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From: Kirill Reshke <reshkekirill@gmail.com>
Date: Thu, 15 Jan 2026 13:21:51 +0500
Message-ID: <CALdSSPiaQptrccvRoHhP3=YqN9-K8duXfLHHm3G=+7FVL8A-Xw@mail.gmail.com>
Subject: Re: Fix gistkillitems & add regression test to microvacuum
To: pgsql-hackers <pgsql-hackers@postgresql.org>
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On Thu, 15 Jan 2026 at 12:46, Kirill Reshke <reshkekirill@gmail.com> wrote:
>
> On Thu, 15 Jan 2026 at 12:00, Kirill Reshke <reshkekirill@gmail.com> wrote:
> >
> > Hi hackers.
> >
> > While looking at [0] I noticed that XLOG_GIST_DELETE &  XLOG_GIST_PAGE_DELETE
> > records are not covered.
> >
> > This thread addresses XLOG_GIST_DELETE, which is also known as a
> > microvacuum feature.
> >
> > test.sql contains regression test that trigger this code to be
> > exercised in stream_regress.pl TAP test.
> >
> > Test is as follows: we create a gist index on the table, then we
> > insert exactly 407 records, making the root page full (next insert
> > will trigger page split). Then I delete all tuples from relation and
> > trigger Index Only scan to do kill-on-select (killtuples). It marks
> > gist 0 page (which is root and is leaf) as has_garbage. Then, the next
> > insertion triggers xlog_gist_delete record.
> >
> > To verify this I use pageinspect and pg_waldimp (locally). Also this
> > test is dependent on block size being 8192 which is not good.
> >
> >
> > And all of this does not work actually without v1-0001, because there
> > is a bug in GiST which does not call gistkillitmes for the very first
> > (root) page.
> >
> > There is also test2.sql which inserts a single tuple, not 407. It can
> > be used to verify v1-0001.
> >
> > [0] coverage.postgresql.org/src/backend/access/gist/gistxlog.c.gcov.html
> >
> >
> > --
> > Best regards,
> > Kirill Reshke
>
>
> From cf feedback it turns out we already have an isolation test for
> this, and it does almost exactly the same.
> And more, it fails.
> Will try to fix
>
>
> --
> Best regards,
> Kirill Reshke

This looks like gist does not work for small  indexes and this is
explicitly tested after [0]
[0] https://www.postgresql.org/message-id/lxzj26ga6ippdeunz6kuncectr5gfuugmm2ry22qu6hcx6oid6%40lzx3sjsqhmt6


-- 
Best regards,
Kirill Reshke