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From: Alexander Korotkov <aekorotkov@gmail.com>
Date: Wed, 20 May 2026 09:19:18 +0300
Message-ID: 
 <CAPpHfduDPA1vqhrSgLwmGY5+wVsrmK2AKsPQ2rZa_=QAn-y_XQ@mail.gmail.com>
Subject: Re: Fix SPLIT PARTITION bound-overlap bug and other improvements
To: Chao Li <li.evan.chao@gmail.com>
Cc: Dmitry Koval <d.koval@postgrespro.ru>,
	PostgreSQL-development <pgsql-hackers@postgresql.org>
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Hi, Chao!

On Wed, May 20, 2026 at 2:37=E2=80=AFAM Chao Li <li.evan.chao@gmail.com> wr=
ote:
> > On May 19, 2026, at 19:00, Alexander Korotkov <aekorotkov@gmail.com> wr=
ote:
> > On Tue, May 19, 2026 at 5:50=E2=80=AFAM Chao Li <li.evan.chao@gmail.com=
> wrote:
> >>> On May 18, 2026, at 20:04, Alexander Korotkov <aekorotkov@gmail.com> =
wrote:
> >>>
> >>> On Mon, May 18, 2026 at 2:57=E2=80=AFPM Chao Li <li.evan.chao@gmail.c=
om> wrote:
> >>>>> <v3-0003-Clarify-SPLIT-PARTITION-bound-requirements-in-doc.patch><v=
3-0001-Fix-SPLIT-PARTITION-range-bound-validation-with-D.patch><v3-0002-Fix=
-SPLIT-PARTITION-hint-for-DEFAULT-partition-bo.patch><v3-0004-Reject-degene=
rate-SPLIT-PARTITION-with-DEFAULT-pa.patch>
> >>>>
> >>>> v3-0001 through v3-0003 look good to me.
> >>>>
> >>>> For v3-0004, I have a suspicion, but it's late here and my brain is =
getting slow, so I would like to study it more tomorrow.
> >>>
> >>> Sure, take your time.
> >>>
> >>> ------
> >>> Regards,
> >>> Alexander Korotkov
> >>> Supabase
> >>
> >> My suspicion was that check_split_partition_not_same_bound() now has t=
wo paths. The RANGE path honors collation, while the LIST path does not. So=
 I spent some time creating a test that uses a case-insensitive collation:
> >> ```
> >> evantest=3D# create collation case_insensitive (provider=3Dicu, locale=
=3D'und-u-ks-level2', deterministic =3D false);
> >> CREATE COLLATION
> >> evantest=3D# create table t (b text collate case_insensitive) partitio=
n by list (b);
> >> CREATE TABLE
> >> evantest=3D# create table tp_ab partition of t for values in ('a', 'b'=
);
> >> CREATE TABLE
> >> evantest=3D# alter table t split partition tp_ab into
> >> evantest-#   (partition tp_a for values in ('a', 'A'),
> >> evantest(#   partition tp_default default);
> >> ERROR:  cannot split partition "tp_ab" only to add a DEFAULT partition
> >> LINE 2:   (partition tp_a for values in ('a', 'A'),
> >>                     ^
> >> DETAIL:  The non-DEFAULT partition would keep the same partition bound=
.
> >> HINT:  Use CREATE TABLE ... PARTITION OF ... DEFAULT to add a DEFAULT =
partition.
> >> ```
> >>
> >> In this test, the split partition=E2=80=99s bound is ('a', 'b'), and t=
he new partition=E2=80=99s bound is ('a', 'A'). Their list lengths are both=
 2, but the two bounds are actually different, because 'a' and 'A' are cons=
idered equal by the collation.
> >>
> >> So, in the LIST path, since check_partition_bounds_for_split_list() ha=
s already ensured that the new partition=E2=80=99s bound is contained withi=
n the split partition=E2=80=99s bound, we need to check the reverse directi=
on as well. Whether the split partition=E2=80=99s bound is also contained i=
n the new partition=E2=80=99s bound. If yes, the two bounds are identical.
> >>
> >> See the attached v4 for my changes for 0004. 0001-0003 are unchanged. =
Since 0001 and 0003 are independent of 0004, maybe they can be pushed first=
.
> >
> > I've pushed 0001-0003.
>
> Thanks for pushing them.
>
> > Thank you for discovering the collation issue
> > in 0004.  Note that original approach of using
> > partition_bounds_equal() can't handle different collations too (as it
> > internally uses datumIsEqual()).
>
> Yes, I realized that while reviewing v3. That=E2=80=99s reason I didn=E2=
=80=99t get back v2 and only worked again based on v3.
>
> > I've revised the remaining patch:
> > made function header comment a bit more detailed
>
> This part looks good to me.
>
> > and added additional
> > regression tests.  Please, check.
> >
>
> But I don=E2=80=99t see any change for regression test between v4 and v5.=
 Maybe you forgot to save your changes?

Sorry, I just mess up, no changes in tests.
I'm going to push this if no objection.

------
Regards,
Alexander Korotkov
Supabase