Have ALTER CONSTRAINT recurse on partitioned tables

When ALTER TABLE .. ALTER CONSTRAINT changes deferrability properties
changed in a partitioned table, we failed to propagate those changes
correctly to partitions and to triggers.  Repair by adding a recursion
mechanism to affect all derived constraints and all derived triggers.
(In particular, recurse to partitions even if their respective parents
are already in the desired state: it is possible for the partitions to
have been altered individually.)  Because foreign keys involve tables in
two sides, we cannot use the standard ALTER TABLE recursion mechanism,
so we invent our own by following pg_constraint.conparentid down.

When ALTER TABLE .. ALTER CONSTRAINT is invoked on the derived
pg_constraint object that's automaticaly created in a partition as a
result of a constraint added to its parent, raise an error instead of
pretending to work and then failing to modify all the affected triggers.
Before this commit such a command would be allowed but failed to affect
all triggers, so it would silently misbehave.  (Restoring dumps of
existing databases is not affected, because pg_dump does not produce
anything for such a derived constraint anyway.)

Add some tests for the case.

Backpatch to 11, where foreign key support was added to partitioned
tables by commit 3de241dba86f.  (A related change is commit f56f8f8da6af
in pg12 which added support for FKs *referencing* partitioned tables;
this is what forces us to use an ad-hoc recursion mechanism for this.)

Diagnosed by Tom Lane from bug report from Ron L Johnson.  As of this
writing, no reviews were offered.

Discussion: https://postgr.es/m/75fe0761-a291-86a9-c8d8-4906da077469@gmail.com
Discussion: https://postgr.es/m/3144850.1607369633@sss.pgh.pa.us

1 files changed, 154 insertions, 34 deletions

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index a149ca044c1..95308db67ea 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -322,6 +322,9 @@ static void AlterSeqNamespaces(Relation classRel, Relation rel,
 				   LOCKMODE lockmode);
 static ObjectAddress ATExecAlterConstraint(Relation rel, AlterTableCmd *cmd,
 					  bool recurse, bool recursing, LOCKMODE lockmode);
+static bool ATExecAlterConstrRecurse(Constraint *cmdcon, Relation conrel,
+						 Relation tgrel, Relation rel, HeapTuple contuple,
+						 List **otherrelids, LOCKMODE lockmode);
 static ObjectAddress ATExecValidateConstraint(List **wqueue, Relation rel,
 						 char *constrName, bool recurse, bool recursing,
 						 LOCKMODE lockmode);
@@ -3953,6 +3956,7 @@ ATPrepCmd(List **wqueue, Relation rel, AlterTableCmd *cmd,
 			break;
 		case AT_AlterConstraint:	/* ALTER CONSTRAINT */
 			ATSimplePermissions(rel, ATT_TABLE);
+			/* Recursion occurs during execution phase */
 			pass = AT_PASS_MISC;
 			break;
 		case AT_ValidateConstraint: /* VALIDATE CONSTRAINT */
@@ -8311,28 +8315,29 @@ CloneFkReferencing(Relation pg_constraint, Relation parentRel,
  * Update the attributes of a constraint.
  *
  * Currently only works for Foreign Key constraints.
- * Foreign keys do not inherit, so we purposely ignore the
- * recursion bit here, but we keep the API the same for when
- * other constraint types are supported.
  *
  * If the constraint is modified, returns its address; otherwise, return
  * InvalidObjectAddress.
  */
 static ObjectAddress
-ATExecAlterConstraint(Relation rel, AlterTableCmd *cmd,
-					  bool recurse, bool recursing, LOCKMODE lockmode)
+ATExecAlterConstraint(Relation rel, AlterTableCmd *cmd, bool recurse,
+					  bool recursing, LOCKMODE lockmode)
 {
 	Constraint *cmdcon;
 	Relation	conrel;
+	Relation	tgrel;
 	SysScanDesc scan;
 	ScanKeyData skey[3];
 	HeapTuple	contuple;
 	Form_pg_constraint currcon;
 	ObjectAddress address;
+	List	   *otherrelids = NIL;
+	ListCell   *lc;
 
 	cmdcon = castNode(Constraint, cmd->def);
 
 	conrel = heap_open(ConstraintRelationId, RowExclusiveLock);
+	tgrel = heap_open(TriggerRelationId, RowExclusiveLock);
 
 	/*
 	 * Find and check the target constraint
@@ -8366,17 +8371,118 @@ ATExecAlterConstraint(Relation rel, AlterTableCmd *cmd,
 				 errmsg("constraint \"%s\" of relation \"%s\" is not a foreign key constraint",
 						cmdcon->conname, RelationGetRelationName(rel))));
 
+	/*
+	 * If it's not the topmost constraint, raise an error.
+	 *
+	 * Altering a non-topmost constraint leaves some triggers untouched, since
+	 * they are not directly connected to this constraint; also, pg_dump would
+	 * ignore the deferrability status of the individual constraint, since it
+	 * only dumps topmost constraints.  Avoid these problems by refusing this
+	 * operation and telling the user to alter the parent constraint instead.
+	 */
+	if (OidIsValid(currcon->conparentid))
+	{
+		HeapTuple	tp;
+		Oid			parent = currcon->conparentid;
+		char	   *ancestorname = NULL;
+		char	   *ancestortable = NULL;
+
+		/* Loop to find the topmost constraint */
+		while (HeapTupleIsValid(tp = SearchSysCache1(CONSTROID, ObjectIdGetDatum(parent))))
+		{
+			Form_pg_constraint contup = (Form_pg_constraint) GETSTRUCT(tp);
+
+			/* If no parent, this is the constraint we want */
+			if (!OidIsValid(contup->conparentid))
+			{
+				ancestorname = pstrdup(NameStr(contup->conname));
+				ancestortable = get_rel_name(contup->conrelid);
+				ReleaseSysCache(tp);
+				break;
+			}
+
+			parent = contup->conparentid;
+			ReleaseSysCache(tp);
+		}
+
+		ereport(ERROR,
+				(errmsg("cannot alter constraint \"%s\" on relation \"%s\"",
+						cmdcon->conname, RelationGetRelationName(rel)),
+				 ancestorname && ancestortable ?
+				 errdetail("Constraint \"%s\" is derived from constraint \"%s\" of relation \"%s\".",
+						   cmdcon->conname, ancestorname, ancestortable) : 0,
+				 errhint("You may alter the constraint it derives from, instead.")));
+	}
+
+	/*
+	 * Do the actual catalog work.  We can skip changing if already in the
+	 * desired state, but not if a partitioned table: partitions need to be
+	 * processed regardless, in case they've had it locally changed.
+	 */
+	address = InvalidObjectAddress;
+	if (currcon->condeferrable != cmdcon->deferrable ||
+		currcon->condeferred != cmdcon->initdeferred ||
+		rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
+	{
+		if (ATExecAlterConstrRecurse(cmdcon, conrel, tgrel, rel, contuple,
+									 &otherrelids, lockmode))
+			ObjectAddressSet(address, ConstraintRelationId,
+							 HeapTupleGetOid(contuple));
+	}
+
+	/*
+	 * ATExecConstrRecurse already invalidated relcache for the relations
+	 * having the constraint itself; here we also invalidate for relations
+	 * that have any triggers that implement the constraint.
+	 */
+	foreach(lc, otherrelids)
+		CacheInvalidateRelcacheByRelid(lfirst_oid(lc));
+
+	systable_endscan(scan);
+
+	heap_close(conrel, RowExclusiveLock);
+	heap_close(tgrel, RowExclusiveLock);
+
+	return address;
+}
+
+/*
+ * Recursive subroutine of ATExecAlterConstraint.  Returns true if the
+ * constraint is altered.
+ *
+ * *otherrelids is appended OIDs of relations containing affected triggers.
+ *
+ * Note that we must recurse even when the values are correct, in case
+ * indirect descendants have had their constraints altered locally.
+ * (This could be avoided if we forbade altering constraints in partitions
+ * but existing releases don't do that.)
+ */
+static bool
+ATExecAlterConstrRecurse(Constraint *cmdcon, Relation conrel, Relation tgrel,
+						 Relation rel, HeapTuple contuple, List **otherrelids,
+						 LOCKMODE lockmode)
+{
+	Form_pg_constraint currcon;
+	Oid			conoid;
+	bool		changed = false;
+
+	currcon = (Form_pg_constraint) GETSTRUCT(contuple);
+	conoid = HeapTupleGetOid(contuple);
+
+	/*
+	 * Update pg_constraint with the flags from cmdcon.
+	 *
+	 * If called to modify a constraint that's already in the desired state,
+	 * silently do nothing.
+	 */
 	if (currcon->condeferrable != cmdcon->deferrable ||
 		currcon->condeferred != cmdcon->initdeferred)
 	{
 		HeapTuple	copyTuple;
-		HeapTuple	tgtuple;
 		Form_pg_constraint copy_con;
-		List	   *otherrelids = NIL;
+		HeapTuple	tgtuple;
 		ScanKeyData tgkey;
 		SysScanDesc tgscan;
-		Relation	tgrel;
-		ListCell   *lc;
 
 		/*
 		 * Now update the catalog, while we have the door open.
@@ -8391,25 +8497,26 @@ ATExecAlterConstraint(Relation rel, AlterTableCmd *cmd,
 								  HeapTupleGetOid(contuple), 0);
 
 		heap_freetuple(copyTuple);
+		changed = true;
+
+		/* Make new constraint flags visible to others */
+		CacheInvalidateRelcache(rel);
 
 		/*
 		 * Now we need to update the multiple entries in pg_trigger that
 		 * implement the constraint.
 		 */
-		tgrel = heap_open(TriggerRelationId, RowExclusiveLock);
-
 		ScanKeyInit(&tgkey,
 					Anum_pg_trigger_tgconstraint,
 					BTEqualStrategyNumber, F_OIDEQ,
 					ObjectIdGetDatum(HeapTupleGetOid(contuple)));
-
 		tgscan = systable_beginscan(tgrel, TriggerConstraintIndexId, true,
 									NULL, 1, &tgkey);
-
 		while (HeapTupleIsValid(tgtuple = systable_getnext(tgscan)))
 		{
 			Form_pg_trigger tgform = (Form_pg_trigger) GETSTRUCT(tgtuple);
 			Form_pg_trigger copy_tg;
+			HeapTuple	copyTuple;
 
 			/*
 			 * Remember OIDs of other relation(s) involved in FK constraint.
@@ -8418,8 +8525,8 @@ ATExecAlterConstraint(Relation rel, AlterTableCmd *cmd,
 			 * change, but let's be conservative.)
 			 */
 			if (tgform->tgrelid != RelationGetRelid(rel))
-				otherrelids = list_append_unique_oid(otherrelids,
-													 tgform->tgrelid);
+				*otherrelids = list_append_unique_oid(*otherrelids,
+													  tgform->tgrelid);
 
 			/*
 			 * Update deferrability of RI_FKey_noaction_del,
@@ -8447,32 +8554,45 @@ ATExecAlterConstraint(Relation rel, AlterTableCmd *cmd,
 		}
 
 		systable_endscan(tgscan);
+	}
 
-		heap_close(tgrel, RowExclusiveLock);
+	/*
+	 * If the referencing table is partitioned, we need to recurse and handle
+	 * every constraint that is a child of this one.
+	 *
+	 * (This assumes that the recurse flag is forcibly set for partitioned
+	 * tables, and not set for legacy inheritance, though we don't check for
+	 * that here.)
+	 */
+	if (rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
+	{
+		ScanKeyData pkey;
+		SysScanDesc pscan;
+		HeapTuple	childtup;
 
-		/*
-		 * Invalidate relcache so that others see the new attributes.  We must
-		 * inval both the named rel and any others having relevant triggers.
-		 * (At present there should always be exactly one other rel, but
-		 * there's no need to hard-wire such an assumption here.)
-		 */
-		CacheInvalidateRelcache(rel);
-		foreach(lc, otherrelids)
+		ScanKeyInit(&pkey,
+					Anum_pg_constraint_conparentid,
+					BTEqualStrategyNumber, F_OIDEQ,
+					ObjectIdGetDatum(conoid));
+
+		pscan = systable_beginscan(conrel, ConstraintParentIndexId,
+								   true, NULL, 1, &pkey);
+
+		while (HeapTupleIsValid(childtup = systable_getnext(pscan)))
 		{
-			CacheInvalidateRelcacheByRelid(lfirst_oid(lc));
+			Form_pg_constraint childcon = (Form_pg_constraint) GETSTRUCT(childtup);
+			Relation	childrel;
+
+			childrel = heap_open(childcon->conrelid, lockmode);
+			ATExecAlterConstrRecurse(cmdcon, conrel, tgrel, childrel, childtup,
+									 otherrelids, lockmode);
+			heap_close(childrel, NoLock);
 		}
 
-		ObjectAddressSet(address, ConstraintRelationId,
-						 HeapTupleGetOid(contuple));
+		systable_endscan(pscan);
 	}
-	else
-		address = InvalidObjectAddress;
 
-	systable_endscan(scan);
-
-	heap_close(conrel, RowExclusiveLock);
-
-	return address;
+	return changed;
 }
 
 /*