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Subject: Re: docs: clarify ALTER TABLE behavior on partitioned tables
From: Chao Li <li.evan.chao@gmail.com>
In-Reply-To: <CAEoWx2=mYhCfsnHaN96Qqwq5b0GVS2YgO3zpVqPPRd_iO52wRw@mail.gmail.com>
Date: Wed, 7 Jan 2026 16:27:45 +0800
Cc: Amit Kapila <amit.kapila16@gmail.com>
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Message-Id: <90F9169D-135C-45E5-8221-4F79DAED98E2@gmail.com>
References: <CAEoWx2=mYhCfsnHaN96Qqwq5b0GVS2YgO3zpVqPPRd_iO52wRw@mail.gmail.com>
To: Postgres hackers <pgsql-hackers@lists.postgresql.org>
Archived-At: <https://www.postgresql.org/message-id/90F9169D-135C-45E5-8221-4F79DAED98E2%40gmail.com>
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> On Jan 7, 2026, at 13:59, Chao Li <li.evan.chao@gmail.com> wrote:
>=20
> Hi Hackers,
>=20
> This task is derived from [1], as =E2=80=9CALTER TABLE=E2=80=9D is =
considered to exhibit =E2=80=9Cinconsistent=E2=80=9D behaviors with =
partitioned tables. =46rom the current documentation of =E2=80=9CALTER =
TABLE=E2=80=9D, readers won=E2=80=99t get enough information to form a =
clear understanding of how these commands behave with partitioned =
tables, and this gap needs to be addressed.
>=20
> I have spent several days verifying sub-commands of =E2=80=9CALTER =
TABLE=E2=80=9D one by one against partitioned tables from the following =
points:
>=20
> 1) Does an action on a parent partitioned table propagate to child =
partitions?
> 2) Does a value set on a parent partitioned table get automatically =
inherited by newly created partitions?
> 3) Does =E2=80=9CONLY partitioned-table=E2=80=9D work as the =
documentation states (preventing propagation)?
> 4) Can an action be performed on a partitioned table and its children =
independently?
>=20
> =46rom these four criteria, sub-commands fall into the following =
categories:
>=20
> C1 - Sub-commands that can only be used with a partitioned table; ONLY =
will lead to an error; using them with a child partition will lead to an =
error.
>=20
>  * ADD COLUMN
>  * DROP COLUMN
>  * SET DATA TYPE
>  * DROP EXPRESSION
>  * ADD GENERATED AS IDENTITY
>  * ADD GENERATED
>  * DROP IDENTITY
>  * SET sequence_option
>  * RESTART
>  * ALTER CONSTRAINT
>=20
>=20
> C2 - Sub-commands where using them with a partitioned table will =
automatically propagate to child partitions; ONLY prevents propagation; =
new partitions
> inherit the parent=E2=80=99s new setting; and child partitions can be =
set to different values than the parent.
>=20
>  * SET DEFAULT
>  * DROP DEFAULT
>  * SET EXPRESSION AS
>  * SET STORAGE
>  * DROP CONSTRAINT
>  * ENABLE/DISABLE [ REPLICA | ALWAYS] TRIGGER
>=20
> C3 - Slightly different from C2: new partitions will not inherit the =
parent=E2=80=99s setting.
>=20
>  * SET STATISTICS
>=20
> C4 - Sub-commands that can be used on a partitioned table and child =
partitions independently; actions on the parent will not propagate to =
children; children
> can have different settings than the parent; new partitions will not =
inherit the parent=E2=80=99s setting; ONLY can be used but has no =
effect.
>=20
>  * SET/RESET (attribute_option =3D value)
>  * ENABLE/DISABLE [ REPLICA | ALWAYS] RULE
>  * ENABLE/DISABLE ROW LEVEL SECURITY
>  * NO FORCE / FORCE ROW LEVEL SECURITY
>  * OWNER TO
>  * REPLICA IDENTITY
>  * SET SCHEMA
>=20
> C5 - Slightly different from C4: new partitions will automatically =
inherit the parent=E2=80=99s setting.
>=20
>  * SET COMPRESSION
>=20
> C6 - Slightly different from C2: ONLY cannot be used with a parent =
partitioned table, meaning the setting must be propagated to child =
partitions.
>=20
>  * ADD table_constraint
>=20
> C7 - Sub-commands that cannot be used with a partitioned table, but =
can only be used with a leaf partition.
>=20
>  * ADD table_constraint_with_index
>  * ALTER CONSTRAINT =E2=80=A6 INHERIT / NO INHERIT
>  * CLUSTER ON
>  * SET WITHOUT CLUSTER
>  * SET { LOGGED | UNLOGGED }
>  * SET (storage_parameter)
>=20
>=20
> C8 - Slightly different from C1: child partitions can set different =
values than the parent.
>=20
>  * VALIDATE CONSTRAINT
>=20
> C9 - Slightly different from C2: if the parent has a value, then new =
partitions will inherit that value; otherwise, they use the default from =
the GUC.
>=20
>  * SET ACCESS METHOD
>=20
> C10 - Sub-commands used with a parent partitioned table will NOT =
propagate to child partitions; but new partitions will automatically =
inherit the parent=E2=80=99s setting; partitions can be set to different =
values than the parent; ONLY can be used but has no effect.
>=20
> * SET TABLESPACE
>=20
> C11 - Sub-commands used with a parent partitioned table won=E2=80=99t =
fail but do nothing; using them with a leaf partition works as with a =
normal table.
>=20
>  * RESET (storage_parameter)  # this appears questionable, because SET =
(storage_parameter) is not allowed on a partitioned table
>=20
> C12 - Sub-commands that don=E2=80=99t support partitioned tables; =
neither parent partitioned tables nor child partitions.
>=20
>  * INHERIT parent_table
>  * NO INHERIT parent_table
>=20
> C13 - Sub-commands that support only parent partitioned tables; ONLY =
can be used but has no effect; using them with a child partition will =
fail.
>   * OF type
>  * NOT OF
>=20
> C14 - Sub-commands that treat partitioned tables, either parent =
partitioned tables or child partitions, as normal tables, so no =
propagation occurs; ONLY can be used but has no effect.
>=20
>  * RENAME
>=20
> C15 - Sub-commands that operate on partitioned tables.
>=20
>  * ATTACH PARTITION
>  * DETACH PARTITION
>  * MERGE PARTITIONS
>  * SPLIT PARTITION
>=20
> =E2=80=94 End of categories =E2=80=94
>=20
> With these categories, we can clearly see where =E2=80=9Cinconsistencies=
=E2=80=9D exist, and measure whether future changes mitigate these =
=E2=80=9Cinconsistencies=E2=80=9D or make them worse. Some categories =
include only one or two sub-commands; maybe they can be adjusted to =
other categories so that some categories are eliminated and the overall =
=E2=80=9Cinconsistency=E2=80=9D situation is improved.
>=20
> In this patch, I just want to add clarifications to the =E2=80=9CALTER =
TABLE=E2=80=9D documentation, without changing any existing behaviors.
>=20
> This patch is pretty massive. Although I have done a self-review, I =
may still have missed things. I know this patch is a challenge for =
reviewers, so I=E2=80=99m open to any suggestions to make it easier to =
review and commit, such as splitting it in some way.
>=20
>=20
> [1] =
https://postgr.es/m/CAEoWx2nJ71hy8R614HQr7vQhkBReO9AANPODPg0aSQs74eOdLQ@ma=
il.gmail.com
>=20
> --
> Chao Li (Evan)
> HighGo Software Co., Ltd.
> https://www.highgo.com/
>=20
>=20
>=20
>=20
> <v1-0001-docs-clarify-ALTER-TABLE-behavior-on-partitioned-.patch>

Added to CF: https://commitfest.postgresql.org/patch/6379/

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