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Re: ALTER TABLE SET ACCESS METHOD on partitioned tables

Michael Paquier <michael@paquier.xyz>

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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
Date: 2023-06-01T12:50:50Z
Lists: pgsql-hackers 
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

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Add information about access method for partitioned relations in \dP+

  2. Fix dumps of partitioned tables with table AMs

  3. Don't use the pg_am system catalog in new test

  4. ALTER TABLE: rework determination of access method ID

  5. Allow specifying an access method for partitioned tables

  6. Review wording on tablespaces w.r.t. partitioned tables

  7. Add support for DEFAULT in ALTER TABLE .. SET ACCESS METHOD

  8. Update comment of AlterTableCmd->name in parsenodes.h