docs: clarify ALTER TABLE behavior on partitioned tables

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/