Feedback-ID: i0fe9450f:Fastmail
Date: Thu, 1 Jun 2023 08:50:50 -0400
From: Michael Paquier <michael@paquier.xyz>
To: Justin Pryzby <pryzby@telsasoft.com>
Cc: Soumyadeep Chakraborty <soumyadeep2007@gmail.com>,
	Zhihong Yu <zyu@yugabyte.com>, pgsql-hackers@postgresql.org,
	Ashwin Agrawal <ashwinstar@gmail.com>, vanjared@vmware.com
Subject: Re: ALTER TABLE SET ACCESS METHOD on partitioned tables
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On Wed, May 31, 2023 at 06:35:34PM -0500, Justin Pryzby wrote:
> What do you think the comment ought to say ?  It already says:
>
> src/backend/catalog/heap.c-              * Make a dependency link to force the relation to be deleted if its
> src/backend/catalog/heap.c-              * access method is.

This is the third location where we rely on the fact that
RELKIND_HAS_TABLE_AM() does not include RELKIND_PARTITIONED_TABLE, so
it seems worth documenting what we are relying on as a comment?  Say:
 * Make a dependency link to force the relation to be deleted if its
 * access method is.
 *
 * No need to add an explicit dependency for the toast table, as the
 * main table depends on it.  Partitioned tables have a table access
 * method defined, and RELKIND_HAS_TABLE_AM ignores them.

>> Speaking of which, ATExecSetAccessMethodNoStorage() does a catalog
>> update even if ALTER TABLE is defined to use the same table AM as what
>> is currently set.  There is no need to update the relation's pg_class
>> entry in this case.  Be careful that InvokeObjectPostAlterHook() still
>> needs to be checked in this case.  Perhaps some tests should be added
>> in test_oat_hooks.sql?  It would be tempted to add a new SQL file for
>> that.
>
> Are you suggesting to put this in a conditional: if oldrelam!=newAccessMethod ?

Yes, that's what I would add with a few lines close to the beginning
of ATExecSetTableSpaceNoStorage() to save from catalog updates if
these are not needed.
--
Michael

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