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Subject: Re: Fix SPLIT PARTITION bound-overlap bug and other improvements
From: Chao Li <li.evan.chao@gmail.com>
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Date: Wed, 20 May 2026 07:36:32 +0800
Cc: Dmitry Koval <d.koval@postgrespro.ru>,
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To: Alexander Korotkov <aekorotkov@gmail.com>
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> On May 19, 2026, at 19:00, Alexander Korotkov <aekorotkov@gmail.com> =
wrote:
>=20
> Hi, Chao!
>=20
> 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:
>>>=20
>>> 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-Fix-SPLIT=
-PARTITION-hint-for-DEFAULT-partition-bo.patch><v3-0004-Reject-degenerate-=
SPLIT-PARTITION-with-DEFAULT-pa.patch>
>>>>=20
>>>> v3-0001 through v3-0003 look good to me.
>>>>=20
>>>> 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.
>>>=20
>>> Sure, take your time.
>>>=20
>>> ------
>>> Regards,
>>> Alexander Korotkov
>>> Supabase
>>=20
>> 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, =
locale=3D'und-u-ks-level2', deterministic =3D false);
>> CREATE COLLATION
>> evantest=3D# create table t (b text collate case_insensitive) =
partition 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.
>> ```
>>=20
>> 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 =
both 2, but the two bounds are actually different, because 'a' and 'A' =
are considered equal by the collation.
>>=20
>> 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 =
within the split partition=E2=80=99s bound, we need to check the reverse =
direction 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.
>>=20
>> 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.
>=20
> I've pushed 0001-0003. =20

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()). =20

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.
>=20

But I don=E2=80=99t see any change for regression test between v4 and =
v5. Maybe you forgot to save your changes?

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/