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Re: Idea how to get rid of Bitmap Heap Scan

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Greg Stark <gsstark(at)mit(dot)edu>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, "Michael N(dot) Mikhulya" <m(dot)mikhulya(at)gmail(dot)com>, Matthew Wakeling <matthew(at)flymine(dot)org>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Idea how to get rid of Bitmap Heap Scan
Date: 2009-12-20 16:26:38
Message-ID: 29932.1261326398@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-performance
Greg Stark <gsstark(at)mit(dot)edu> writes:
> In the original poster's plan that isn't an issue. We could scan the
> index, perform the joins and restriction clauses, and only check the
> visibility on the resulting tuples which slip through them all. That
> would be possible even without crash-safe visibility bits.

Yeah, this was floated years ago as being a potentially interesting
approach when all the join-condition fields are indexed.  You end up
never having to fetch rows that don't pass the join.

It certainly seems reasonably straightforward on the executor side.
As Greg said, the hard part is planning it sanely.

			regards, tom lane

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Subject: Re: Idea how to get rid of Bitmap Heap Scan
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