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help / color / mirror / Atom feedFrom: Kirill Reshke <[email protected]>
To: pgsql-hackers <[email protected]>
Subject: Re: Fix gistkillitems & add regression test to microvacuum
Date: Thu, 15 Jan 2026 22:59:31 +0500
Message-ID: <CALdSSPgfFWUBc8RoOZe5PmoUGa4LJUDeMTcAT8HwXGCMGJ9uBA@mail.gmail.com> (raw)
In-Reply-To: <CALdSSPh-QtT8NrhtKsNWwFVF3D4KX6Wy3qs-FPc16c6VAECEyg@mail.gmail.com>
References: <CALdSSPgZWX_D8+Fx4YQqRN5eW5iSx_rJdqQhCfdWTvqKXVfJ4w@mail.gmail.com>
<CALdSSPgPs=gKWkKN0=4yBd49FBY=ijxBz4YGV64vfVMK7YQhpw@mail.gmail.com>
<CALdSSPiaQptrccvRoHhP3=YqN9-K8duXfLHHm3G=+7FVL8A-Xw@mail.gmail.com>
<CALdSSPh-QtT8NrhtKsNWwFVF3D4KX6Wy3qs-FPc16c6VAECEyg@mail.gmail.com>
On Thu, 15 Jan 2026 at 13:35, Kirill Reshke <[email protected]> wrote:
>
> On Thu, 15 Jan 2026 at 13:21, Kirill Reshke <[email protected]> wrote:
> >
> > On Thu, 15 Jan 2026 at 12:46, Kirill Reshke <[email protected]> wrote:
> > >
> > > On Thu, 15 Jan 2026 at 12:00, Kirill Reshke <[email protected]> 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%40lzx3sjsqh...
> >
> >
> > --
> > 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
Attachments:
[application/octet-stream] v2-0001-Fix-gistkillitems-for-GiST-ROOT-page.patch (3.0K, 2-v2-0001-Fix-gistkillitems-for-GiST-ROOT-page.patch)
download | inline diff:
From c6d89d6bdcda3bd53beb120be77f24838e4b5b3d Mon Sep 17 00:00:00 2001
From: reshke <[email protected]>
Date: Thu, 15 Jan 2026 06:34:42 +0000
Subject: [PATCH v2] Fix gistkillitems for GiST ROOT page.
GiST index killitems feature misbehaves for single-page
(ROOT-only) GiST index. This is caused by GiST scan
"current block" variable not beign initialized for
very first-to-scan page (which is ROOT page).
Fix this by moving variable initialization in
read pgae utility function. Also adjust test output
that used to test exactly this bug (starting 377b7ab).
Discussion: https://postgr.es/m/CALdSSPgZWX_D8%2BFx4YQqRN5eW5iSx_rJdqQhCfdWTvqKXVfJ4w%40mail.gmail.com
Discussion: https://postgr.es/m/lxzj26ga6ippdeunz6kuncectr5gfuugmm2ry22qu6hcx6oid6@lzx3sjsqhmt6
---
src/backend/access/gist/gistget.c | 6 +++---
src/test/modules/index/expected/killtuples.out | 2 +-
src/test/modules/index/specs/killtuples.spec | 2 +-
3 files changed, 5 insertions(+), 5 deletions(-)
diff --git a/src/backend/access/gist/gistget.c b/src/backend/access/gist/gistget.c
index 11b214eb99b..7dc34680e2d 100644
--- a/src/backend/access/gist/gistget.c
+++ b/src/backend/access/gist/gistget.c
@@ -407,6 +407,9 @@ gistScanPage(IndexScanDesc scan, GISTSearchItem *pageItem,
*/
so->curPageLSN = BufferGetLSNAtomic(buffer);
+ /* save current item BlockNumber for gistkillitems() call */
+ so->curBlkno = pageItem->blkno;
+
/*
* check all tuples on page
*/
@@ -722,9 +725,6 @@ gistgettuple(IndexScanDesc scan, ScanDirection dir)
CHECK_FOR_INTERRUPTS();
- /* save current item BlockNumber for next gistkillitems() call */
- so->curBlkno = item->blkno;
-
/*
* While scanning a leaf page, ItemPointers of matching heap
* tuples are stored in so->pageData. If there are any on
diff --git a/src/test/modules/index/expected/killtuples.out b/src/test/modules/index/expected/killtuples.out
index be7ddd756ef..f504eca76df 100644
--- a/src/test/modules/index/expected/killtuples.out
+++ b/src/test/modules/index/expected/killtuples.out
@@ -223,7 +223,7 @@ step flush: SELECT FROM pg_stat_force_next_flush();
step result: SELECT heap_blks_read + heap_blks_hit - counter.heap_accesses AS new_heap_accesses FROM counter, pg_statio_all_tables WHERE relname = 'kill_prior_tuple';
new_heap_accesses
-----------------
- 1
+ 0
(1 row)
step drop_table: DROP TABLE IF EXISTS kill_prior_tuple;
diff --git a/src/test/modules/index/specs/killtuples.spec b/src/test/modules/index/specs/killtuples.spec
index 77fe8c689a7..7f912a40f1f 100644
--- a/src/test/modules/index/specs/killtuples.spec
+++ b/src/test/modules/index/specs/killtuples.spec
@@ -94,7 +94,7 @@ permutation
measure access flush result
drop_table drop_ext_btree_gist
-# Test gist, but with fewer rows - shows that killitems doesn't work anymore!
+# Test gist, but with fewer rows - that killitems used to be buggy.
permutation
create_table fill_10 create_ext_btree_gist create_gist flush
disable_seq disable_bitmap
--
2.43.0
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Subject: Re: Fix gistkillitems & add regression test to microvacuum
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