Fix detach of a partition that has a toplevel FK to a partitioned table

alvherre · alvherre · commit 9b21f203dd87 · 2025-01-21T14:53:46.000+01:00
In common cases, foreign keys are defined on the toplevel partitioned table; but if instead one is defined on a partition and references a partitioned table, and the referencing partition is detached, we would examine the pg_constraint row on the partition being detached, and fail to realize that the sub-constraints must be left alone. This causes the ALTER TABLE DETACH process to fail with ERROR: could not find ON INSERT check triggers of foreign key constraint NNN This is similar but not quite the same as what was fixed by 53af949. This bug doesn't affect branches earlier than 15, because the detach procedure was different there, so we only backpatch down to 15. Fix by skipping such modifying constraints that are children of other constraints being detached. Author: Amul Sul <sulamul@gmail.com> Diagnosys-by: Sami Imseih <samimseih@gmail.com> Discussion: https://postgr.es/m/CAAJ_b97GuPh6wQPbxQS-Zpy16Oh+0aMv-w64QcGrLhCOZZ6p+g@mail.gmail.com
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
@@ -19987,6 +19987,7 @@ DetachPartitionFinalize(Relation rel, Relation partRel, bool concurrent,
 	HeapTuple	tuple,
 				newtuple;
 	Relation	trigrel = NULL;
+	List	   *fkoids = NIL;
 
 	if (concurrent)
 	{
@@ -20007,6 +20008,23 @@ DetachPartitionFinalize(Relation rel, Relation partRel, bool concurrent,
 	fks = copyObject(RelationGetFKeyList(partRel));
 	if (fks != NIL)
 		trigrel = table_open(TriggerRelationId, RowExclusiveLock);
+
+	/*
+	 * It's possible that the partition being detached has a foreign key that
+	 * references a partitioned table.  When that happens, there are multiple
+	 * pg_constraint rows for the partition: one points to the partitioned
+	 * table itself, while the others point to each of its partitions.  Only
+	 * the topmost one is to be considered here; the child constraints must be
+	 * left alone, because conceptually those aren't coming from our parent
+	 * partitioned table, but from this partition itself.
+	 *
+	 * We implement this by collecting all the constraint OIDs in a first scan
+	 * of the FK array, and skipping in the loop below those constraints whose
+	 * parents are listed here.
+	 */
+	foreach_node(ForeignKeyCacheInfo, fk, fks)
+		fkoids = lappend_oid(fkoids, fk->conoid);
+
 	foreach(cell, fks)
 	{
 		ForeignKeyCacheInfo *fk = lfirst(cell);
@@ -20020,9 +20038,13 @@ DetachPartitionFinalize(Relation rel, Relation partRel, bool concurrent,
 			elog(ERROR, "cache lookup failed for constraint %u", fk->conoid);
 		conform = (Form_pg_constraint) GETSTRUCT(contup);
 
-		/* consider only the inherited foreign keys */
+		/*
+		 * Consider only inherited foreign keys, and only if their parents
+		 * aren't in the list.
+		 */
 		if (conform->contype != CONSTRAINT_FOREIGN ||
-			!OidIsValid(conform->conparentid))
+			!OidIsValid(conform->conparentid) ||
+			list_member_oid(fkoids, conform->conparentid))
 		{
 			ReleaseSysCache(contup);
 			continue;
diff --git a/src/test/regress/expected/foreign_key.out b/src/test/regress/expected/foreign_key.out
@@ -2351,6 +2351,13 @@ UPDATE pk SET a = 4002 WHERE a = 4000;
 DELETE FROM pk WHERE a = 4002;
 UPDATE pk SET a = 4502 WHERE a = 4500;
 DELETE FROM pk WHERE a = 4502;
+-- Also, detaching a partition that has the FK itself should work
+-- https://postgr.es/m/CAAJ_b97GuPh6wQPbxQS-Zpy16Oh+0aMv-w64QcGrLhCOZZ6p+g@mail.gmail.com
+CREATE TABLE ffk (a int, b int REFERENCES pk) PARTITION BY list (a);
+CREATE TABLE ffk1 PARTITION OF ffk FOR VALUES IN (1);
+ALTER TABLE ffk1 ADD FOREIGN KEY (a) REFERENCES pk;
+ALTER TABLE ffk DETACH PARTITION ffk1;
+DROP TABLE ffk, ffk1;
 CREATE SCHEMA fkpart4;
 SET search_path TO fkpart4;
 -- dropping/detaching PARTITIONs is prevented if that would break
diff --git a/src/test/regress/sql/foreign_key.sql b/src/test/regress/sql/foreign_key.sql
@@ -1672,6 +1672,14 @@ DELETE FROM pk WHERE a = 4002;
 UPDATE pk SET a = 4502 WHERE a = 4500;
 DELETE FROM pk WHERE a = 4502;
 
+-- Also, detaching a partition that has the FK itself should work
+-- https://postgr.es/m/CAAJ_b97GuPh6wQPbxQS-Zpy16Oh+0aMv-w64QcGrLhCOZZ6p+g@mail.gmail.com
+CREATE TABLE ffk (a int, b int REFERENCES pk) PARTITION BY list (a);
+CREATE TABLE ffk1 PARTITION OF ffk FOR VALUES IN (1);
+ALTER TABLE ffk1 ADD FOREIGN KEY (a) REFERENCES pk;
+ALTER TABLE ffk DETACH PARTITION ffk1;
+DROP TABLE ffk, ffk1;
+
 CREATE SCHEMA fkpart4;
 SET search_path TO fkpart4;
 -- dropping/detaching PARTITIONs is prevented if that would break
