Fix self-referencing foreign keys with partitioned tables

There are a number of bugs in this area.  Two of them are fixed here,
namely:
1. get_relation_idx_constraint_oid does not restrict the type of
   constraint that's returned, so with sufficient bad luck it can
   return the OID of a foreign key constraint.  This has the effect that
   a primary key in a partition can end up as a child of a foreign key,
   which makes no sense (it needs to be the child of the equivalent
   primary key.)
   Change the API contract so that only index-backed constraints are
   returned, mimicking get_constraint_index().

2. Both CloneFkReferenced and CloneFkReferencing clone a
   self-referencing foreign key, so the partition ends up with
   a duplicate foreign key.  Change the former function to ignore such
   constraints.

Add some tests to verify that things are better now.  (However, these
new tests show some additional misbehavior that will be fixed later --
namely that there's a constraint marked NOT VALID.)

Backpatch to 12, where these constraints are possible at all.

Author: Jehan-Guillaume de Rorthais <jgdr@dalibo.com>
Discussion: https://postgr.es/m/20220603154232.1715b14c@karst

1 files changed, 13 insertions, 0 deletions

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 3df5c5681f3..4d67176b64b 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -9356,6 +9356,8 @@ CloneForeignKeyConstraints(List **wqueue, Relation parentRel,
  * clone those constraints to the given partition.  This is to be called
  * when the partition is being created or attached.
  *
+ * This ignores self-referencing FKs; those are handled by CloneFkReferencing.
+ *
  * This recurses to partitions, if the relation being attached is partitioned.
  * Recursion is done by calling addFkRecurseReferenced.
  */
@@ -9432,6 +9434,17 @@ CloneFkReferenced(Relation parentRel, Relation partitionRel)
 		}
 
 		/*
+		 * Don't clone self-referencing foreign keys, which can be in the
+		 * partitioned table or in the partition-to-be.
+		 */
+		if (constrForm->conrelid == RelationGetRelid(parentRel) ||
+			constrForm->conrelid == RelationGetRelid(partitionRel))
+		{
+			ReleaseSysCache(tuple);
+			continue;
+		}
+
+		/*
 		 * Because we're only expanding the key space at the referenced side,
 		 * we don't need to prevent any operation in the referencing table, so
 		 * AccessShareLock suffices (assumes that dropping the constraint