Avoid bogus scans of partitions when validating FKs to partitioned tables

Validating an unvalidated foreign key that references a partitioned
table would try to queue validations for each individual partition of
the referenced table, but this is wrong: each individual partition would
not necessarily have all the referenced rows, so errors would be raised.
Avoid doing that.  The pg_constraint rows that cause this to happen are
only there to support the action triggers that implement the DELETE/
UPDATE actions of the FK, so no validating scan is necessary.

This was an oversight in commit b663b9436e.

An equivalent oversight exists for NOT ENFORCED constraints, which is
not fixed in this commit.

Author: Amul Sul <sulamul@gmail.com>
Reported-by: Antonin Houska <ah@cybertec.at>
Reviewed-by: jian he <jian.universality@gmail.com>
Reviewed-by: Tender Wang <tndrwang@gmail.com>
Discussion: https://postgr.es/m/26983.1748418675@localhost

src/backend/commands/tablecmds.c

@@ -430,8 +430,8 @@ static void AlterConstrUpdateConstraintEntry(ATAlterConstraint *cmdcon, Relation
 static ObjectAddress ATExecValidateConstraint(List **wqueue,
 											  Relation rel, char *constrName,
 											  bool recurse, bool recursing, LOCKMODE lockmode);
-static void QueueFKConstraintValidation(List **wqueue, Relation conrel, Relation rel,
+static void QueueFKConstraintValidation(List **wqueue, Relation conrel, Relation fkrel,
-										HeapTuple contuple, LOCKMODE lockmode);
+										Oid pkrelid, HeapTuple contuple, LOCKMODE lockmode);
 static void QueueCheckConstraintValidation(List **wqueue, Relation conrel, Relation rel,
 										   char *constrName, HeapTuple contuple,
 										   bool recurse, bool recursing, LOCKMODE lockmode);
@@ -11858,6 +11858,7 @@ AttachPartitionForeignKey(List **wqueue,
 	if (queueValidation)
 	{
 		Relation	conrel;
+		Oid			confrelid;
 
 		conrel = table_open(ConstraintRelationId, RowExclusiveLock);
 
@@ -11865,9 +11866,11 @@ AttachPartitionForeignKey(List **wqueue,
 		if (!HeapTupleIsValid(partcontup))
 			elog(ERROR, "cache lookup failed for constraint %u", partConstrOid);
 
+		confrelid = ((Form_pg_constraint) GETSTRUCT(partcontup))->confrelid;
+
 		/* Use the same lock as for AT_ValidateConstraint */
-		QueueFKConstraintValidation(wqueue, conrel, partition, partcontup,
+		QueueFKConstraintValidation(wqueue, conrel, partition, confrelid,
-									ShareUpdateExclusiveLock);
+									partcontup, ShareUpdateExclusiveLock);
 		ReleaseSysCache(partcontup);
 		table_close(conrel, RowExclusiveLock);
 	}
@@ -12919,7 +12922,8 @@ ATExecValidateConstraint(List **wqueue, Relation rel, char *constrName,
 	{
 		if (con->contype == CONSTRAINT_FOREIGN)
 		{
-			QueueFKConstraintValidation(wqueue, conrel, rel, tuple, lockmode);
+			QueueFKConstraintValidation(wqueue, conrel, rel, con->confrelid,
+										tuple, lockmode);
 		}
 		else if (con->contype == CONSTRAINT_CHECK)
 		{
@@ -12952,8 +12956,8 @@ ATExecValidateConstraint(List **wqueue, Relation rel, char *constrName,
  * for the specified relation and all its children.
  */
 static void
-QueueFKConstraintValidation(List **wqueue, Relation conrel, Relation rel,
+QueueFKConstraintValidation(List **wqueue, Relation conrel, Relation fkrel,
-							HeapTuple contuple, LOCKMODE lockmode)
+							Oid pkrelid, HeapTuple contuple, LOCKMODE lockmode)
 {
 	Form_pg_constraint con;
 	AlteredTableInfo *tab;
@@ -12964,7 +12968,17 @@ QueueFKConstraintValidation(List **wqueue, Relation conrel, Relation rel,
 	Assert(con->contype == CONSTRAINT_FOREIGN);
 	Assert(!con->convalidated);
 
-	if (rel->rd_rel->relkind == RELKIND_RELATION)
+	/*
+	 * Add the validation to phase 3's queue; not needed for partitioned
+	 * tables themselves, only for their partitions.
+	 *
+	 * When the referenced table (pkrelid) is partitioned, the referencing
+	 * table (fkrel) has one pg_constraint row pointing to each partition
+	 * thereof.  These rows are there only to support action triggers and no
+	 * table scan is needed, therefore skip this for them as well.
+	 */
+	if (fkrel->rd_rel->relkind == RELKIND_RELATION &&
+		con->confrelid == pkrelid)
 	{
 		NewConstraint *newcon;
 		Constraint *fkconstraint;
@@ -12983,15 +12997,16 @@ QueueFKConstraintValidation(List **wqueue, Relation conrel, Relation rel,
 		newcon->qual = (Node *) fkconstraint;
 
 		/* Find or create work queue entry for this table */
-		tab = ATGetQueueEntry(wqueue, rel);
+		tab = ATGetQueueEntry(wqueue, fkrel);
 		tab->constraints = lappend(tab->constraints, newcon);
 	}
 
 	/*
 	 * 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.
+	 * recurse and handle every unvalidate constraint that is a child of this
+	 * constraint.
 	 */
-	if (rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE ||
+	if (fkrel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE ||
 		get_rel_relkind(con->confrelid) == RELKIND_PARTITIONED_TABLE)
 	{
 		ScanKeyData pkey;
@@ -13023,8 +13038,12 @@ QueueFKConstraintValidation(List **wqueue, Relation conrel, Relation rel,
 
 			childrel = table_open(childcon->conrelid, lockmode);
 
-			QueueFKConstraintValidation(wqueue, conrel, childrel, childtup,
+			/*
-										lockmode);
+			 * NB: Note that pkrelid should be passed as-is during recursion,
+			 * as it is required to identify the root referenced table.
+			 */
+			QueueFKConstraintValidation(wqueue, conrel, childrel, pkrelid,
+										childtup, lockmode);
 			table_close(childrel, NoLock);
 		}
 
@@ -13032,7 +13051,11 @@ QueueFKConstraintValidation(List **wqueue, Relation conrel, Relation rel,
 	}
 
 	/*
-	 * Now update the catalog, while we have the door open.
+	 * Now mark the pg_constraint row as validated (even if we didn't check,
+	 * notably the ones for partitions on the referenced side).
+	 *
+	 * We rely on transaction abort to roll back this change if phase 3
+	 * ultimately finds violating rows.  This is a bit ugly.
 	 */
 	copyTuple = heap_copytuple(contuple);
 	copy_con = (Form_pg_constraint) GETSTRUCT(copyTuple);

src/test/regress/expected/foreign_key.out

@@ -1895,29 +1895,67 @@ WHERE conrelid::regclass::text like 'fk_partitioned_fk%' ORDER BY oid::regclass:
 (5 rows)
 
 DROP TABLE fk_partitioned_fk, fk_notpartitioned_pk;
--- NOT VALID foreign key on a non-partitioned table referencing a partitioned table
+-- 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_partitioned_pk_2 PARTITION OF fk_partitioned_pk FOR VALUES FROM (1000,1000) TO (2000,2000);
 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;
+INSERT INTO fk_partitioned_pk VALUES(100,100), (1000,1000);
--- Constraint will be invalid.
+INSERT INTO fk_notpartitioned_fk VALUES(100,100), (1000,1000);
-SELECT conname, convalidated FROM pg_constraint
+ALTER TABLE fk_notpartitioned_fk ADD CONSTRAINT fk_notpartitioned_fk_a_b_fkey
+	FOREIGN KEY (a, b) REFERENCES fk_partitioned_pk NOT VALID;
+-- All constraints will be invalid.
+SELECT conname, conenforced, convalidated FROM pg_constraint
 WHERE conrelid = 'fk_notpartitioned_fk'::regclass ORDER BY oid::regclass::text;
-             conname             | convalidated 
+             conname             | conenforced | convalidated 
----------------------------------+--------------
+---------------------------------+-------------+--------------
- fk_notpartitioned_fk_a_b_fkey   | f
+ fk_notpartitioned_fk_a_b_fkey   | t           | f
- fk_notpartitioned_fk_a_b_fkey_1 | f
+ fk_notpartitioned_fk_a_b_fkey_1 | t           | f
-(2 rows)
+ fk_notpartitioned_fk_a_b_fkey_2 | t           | f
+(3 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
+SELECT conname, conenforced, convalidated FROM pg_constraint
 WHERE conrelid = 'fk_notpartitioned_fk'::regclass ORDER BY oid::regclass::text;
-             conname             | convalidated 
+             conname             | conenforced | convalidated 
----------------------------------+--------------
+---------------------------------+-------------+--------------
- fk_notpartitioned_fk_a_b_fkey   | t
+ fk_notpartitioned_fk_a_b_fkey   | t           | t
- fk_notpartitioned_fk_a_b_fkey_1 | t
+ fk_notpartitioned_fk_a_b_fkey_1 | t           | t
-(2 rows)
+ fk_notpartitioned_fk_a_b_fkey_2 | t           | t
+(3 rows)
+
+-- test a self-referential FK
+ALTER TABLE fk_partitioned_pk ADD CONSTRAINT selffk FOREIGN KEY (a, b) REFERENCES fk_partitioned_pk NOT VALID;
+CREATE TABLE fk_partitioned_pk_3 PARTITION OF fk_partitioned_pk FOR VALUES FROM (2000,2000) TO (3000,3000)
+  PARTITION BY RANGE (a);
+CREATE TABLE fk_partitioned_pk_3_1 PARTITION OF fk_partitioned_pk_3 FOR VALUES FROM (2000) TO (2100);
+SELECT conname, conenforced, convalidated FROM pg_constraint
+WHERE conrelid = 'fk_partitioned_pk'::regclass AND contype = 'f'
+ORDER BY oid::regclass::text;
+  conname   | conenforced | convalidated 
+------------+-------------+--------------
+ selffk     | t           | f
+ selffk_1   | t           | f
+ selffk_2   | t           | f
+ selffk_3   | t           | f
+ selffk_3_1 | t           | f
+(5 rows)
+
+ALTER TABLE fk_partitioned_pk_2 VALIDATE CONSTRAINT selffk;
+ALTER TABLE fk_partitioned_pk VALIDATE CONSTRAINT selffk;
+SELECT conname, conenforced, convalidated FROM pg_constraint
+WHERE conrelid = 'fk_partitioned_pk'::regclass AND contype = 'f'
+ORDER BY oid::regclass::text;
+  conname   | conenforced | convalidated 
+------------+-------------+--------------
+ selffk     | t           | t
+ selffk_1   | t           | t
+ selffk_2   | t           | t
+ selffk_3   | t           | t
+ selffk_3_1 | t           | t
+(5 rows)
 
 DROP TABLE fk_notpartitioned_fk, fk_partitioned_pk;
 -- Test some other exotic foreign key features: MATCH SIMPLE, ON UPDATE/DELETE

src/test/regress/sql/foreign_key.sql

@@ -1389,22 +1389,41 @@ WHERE conrelid::regclass::text like 'fk_partitioned_fk%' ORDER BY oid::regclass:
 
 DROP TABLE fk_partitioned_fk, fk_notpartitioned_pk;
 
--- NOT VALID foreign key on a non-partitioned table referencing a partitioned table
+-- 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_partitioned_pk_2 PARTITION OF fk_partitioned_pk FOR VALUES FROM (1000,1000) TO (2000,2000);
 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;
+INSERT INTO fk_partitioned_pk VALUES(100,100), (1000,1000);
+INSERT INTO fk_notpartitioned_fk VALUES(100,100), (1000,1000);
+ALTER TABLE fk_notpartitioned_fk ADD CONSTRAINT fk_notpartitioned_fk_a_b_fkey
+	FOREIGN KEY (a, b) REFERENCES fk_partitioned_pk NOT VALID;
 
--- Constraint will be invalid.
+-- All constraints will be invalid.
-SELECT conname, convalidated FROM pg_constraint
+SELECT conname, conenforced, convalidated FROM pg_constraint
 WHERE conrelid = 'fk_notpartitioned_fk'::regclass ORDER BY oid::regclass::text;
 
 ALTER TABLE fk_notpartitioned_fk VALIDATE CONSTRAINT fk_notpartitioned_fk_a_b_fkey;
 
 -- All constraints are now valid.
-SELECT conname, convalidated FROM pg_constraint
+SELECT conname, conenforced, convalidated FROM pg_constraint
 WHERE conrelid = 'fk_notpartitioned_fk'::regclass ORDER BY oid::regclass::text;
 
+-- test a self-referential FK
+ALTER TABLE fk_partitioned_pk ADD CONSTRAINT selffk FOREIGN KEY (a, b) REFERENCES fk_partitioned_pk NOT VALID;
+CREATE TABLE fk_partitioned_pk_3 PARTITION OF fk_partitioned_pk FOR VALUES FROM (2000,2000) TO (3000,3000)
+  PARTITION BY RANGE (a);
+CREATE TABLE fk_partitioned_pk_3_1 PARTITION OF fk_partitioned_pk_3 FOR VALUES FROM (2000) TO (2100);
+SELECT conname, conenforced, convalidated FROM pg_constraint
+WHERE conrelid = 'fk_partitioned_pk'::regclass AND contype = 'f'
+ORDER BY oid::regclass::text;
+ALTER TABLE fk_partitioned_pk_2 VALIDATE CONSTRAINT selffk;
+ALTER TABLE fk_partitioned_pk VALIDATE CONSTRAINT selffk;
+SELECT conname, conenforced, convalidated FROM pg_constraint
+WHERE conrelid = 'fk_partitioned_pk'::regclass AND contype = 'f'
+ORDER BY oid::regclass::text;
+
 DROP TABLE fk_notpartitioned_fk, fk_partitioned_pk;
 
 -- Test some other exotic foreign key features: MATCH SIMPLE, ON UPDATE/DELETE