Feedback-ID: ia2694551:Fastmail
Date: Mon, 24 Mar 2025 16:47:31 +0100
From: =?utf-8?Q?=C3=81lvaro?= Herrera <alvherre@alvh.no-ip.org>
To: Shlok Kyal <shlok.kyal.oss@gmail.com>
Cc: vignesh C <vignesh21@gmail.com>,
	Sergey Tatarintsev <s.tatarintsev@postgrespro.ru>,
 pgsql-hackers@lists.postgresql.org
Subject: Re: Restrict publishing of partitioned table with a foreign table as
 partition
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One thing that bothers me a bit about this is that there's no single
code comment where this restriction it documented in full; in fact it
doesn't seem documented anywhere, only in the commit message.

I think check_foreign_tables() is a good place to add an explanatory
comment; other places can reference that.  For instance, add something
like

/*
 * Protect against including foreign tables that are partitions of
 * partitioned tables published by the given publication.  This would
 * not work properly, because <!-- explain reason -->, so we disallow
 * the case here and in all DDL commands that would end up creating
 * such a case indirectly.
 */

Then for instance in check_publication_add_relation() and
ATExecAttachPartition() you comment would say /* if the would-be
partition is a foreign table, verify that the partitioned table is not
in a publication with publish_via_root=false.  See check_foreign_tables
for details */


Also, surely we should document this restriction in the SGML docs
somewhere.


Would it be better if check_partrel_has_foreign_table() used
RelationGetPartitionDesc(omit_detached=true) instead of
find_all_inheritors()?

I'm wary of all those accesses of subscription/publication catalogs in
DDL code.  Maybe I worry about nothing, but I cannot but feel that we're
missing one layer of abstraction there (including possibly some caching
on top of syscache).

I think this
castNode(RangeVar, lfirst(list_head(stmt->base.inhRelations)));
is better written
linitial_node(RangeVar, stmt->base.inhRelations);

-- 
Álvaro Herrera         PostgreSQL Developer  —  https://www.EnterpriseDB.com/
"Tiene valor aquel que admite que es un cobarde" (Fernandel)