05
Message-ID: 1977.1171389065@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-performance
"Guillaume Smet" <guillaume(dot)smet(at)gmail(dot)com> writes:
> So the basic explanation is that it's in both lists due to the partial
> index and only qpqual keeps the condition? I would have expected the
> opposite but it doesn't change anything I suppose?

It gets the right answer, yes.  I'm not sure if we could safely put the
condition into the recheck instead of the filter.  The particular code
I showed you has to go the direction it does, because a condition in the
filter has to be checked even if the bitmap is not lossy.  I seem to
recall concluding that we had to recheck partial-index conditions even
if the bitmap is not lossy, but I can't reconstruct my reasoning at the
moment.

			regards, tom lane

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