| From: | Peter Geoghegan <pg(at)bowt(dot)ie> |
|---|---|
| To: | pgsql-hackers(at)lists(dot)postgresql(dot)org |
| Cc: | hlinnaka(at)iki(dot)fi, Matthias van de Meent <boekewurm+postgres(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Andres Freund <andres(at)anarazel(dot)de>, Tomas Vondra <tomas(at)vondra(dot)me> |
| Subject: | Re: Why doesn't GiST VACUUM require a super-exclusive lock, like nbtree VACUUM? |
| Date: | 2024-12-03 16:21:04 |
| Message-ID: | CAH2-WzkCSdOKOHfRX3irGfN1R_qig8eLi-tRrCFuain5RuNZUA@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Mon, Dec 2, 2024 at 8:18 PM Peter Geoghegan <pg(at)bowt(dot)ie> wrote:
> Attached is a refined version of a test case I posted earlier on [2],
> decisively proving that GiST index-only scans are in fact subtly
> broken. Right now it fails, showing a wrong answer to a query. The
> patch adds an isolationtest test case to btree_gist, based on a test
> case of Andres'.
I can confirm that the same bug affects SP-GiST. I modified the
original failing GiST isolation test to make it use SP-GiST instead,
proving what I already strongly suspected.
I have no reason to believe that there are any similar problems in
core index AMs other than GiST and SP-GiST, though. Let's go through
them all now: nbtree already does everything correctly, and all
remaining core index AMs don't support index-only scans *and* don't
support scans that don't just use an MVCC snapshot.
--
Peter Geoghegan
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