Feedback-ID: ia2694551:Fastmail
Date: Tue, 23 Aug 2022 18:30:06 +0200
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Jehan-Guillaume de Rorthais <jgdr@dalibo.com>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: [BUG] parenting a PK constraint to a self-FK one  (Was: Self FK
 oddity when attaching a partition)
Message-ID: <20220823163006.smdpovyl4dhcakvr@alvherre.pgsql>
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On 2022-Aug-23, Jehan-Guillaume de Rorthais wrote:

Hi,

[...]

> However, it seems get_relation_idx_constraint_oid(), introduced in eb7ed3f3063,
> assume there could be only ONE constraint depending to an index. But in fact,
> multiple constraints can rely on the same index, eg.: the PK and a self
> referencing FK. In consequence, when looking for a constraint depending on an
> index for the given relation, either the FK or a PK can appears first depending
> on various conditions. It is then possible to trick it make a FK constraint a
> parent of a PK...

Hmm, wow, that sounds extremely stupid.  I think a sufficient fix might
be to have get_relation_idx_constraint_oid ignore any constraints that
are not unique or primary keys.  I tried your scenario with the attached
and it seems to work correctly.  Can you confirm?  (I only ran the
pg_regress tests, not anything else for now.)

If this is OK, we should make this API quirkiness very explicit in the
comments, so the patch needs to be a few lines larger in order to be
committable.  Also, perhaps the check should be that contype equals
either primary or unique, rather than it doesn't equal foreign.

-- 
Álvaro Herrera               48°01'N 7°57'E  —  https://www.EnterpriseDB.com/

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From a39299db23f4b2495b3ba10e7adb1121f0271694 Mon Sep 17 00:00:00 2001
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
Date: Tue, 23 Aug 2022 18:17:24 +0200
Subject: [PATCH] test fix

---
 src/backend/catalog/pg_constraint.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/backend/catalog/pg_constraint.c b/src/backend/catalog/pg_constraint.c
index bb65fb1e0a..71b6fb35e6 100644
--- a/src/backend/catalog/pg_constraint.c
+++ b/src/backend/catalog/pg_constraint.c
@@ -1011,6 +1011,14 @@ get_relation_idx_constraint_oid(Oid relationId, Oid indexId)
 		Form_pg_constraint constrForm;
 
 		constrForm = (Form_pg_constraint) GETSTRUCT(tuple);
+
+		/*
+		 * Foreign key constraints are ignored for these purposes,
+		 * because ...?
+		 */
+		if (constrForm->contype == CONSTRAINT_FOREIGN)
+			continue;
+
 		if (constrForm->conindid == indexId)
 		{
 			constraintId = constrForm->oid;
-- 
2.30.2


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