Allow NOT VALID foreign key constraints on partitioned tables.

When merging an existing foreign key during the addition or attachment
of a partition, consider the following:

1. If the parent foreign key constraint being added is NOT VALID, the
   validity flag of the matching child constraint is ignored. It is
   harmless for the child constraint to remain valid.

2. If the parent foreign key constraint being added is VALID and the
   matching child constraint is NOT VALID, the we implicitly validates
   the child constraint, marking it as valid. This behavior is
   consistent with creating a new constraint on the child table rather
   than attaching it to an existing one, as it ensures the child data
   is validated.

Author: EDB-AmulSul

doc/src/sgml/ref/alter_table.sgml

@@ -486,8 +486,6 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
      <para>
       Additional restrictions apply when unique or primary key constraints
       are added to partitioned tables; see <link linkend="sql-createtable"><command>CREATE TABLE</command></link>.
-      Also, foreign key constraints on partitioned
-      tables may not be declared <literal>NOT VALID</literal> at present.
      </para>
 
     </listitem>

src/backend/commands/tablecmds.c

@@ -574,8 +574,9 @@ static void createForeignKeyActionTriggers(Relation rel, Oid refRelOid,
 										   Oid indexOid,
 										   Oid parentDelTrigger, Oid parentUpdTrigger,
 										   Oid *deleteTrigOid, Oid *updateTrigOid);
-static bool tryAttachPartitionForeignKey(ForeignKeyCacheInfo *fk,
-										 Oid partRelid,
+static bool tryAttachPartitionForeignKey(List **wqueue,
+										 ForeignKeyCacheInfo *fk,
+										 Relation partition,
 										 Oid parentConstrOid, int numfks,
 										 AttrNumber *mapped_conkey, AttrNumber *confkey,
 										 Oid *conpfeqop,
@@ -9772,22 +9773,12 @@ ATAddForeignKeyConstraint(List **wqueue, AlteredTableInfo *tab, Relation rel,
 	 * Validity checks (permission checks wait till we have the column
 	 * numbers)
 	 */
-	if (rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
-	{
-		if (!recurse)
-			ereport(ERROR,
-					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
-					 errmsg("cannot use ONLY for foreign key on partitioned table \"%s\" referencing relation \"%s\"",
-							RelationGetRelationName(rel),
-							RelationGetRelationName(pkrel))));
-		if (fkconstraint->skip_validation && !fkconstraint->initially_valid)
-			ereport(ERROR,
-					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
-					 errmsg("cannot add NOT VALID foreign key on partitioned table \"%s\" referencing relation \"%s\"",
-							RelationGetRelationName(rel),
-							RelationGetRelationName(pkrel)),
-					 errdetail("This feature is not yet supported on partitioned tables.")));
-	}
+	if (!recurse && rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
+		ereport(ERROR,
+				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+				 errmsg("cannot use ONLY for foreign key on partitioned table \"%s\" referencing relation \"%s\"",
+						RelationGetRelationName(rel),
+						RelationGetRelationName(pkrel))));
 
 	if (pkrel->rd_rel->relkind != RELKIND_RELATION &&
 		pkrel->rd_rel->relkind != RELKIND_PARTITIONED_TABLE)
@@ -10782,8 +10773,7 @@ addFkRecurseReferencing(List **wqueue, Constraint *fkconstraint, Relation rel,
 		 */
 		for (int i = 0; i < pd->nparts; i++)
 		{
-			Oid			partitionId = pd->oids[i];
-			Relation	partition = table_open(partitionId, lockmode);
+			Relation	partition = table_open(pd->oids[i], lockmode);
 			List	   *partFKs;
 			AttrMap    *attmap;
 			AttrNumber	mapped_fkattnum[INDEX_MAX_KEYS];
@@ -10807,8 +10797,9 @@ addFkRecurseReferencing(List **wqueue, Constraint *fkconstraint, Relation rel,
 				ForeignKeyCacheInfo *fk;
 
 				fk = lfirst_node(ForeignKeyCacheInfo, cell);
-				if (tryAttachPartitionForeignKey(fk,
-												 partitionId,
+				if (tryAttachPartitionForeignKey(wqueue,
+												 fk,
+												 partition,
 												 parentConstr,
 												 numfks,
 												 mapped_fkattnum,
@@ -11260,8 +11251,9 @@ CloneFkReferencing(List **wqueue, Relation parentRel, Relation partRel)
 		{
 			ForeignKeyCacheInfo *fk = lfirst_node(ForeignKeyCacheInfo, lc);
 
-			if (tryAttachPartitionForeignKey(fk,
-											 RelationGetRelid(partRel),
+			if (tryAttachPartitionForeignKey(wqueue,
+											 fk,
+											 partRel,
 											 parentConstrOid,
 											 numfks,
 											 mapped_conkey,
@@ -11364,8 +11356,9 @@ CloneFkReferencing(List **wqueue, Relation parentRel, Relation partRel)
  * return false.
  */
 static bool
-tryAttachPartitionForeignKey(ForeignKeyCacheInfo *fk,
-							 Oid partRelid,
+tryAttachPartitionForeignKey(List **wqueue,
+							 ForeignKeyCacheInfo *fk,
+							 Relation partition,
 							 Oid parentConstrOid,
 							 int numfks,
 							 AttrNumber *mapped_conkey,
@@ -11384,12 +11377,15 @@ tryAttachPartitionForeignKey(ForeignKeyCacheInfo *fk,
 	HeapTuple	trigtup;
 	Oid			insertTriggerOid,
 				updateTriggerOid;
+	bool		parentConstrIsValid;
+	bool		partConstrIsValid;
 
 	parentConstrTup = SearchSysCache1(CONSTROID,
 									  ObjectIdGetDatum(parentConstrOid));
 	if (!HeapTupleIsValid(parentConstrTup))
 		elog(ERROR, "cache lookup failed for constraint %u", parentConstrOid);
 	parentConstr = (Form_pg_constraint) GETSTRUCT(parentConstrTup);
+	parentConstrIsValid = parentConstr->convalidated;
 
 	/*
 	 * Do some quick & easy initial checks.  If any of these fail, we cannot
@@ -11412,17 +11408,18 @@ tryAttachPartitionForeignKey(ForeignKeyCacheInfo *fk,
 	}
 
 	/*
-	 * Looks good so far; do some more extensive checks.  Presumably the check
-	 * for 'convalidated' could be dropped, since we don't really care about
-	 * that, but let's be careful for now.
+	 * Looks good so far; perform more extensive checks except for
+	 * convalidated. There's no need to worry about it because attaching a
+	 * valid parent constraint to an invalid child constraint will eventually
+	 * trigger implicit data validation for the child.
 	 */
 	partcontup = SearchSysCache1(CONSTROID,
 								 ObjectIdGetDatum(fk->conoid));
 	if (!HeapTupleIsValid(partcontup))
 		elog(ERROR, "cache lookup failed for constraint %u", fk->conoid);
 	partConstr = (Form_pg_constraint) GETSTRUCT(partcontup);
+	partConstrIsValid = partConstr->convalidated;
 	if (OidIsValid(partConstr->conparentid) ||
-		!partConstr->convalidated ||
 		partConstr->condeferrable != parentConstr->condeferrable ||
 		partConstr->condeferred != parentConstr->condeferred ||
 		partConstr->confupdtype != parentConstr->confupdtype ||
@@ -11481,7 +11478,8 @@ tryAttachPartitionForeignKey(ForeignKeyCacheInfo *fk,
 
 	systable_endscan(scan);
 
-	ConstraintSetParentConstraint(fk->conoid, parentConstrOid, partRelid);
+	ConstraintSetParentConstraint(fk->conoid, parentConstrOid,
+								  RelationGetRelid(partition));
 
 	/*
 	 * Like the constraint, attach partition's "check" triggers to the
@@ -11492,10 +11490,10 @@ tryAttachPartitionForeignKey(ForeignKeyCacheInfo *fk,
 							   &insertTriggerOid, &updateTriggerOid);
 	Assert(OidIsValid(insertTriggerOid) && OidIsValid(parentInsTrigger));
 	TriggerSetParentTrigger(trigrel, insertTriggerOid, parentInsTrigger,
-							partRelid);
+							RelationGetRelid(partition));
 	Assert(OidIsValid(updateTriggerOid) && OidIsValid(parentUpdTrigger));
 	TriggerSetParentTrigger(trigrel, updateTriggerOid, parentUpdTrigger,
-							partRelid);
+							RelationGetRelid(partition));
 
 	/*
 	 * If the referenced table is partitioned, then the partition we're
@@ -11573,6 +11571,32 @@ tryAttachPartitionForeignKey(ForeignKeyCacheInfo *fk,
 	}
 
 	CommandCounterIncrement();
+
+	/*
+	 * If a valid parent constraint is attached to a NOT VALID child
+	 * constraint, implicitly trigger validation for the child constraint.
+	 * This behavior aligns with creating a new constraint on the child table
+	 * rather than attaching it to the existing one, as it would ultimately
+	 * validate the child data. Conversely, having an invalid parent
+	 * constraint while the child constraint is valid doesn't cause any harm.
+	 */
+	if (parentConstrIsValid && !partConstrIsValid)
+	{
+		Relation	conrel;
+
+		conrel = table_open(ConstraintRelationId, RowExclusiveLock);
+
+		partcontup = SearchSysCache1(CONSTROID, ObjectIdGetDatum(fk->conoid));
+		if (!HeapTupleIsValid(partcontup))
+			elog(ERROR, "cache lookup failed for constraint %u", fk->conoid);
+
+		/* Using the same lock as used in AT_ValidateConstraint */
+		QueueFKConstraintValidation(wqueue, conrel, partition, partcontup,
+									ShareUpdateExclusiveLock);
+		ReleaseSysCache(partcontup);
+		table_close(conrel, RowExclusiveLock);
+	}
+
 	return true;
 }
 
@@ -12113,7 +12137,7 @@ ATExecValidateConstraint(List **wqueue, Relation rel, char *constrName,
  *
  * Add an entry to the wqueue to validate the given foreign key constraint in
  * Phase 3 and update the convalidated field in the pg_constraint catalog
- * for the specified relation.
+ * for the specified relation and all its children.
  */
 static void
 QueueFKConstraintValidation(List **wqueue, Relation conrel, Relation rel,
@@ -12126,6 +12150,7 @@ QueueFKConstraintValidation(List **wqueue, Relation conrel, Relation rel,
 
 	con = (Form_pg_constraint) GETSTRUCT(contuple);
 	Assert(con->contype == CONSTRAINT_FOREIGN);
+	Assert(!con->convalidated);
 
 	if (rel->rd_rel->relkind == RELKIND_RELATION)
 	{
@@ -12151,9 +12176,48 @@ QueueFKConstraintValidation(List **wqueue, Relation conrel, Relation rel,
 	}
 
 	/*
-	 * We disallow creating invalid foreign keys to or from partitioned
-	 * tables, so ignoring the recursion bit is okay.
+	 * If the table at either end of the constraint is partitioned, we need to
+	 * recurse and handle every constraint that is a child of this constraint.
 	 */
+	if (rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE ||
+		get_rel_relkind(con->confrelid) == RELKIND_PARTITIONED_TABLE)
+	{
+		ScanKeyData pkey;
+		SysScanDesc pscan;
+		HeapTuple	childtup;
+
+		ScanKeyInit(&pkey,
+					Anum_pg_constraint_conparentid,
+					BTEqualStrategyNumber, F_OIDEQ,
+					ObjectIdGetDatum(con->oid));
+
+		pscan = systable_beginscan(conrel, ConstraintParentIndexId,
+								   true, NULL, 1, &pkey);
+
+		while (HeapTupleIsValid(childtup = systable_getnext(pscan)))
+		{
+			Form_pg_constraint childcon;
+			Relation	childrel;
+
+			childcon = (Form_pg_constraint) GETSTRUCT(childtup);
+
+			/*
+			 * If the child constraint has already been validated, no further
+			 * action is required for it or its descendants, as they are all
+			 * valid.
+			 */
+			if (childcon->convalidated)
+				continue;
+
+			childrel = table_open(childcon->conrelid, lockmode);
+
+			QueueFKConstraintValidation(wqueue, conrel, childrel, childtup,
+										lockmode);
+			table_close(childrel, NoLock);
+		}
+
+		systable_endscan(pscan);
+	}
 
 	/*
 	 * Now update the catalog, while we have the door open.

src/test/regress/expected/foreign_key.out

@@ -1571,6 +1571,97 @@ drop table pktable2, fktable2;
 --
 -- Foreign keys and partitioned tables
 --
+-- NOT VALID foreign key on partitioned table
+CREATE TABLE fk_notpartitioned_pk (a int, b int, PRIMARY KEY (a, b));
+CREATE TABLE fk_partitioned_fk (b int, a int) PARTITION BY RANGE (a, b);
+ALTER TABLE fk_partitioned_fk ADD FOREIGN KEY (a, b) REFERENCES fk_notpartitioned_pk NOT VALID;
+-- Attaching a child table with the same valid foreign key constraint.
+CREATE TABLE fk_partitioned_fk_1 (a int, b int);
+ALTER TABLE fk_partitioned_fk_1 ADD FOREIGN KEY (a, b) REFERENCES fk_notpartitioned_pk;
+ALTER TABLE fk_partitioned_fk ATTACH PARTITION fk_partitioned_fk_1 FOR VALUES FROM (0,0) TO (1000,1000);
+-- Child constraint will remain valid.
+SELECT conname, convalidated, conrelid::regclass FROM pg_constraint
+WHERE conrelid::regclass::text like 'fk_partitioned_fk%' ORDER BY oid;
+           conname            | convalidated |      conrelid       
+------------------------------+--------------+---------------------
+ fk_partitioned_fk_a_b_fkey   | f            | fk_partitioned_fk
+ fk_partitioned_fk_1_a_b_fkey | t            | fk_partitioned_fk_1
+(2 rows)
+
+-- Validate the constraint
+ALTER TABLE fk_partitioned_fk VALIDATE CONSTRAINT fk_partitioned_fk_a_b_fkey;
+-- All constraints are now valid.
+SELECT conname, convalidated, conrelid::regclass FROM pg_constraint
+WHERE conrelid::regclass::text like 'fk_partitioned_fk%' ORDER BY oid;
+           conname            | convalidated |      conrelid       
+------------------------------+--------------+---------------------
+ fk_partitioned_fk_a_b_fkey   | t            | fk_partitioned_fk
+ fk_partitioned_fk_1_a_b_fkey | t            | fk_partitioned_fk_1
+(2 rows)
+
+-- Attaching a child with a NOT VALID constraint.
+CREATE TABLE fk_partitioned_fk_2 (a int, b int);
+INSERT INTO fk_partitioned_fk_2 VALUES(1000, 1000); -- doesn't exist in referenced table
+ALTER TABLE fk_partitioned_fk_2 ADD FOREIGN KEY (a, b) REFERENCES fk_notpartitioned_pk NOT VALID;
+-- It will fail because the attach operation implicitly validates the data.
+ALTER TABLE fk_partitioned_fk ATTACH PARTITION fk_partitioned_fk_2 FOR VALUES FROM (1000,1000) TO (2000,2000);
+ERROR:  insert or update on table "fk_partitioned_fk_2" violates foreign key constraint "fk_partitioned_fk_2_a_b_fkey"
+DETAIL:  Key (a, b)=(1000, 1000) is not present in table "fk_notpartitioned_pk".
+-- Remove the invalid data and try again.
+TRUNCATE fk_partitioned_fk_2;
+ALTER TABLE fk_partitioned_fk ATTACH PARTITION fk_partitioned_fk_2 FOR VALUES FROM (1000,1000) TO (2000,2000);
+-- The child constraint will also be valid.
+SELECT conname, convalidated FROM pg_constraint WHERE conrelid = 'fk_partitioned_fk_2'::regclass;
+           conname            | convalidated 
+------------------------------+--------------
+ fk_partitioned_fk_2_a_b_fkey | t
+(1 row)
+
+-- Test case where the child constraint is invalid, the grandchild constraint
+-- is valid, and the validation for the grandchild should be skipped when a
+-- valid constraint is applied to the top parent.
+CREATE TABLE fk_partitioned_fk_3 (a int, b int) PARTITION BY RANGE (a, b);
+ALTER TABLE fk_partitioned_fk_3 ADD FOREIGN KEY (a, b) REFERENCES fk_notpartitioned_pk NOT VALID;
+CREATE TABLE fk_partitioned_fk_3_1 (a int, b int);
+ALTER TABLE fk_partitioned_fk_3_1 ADD FOREIGN KEY (a, b) REFERENCES fk_notpartitioned_pk;
+ALTER TABLE fk_partitioned_fk_3 ATTACH PARTITION fk_partitioned_fk_3_1 FOR VALUES FROM (2000,2000) TO (3000,3000);
+ALTER TABLE fk_partitioned_fk ATTACH PARTITION fk_partitioned_fk_3 FOR VALUES FROM (2000,2000) TO (3000,3000);
+-- All constraints are now valid.
+SELECT conname, convalidated, conrelid::regclass FROM pg_constraint
+WHERE conrelid::regclass::text like 'fk_partitioned_fk%' ORDER BY oid;
+            conname             | convalidated |       conrelid        
+--------------------------------+--------------+-----------------------
+ fk_partitioned_fk_a_b_fkey     | t            | fk_partitioned_fk
+ fk_partitioned_fk_1_a_b_fkey   | t            | fk_partitioned_fk_1
+ fk_partitioned_fk_2_a_b_fkey   | t            | fk_partitioned_fk_2
+ fk_partitioned_fk_3_a_b_fkey   | t            | fk_partitioned_fk_3
+ fk_partitioned_fk_3_1_a_b_fkey | t            | fk_partitioned_fk_3_1
+(5 rows)
+
+DROP TABLE fk_partitioned_fk, fk_notpartitioned_pk;
+-- NOT VALID foreign key on a non-partitioned table referencing a partitioned table
+CREATE TABLE fk_partitioned_pk (a int, b int, PRIMARY KEY (a, b)) PARTITION BY RANGE (a, b);
+CREATE TABLE fk_partitioned_pk_1 PARTITION OF fk_partitioned_pk FOR VALUES FROM (0,0) TO (1000,1000);
+CREATE TABLE fk_notpartitioned_fk (b int, a int);
+ALTER TABLE fk_notpartitioned_fk ADD FOREIGN KEY (a, b) REFERENCES fk_partitioned_pk NOT VALID;
+-- Constraint will be invalid.
+SELECT conname, convalidated FROM pg_constraint WHERE conrelid = 'fk_notpartitioned_fk'::regclass;
+            conname             | convalidated 
+--------------------------------+--------------
+ fk_notpartitioned_fk_a_b_fkey  | f
+ fk_notpartitioned_fk_a_b_fkey1 | f
+(2 rows)
+
+ALTER TABLE fk_notpartitioned_fk VALIDATE CONSTRAINT fk_notpartitioned_fk_a_b_fkey;
+-- All constraints are now valid.
+SELECT conname, convalidated FROM pg_constraint WHERE conrelid = 'fk_notpartitioned_fk'::regclass;
+            conname             | convalidated 
+--------------------------------+--------------
+ fk_notpartitioned_fk_a_b_fkey  | t
+ fk_notpartitioned_fk_a_b_fkey1 | t
+(2 rows)
+
+DROP TABLE fk_notpartitioned_fk, fk_partitioned_pk;
 -- Creation of a partitioned hierarchy with irregular definitions
 CREATE TABLE fk_notpartitioned_pk (fdrop1 int, a int, fdrop2 int, b int,
   PRIMARY KEY (a, b));
@@ -1597,12 +1688,6 @@ ALTER TABLE fk_partitioned_fk ATTACH PARTITION fk_partitioned_fk_3
 ALTER TABLE ONLY fk_partitioned_fk ADD FOREIGN KEY (a, b)
   REFERENCES fk_notpartitioned_pk;
 ERROR:  cannot use ONLY for foreign key on partitioned table "fk_partitioned_fk" referencing relation "fk_notpartitioned_pk"
--- Adding a NOT VALID foreign key on a partitioned table referencing
--- a non-partitioned table fails.
-ALTER TABLE fk_partitioned_fk ADD FOREIGN KEY (a, b)
-  REFERENCES fk_notpartitioned_pk NOT VALID;
-ERROR:  cannot add NOT VALID foreign key on partitioned table "fk_partitioned_fk" referencing relation "fk_notpartitioned_pk"
-DETAIL:  This feature is not yet supported on partitioned tables.
 -- these inserts, targeting both the partition directly as well as the
 -- partitioned table, should all fail
 INSERT INTO fk_partitioned_fk (a,b) VALUES (500, 501);