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From: Kirill Reshke <reshkekirill@gmail.com>
Date: Thu, 15 Jan 2026 22:59:31 +0500
Message-ID: <CALdSSPgfFWUBc8RoOZe5PmoUGa4LJUDeMTcAT8HwXGCMGJ9uBA@mail.gmail.com>
Subject: Re: Fix gistkillitems & add regression test to microvacuum
To: pgsql-hackers <pgsql-hackers@postgresql.org>
Content-Type: multipart/mixed; boundary="000000000000520b04064870fd45"
Archived-At: <https://www.postgresql.org/message-id/CALdSSPgfFWUBc8RoOZe5PmoUGa4LJUDeMTcAT8HwXGCMGJ9uBA%40mail.gmail.com>
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On Thu, 15 Jan 2026 at 13:35, Kirill Reshke <reshkekirill@gmail.com> wrote:
>
> On Thu, 15 Jan 2026 at 13:21, Kirill Reshke <reshkekirill@gmail.com> wrote:
> >
> > 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
>
> I was right on commit message of 377b7ab
>
> """
> For gist some related paths were reached, but gist's implementation
> seems to not work if all the dead tuples are on one page (or something
> like that). The coverage for other index types was rather incidental.
> """
>
> It does not work  if all the dead tuples are on one page and this page is ROOT.
>
> So, should we delete this
>
> ...
> # Test gist, but with fewer rows - shows that killitems doesn't work anymore!
> permutation
>   create_table fill_10 create_ext_btree_gist create_gist flush
>   disable_seq disable_bitmap
>
> ...
>
>  from isolation spec?
>
>
> --
> Best regards,
> Kirill Reshke

PFA v2 which leaves the test in-place.

Also commit message improvements.

-- 
Best regards,
Kirill Reshke

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