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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: pgsql-performance(at)postgresql(dot)org
Subject: Re: Question about Bitmap Heap Scan/BitmapAnd
Date: 2007-02-13 17:17:41
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
On 2/13/07, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>     bitmapqualorig = list_difference_ptr(bitmapqualorig, qpqual);
> What's not immediately clear is why the condition was in both lists to
> start with.  Perhaps idx_lieu_parking is a partial index with this as
> its WHERE condition?

Yes, it is: "idx_lieu_parking" btree (parking) WHERE parking = true .
Sorry for not pointing it immediatly.
If not, the index is not used at all (there are very few lines in lieu
with parking=true).

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?

Thanks for your answer.


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