Subject: Fix gistkillitems & add regression test to microvacuum

From: Kirill Reshke <[email-masked]>
Date: Thu, 15 Jan 2026 12:00:38 +0500

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: Kirill Reshke <[email-masked]>
Date: Thu, 15 Jan 2026 12:46:44 +0500

---

From: Kirill Reshke <[email-masked]>
Date: Thu, 15 Jan 2026 13:21:51 +0500

On Thu, 15 Jan 2026 at 12:46, Kirill Reshke <[email-masked]> wrote:
> 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

---

From: Kirill Reshke <[email-masked]>
Date: Thu, 15 Jan 2026 13:35:30 +0500

> [0] https://www.postgresql.org/message-id/lxzj26ga6ippdeunz6kuncectr5gfuugmm2ry22qu6hcx6oid6%40lzx3sjsqhmt6

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

---

From: Kirill Reshke <[email-masked]>
Date: Thu, 15 Jan 2026 22:59:31 +0500

>   disable_seq disable_bitmap

PFA v2 which leaves the test in-place.

Also commit message improvements.

-- 
Best regards,
Kirill Reshke