Re: docs: clarify ALTER TABLE behavior on partitioned tables

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From: Chao Li <[email protected]>
To: Postgres hackers <[email protected]>
Cc: Amit Kapila <[email protected]>
Subject: Re: docs: clarify ALTER TABLE behavior on partitioned tables
Date: Wed, 7 Jan 2026 16:27:45 +0800
Message-ID: <[email protected]> (raw)
In-Reply-To: <CAEoWx2=mYhCfsnHaN96Qqwq5b0GVS2YgO3zpVqPPRd_iO52wRw@mail.gmail.com>
References: <CAEoWx2=mYhCfsnHaN96Qqwq5b0GVS2YgO3zpVqPPRd_iO52wRw@mail.gmail.com>



> On Jan 7, 2026, at 13:59, Chao Li <[email protected]> wrote:
> 
> Hi Hackers,
> 
> This task is derived from [1], as “ALTER TABLE” is considered to exhibit “inconsistent” behaviors with partitioned tables. From the current documentation of “ALTER TABLE”, readers won’t get enough information to form a clear understanding of how these commands behave with partitioned tables, and this gap needs to be addressed.
> 
> I have spent several days verifying sub-commands of “ALTER TABLE” one by one against partitioned tables from the following points:
> 
> 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 “ONLY partitioned-table” work as the documentation states (preventing propagation)?
> 4) Can an action be performed on a partitioned table and its children independently?
> 
> From these four criteria, sub-commands fall into the following categories:
> 
> 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.
> 
>  * ADD COLUMN
>  * DROP COLUMN
>  * SET DATA TYPE
>  * DROP EXPRESSION
>  * ADD GENERATED AS IDENTITY
>  * ADD GENERATED
>  * DROP IDENTITY
>  * SET sequence_option
>  * RESTART
>  * ALTER CONSTRAINT
> 
> 
> C2 - Sub-commands where using them with a partitioned table will automatically propagate to child partitions; ONLY prevents propagation; new partitions
> inherit the parent’s new setting; and child partitions can be set to different values than the parent.
> 
>  * SET DEFAULT
>  * DROP DEFAULT
>  * SET EXPRESSION AS
>  * SET STORAGE
>  * DROP CONSTRAINT
>  * ENABLE/DISABLE [ REPLICA | ALWAYS] TRIGGER
> 
> C3 - Slightly different from C2: new partitions will not inherit the parent’s setting.
> 
>  * SET STATISTICS
> 
> 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’s setting; ONLY can be used but has no effect.
> 
>  * SET/RESET (attribute_option = value)
>  * ENABLE/DISABLE [ REPLICA | ALWAYS] RULE
>  * ENABLE/DISABLE ROW LEVEL SECURITY
>  * NO FORCE / FORCE ROW LEVEL SECURITY
>  * OWNER TO
>  * REPLICA IDENTITY
>  * SET SCHEMA
> 
> C5 - Slightly different from C4: new partitions will automatically inherit the parent’s setting.
> 
>  * SET COMPRESSION
> 
> C6 - Slightly different from C2: ONLY cannot be used with a parent partitioned table, meaning the setting must be propagated to child partitions.
> 
>  * ADD table_constraint
> 
> C7 - Sub-commands that cannot be used with a partitioned table, but can only be used with a leaf partition.
> 
>  * ADD table_constraint_with_index
>  * ALTER CONSTRAINT … INHERIT / NO INHERIT
>  * CLUSTER ON
>  * SET WITHOUT CLUSTER
>  * SET { LOGGED | UNLOGGED }
>  * SET (storage_parameter)
> 
> 
> C8 - Slightly different from C1: child partitions can set different values than the parent.
> 
>  * VALIDATE CONSTRAINT
> 
> 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.
> 
>  * SET ACCESS METHOD
> 
> C10 - Sub-commands used with a parent partitioned table will NOT propagate to child partitions; but new partitions will automatically inherit the parent’s setting; partitions can be set to different values than the parent; ONLY can be used but has no effect.
> 
> * SET TABLESPACE
> 
> C11 - Sub-commands used with a parent partitioned table won’t fail but do nothing; using them with a leaf partition works as with a normal table.
> 
>  * RESET (storage_parameter)  # this appears questionable, because SET (storage_parameter) is not allowed on a partitioned table
> 
> C12 - Sub-commands that don’t support partitioned tables; neither parent partitioned tables nor child partitions.
> 
>  * INHERIT parent_table
>  * NO INHERIT parent_table
> 
> 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
> 
> 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.
> 
>  * RENAME
> 
> C15 - Sub-commands that operate on partitioned tables.
> 
>  * ATTACH PARTITION
>  * DETACH PARTITION
>  * MERGE PARTITIONS
>  * SPLIT PARTITION
> 
> — End of categories —
> 
> With these categories, we can clearly see where “inconsistencies” exist, and measure whether future changes mitigate these “inconsistencies” 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 “inconsistency” situation is improved.
> 
> In this patch, I just want to add clarifications to the “ALTER TABLE” documentation, without changing any existing behaviors.
> 
> 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’m open to any suggestions to make it easier to review and commit, such as splitting it in some way.
> 
> 
> [1] https://postgr.es/m/CAEoWx2nJ71hy8R614HQr7vQhkBReO9AANPODPg0aSQs74eOdLQ@mail.gmail.com
> 
> --
> Chao Li (Evan)
> HighGo Software Co., Ltd.
> https://www.highgo.com/
> 
> 
> 
> 
> <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/

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