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From: Alexander Korotkov <aekorotkov@gmail.com>
Date: Wed, 20 May 2026 14:46:30 +0300
Message-ID: 
 <CAPpHfdvqk=nC-_wdK4o5=LyWD53FvJDdH7RSk7cZuWgx-qRCQg@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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On Wed, May 20, 2026 at 9:29=E2=80=AFAM Chao Li <li.evan.chao@gmail.com> wr=
ote:
> > On May 20, 2026, at 14:19, Alexander Korotkov <aekorotkov@gmail.com> wr=
ote:
> >
> > Hi, Chao!
> >
> > On Wed, May 20, 2026 at 2:37=E2=80=AFAM Chao Li <li.evan.chao@gmail.com=
> wrote:
> >>> On May 19, 2026, at 19:00, Alexander Korotkov <aekorotkov@gmail.com> =
wrote:
> >>> On Tue, May 19, 2026 at 5:50=E2=80=AFAM Chao Li <li.evan.chao@gmail.c=
om> 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=
.com> wrote:
> >>>>>>> <v3-0003-Clarify-SPLIT-PARTITION-bound-requirements-in-doc.patch>=
<v3-0001-Fix-SPLIT-PARTITION-range-bound-validation-with-D.patch><v3-0002-F=
ix-SPLIT-PARTITION-hint-for-DEFAULT-partition-bo.patch><v3-0004-Reject-dege=
nerate-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 i=
s 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=
 two 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, loca=
le=3D'und-u-ks-level2', deterministic =3D false);
> >>>> CREATE COLLATION
> >>>> evantest=3D# create table t (b text collate case_insensitive) partit=
ion 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 partiti=
on
> >>>> LINE 2:   (partition tp_a for values in ('a', 'A'),
> >>>>                    ^
> >>>> DETAIL:  The non-DEFAULT partition would keep the same partition bou=
nd.
> >>>> HINT:  Use CREATE TABLE ... PARTITION OF ... DEFAULT to add a DEFAUL=
T partition.
> >>>> ```
> >>>>
> >>>> In this test, the split partition=E2=80=99s bound is ('a', 'b'), and=
 the new partition=E2=80=99s bound is ('a', 'A'). Their list lengths are bo=
th 2, but the two bounds are actually different, because 'a' and 'A' are co=
nsidered equal by the collation.
> >>>>
> >>>> So, in the LIST path, since check_partition_bounds_for_split_list() =
has already ensured that the new partition=E2=80=99s bound is contained wit=
hin the split partition=E2=80=99s bound, we need to check the reverse direc=
tion as well. Whether the split partition=E2=80=99s bound is also contained=
 in 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 fir=
st.
> >>>
> >>> 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.
> >
>
> No worries. Then v5 looks good to me.

Thank you, pushed.

------
Regards,
Alexander Korotkov
Supabase