Do not rely on fk cache when truncating local data (#5018)

src/backend/distributed/commands/foreign_constraint.c

@@ -734,8 +734,8 @@ HasForeignKeyWithLocalTable(Oid relationId)
 
 
 /*
- * GetForeignKeysWithLocalTables returns a list foreign keys for foreign key
+ * GetForeignKeysWithLocalTables returns a list of foreign keys for foreign key
- * relationaships that relation has with local tables.
+ * relationships that relation has with local tables.
  */
 static List *
 GetForeignKeysWithLocalTables(Oid relationId)
@@ -753,6 +753,21 @@ GetForeignKeysWithLocalTables(Oid relationId)
 }
 
 
+/*
+ * GetForeignKeysFromLocalTables returns a list of foreign keys where the referencing
+ * relation is a local table.
+ */
+List *
+GetForeignKeysFromLocalTables(Oid relationId)
+{
+	int referencedFKeysFlag = INCLUDE_REFERENCED_CONSTRAINTS |
+							  INCLUDE_LOCAL_TABLES;
+	List *referencingFKeyList = GetForeignKeyOids(relationId, referencedFKeysFlag);
+
+	return referencingFKeyList;
+}
+
+
 /*
  * HasForeignKeyToCitusLocalTable returns true if any of the foreign key constraints
  * on the relation with relationId references to a citus local table.
@@ -1102,6 +1117,30 @@ GetReferencedTableId(Oid foreignKeyId)
 }
 
 
+/*
+ * GetReferencingTableId returns OID of the referencing relation for the foreign
+ * key with foreignKeyId. If there is no such foreign key, then this function
+ * returns InvalidOid.
+ */
+Oid
+GetReferencingTableId(Oid foreignKeyId)
+{
+	HeapTuple heapTuple = SearchSysCache1(CONSTROID, ObjectIdGetDatum(foreignKeyId));
+	if (!HeapTupleIsValid(heapTuple))
+	{
+		/* no such foreign key */
+		return InvalidOid;
+	}
+
+	Form_pg_constraint constraintForm = (Form_pg_constraint) GETSTRUCT(heapTuple);
+	Oid referencingTableId = constraintForm->conrelid;
+
+	ReleaseSysCache(heapTuple);
+
+	return referencingTableId;
+}
+
+
 /*
  * IsTableTypeIncluded returns true if type of the table with relationId (distributed,
  * reference, Citus local or Postgres local) is included in the flags, false if not

src/backend/distributed/commands/truncate.c

@@ -217,16 +217,12 @@ EnsureLocalTableCanBeTruncated(Oid relationId)
 								  "tables.")));
 	}
 
-	/* make sure there are no foreign key references from a local table */
+	List *referencingForeignConstaintsFromLocalTables =
-	SetForeignConstraintRelationshipGraphInvalid();
+		GetForeignKeysFromLocalTables(relationId);
-	List *referencingRelationList = ReferencingRelationIdList(relationId);
+	if (list_length(referencingForeignConstaintsFromLocalTables) > 0)
-
-	Oid referencingRelation = InvalidOid;
-	foreach_oid(referencingRelation, referencingRelationList)
-	{
-		/* we do not truncate a table if there is a local table referencing it */
-		if (!IsCitusTable(referencingRelation))
 	{
+		Oid foreignKeyId = linitial_oid(referencingForeignConstaintsFromLocalTables);
+		Oid referencingRelation = GetReferencingTableId(foreignKeyId);
 		char *referencedRelationName = get_rel_name(relationId);
 		char *referencingRelationName = get_rel_name(referencingRelation);
 
@@ -236,7 +232,6 @@ EnsureLocalTableCanBeTruncated(Oid relationId)
 								  referencingRelationName,
 								  referencedRelationName)));
 	}
-	}
 }
 
 

src/include/distributed/commands.h

@@ -207,6 +207,7 @@ extern bool AnyForeignKeyDependsOnIndex(Oid indexId);
 extern bool HasForeignKeyWithLocalTable(Oid relationId);
 extern bool HasForeignKeyToCitusLocalTable(Oid relationId);
 extern bool HasForeignKeyToReferenceTable(Oid relationOid);
+extern List * GetForeignKeysFromLocalTables(Oid relationId);
 extern bool TableReferenced(Oid relationOid);
 extern bool TableReferencing(Oid relationOid);
 extern bool ConstraintIsAUniquenessConstraint(char *inputConstaintName, Oid relationId);
@@ -217,6 +218,7 @@ extern bool ConstraintWithIdIsOfType(Oid constraintId, char targetConstraintType
 extern bool TableHasExternalForeignKeys(Oid relationId);
 extern List * GetForeignKeyOids(Oid relationId, int flags);
 extern Oid GetReferencedTableId(Oid foreignKeyId);
+extern Oid GetReferencingTableId(Oid foreignKeyId);
 extern bool RelationInvolvedInAnyNonInheritedForeignKeys(Oid relationId);