Horton

Re: Incorrect result of bitmap heap scan.

Peter Geoghegan <pg@bowt.ie>

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From: Peter Geoghegan <pg@bowt.ie>
To: Andres Freund <andres@anarazel.de>
Cc: Matthias van de Meent <boekewurm+postgres@gmail.com>, Andrew Dunstan <andrew@dunslane.net>, Melanie Plageman <melanieplageman@gmail.com>, Thomas Munro <thomas.munro@gmail.com>, Konstantin Knizhnik <knizhnik@garret.ru>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>, Alexander Kuzmenkov <akuzmenkov@timescale.com>, Tom Lane <tgl@sss.pgh.pa.us>, Heikki Linnakangas <hlinnaka@iki.fi>
Date: 2024-12-02T20:59:36Z
Lists: pgsql-hackers 
On Mon, Dec 2, 2024 at 3:56 PM Peter Geoghegan <pg@bowt.ie> wrote:
> I took what you wrote, and repurposed it to prove my old theory about
> GiST index-only scans being broken due to the lack of an appropriate
> interlock against concurrent TID recycling. See the attached patch.

BTW, if you change the test case to use the default B-Tree index AM
(by removing "USING GIST"), you'll see that VACUUM blocks on acquiring
a cleanup lock (and so the test just times out). The problem is that
GiST VACUUM just doesn't care about cleanup locks/TID recycling safety
-- though clearly it should.

-- 
Peter Geoghegan

Commits

  1. Add test for HeapBitmapScan's broken skip_fetch optimization

  2. Remove HeapBitmapScan's skip_fetch optimization

  3. Allow bitmap scans to operate as index-only scans when possible.