implement CanUseCoordinatorLocalTablesWithReferenceTables and refactor existing usages

src/backend/distributed/executor/multi_executor.c

@@ -752,28 +752,12 @@ IsLocalReferenceTableJoinPlan(PlannedStmt *plan)
 {
 	bool hasReferenceTable = false;
 	bool hasLocalTable = false;
-	bool hasReferenceTableReplica = false;
 
 	/*
-	 * We only allow join between reference tables and local tables in the
-	 * coordinator.
+	 * Check if we are in the coordinator and coordinator can have reference
+	 * table placements
 	 */
-	if (!IsCoordinator())
-	{
-		return false;
-	}
-
-	/*
-	 * All groups that have pg_dist_node entries, also have reference
-	 * table replicas.
-	 */
-	PrimaryNodeForGroup(GetLocalGroupId(), &hasReferenceTableReplica);
-
-	/*
-	 * If reference table doesn't have replicas on the coordinator, we don't
-	 * allow joins with local tables.
-	 */
-	if (!hasReferenceTableReplica)
+	if (!CanUseCoordinatorLocalTablesWithReferenceTables())
 	{
 		return false;
 	}

src/backend/distributed/master/worker_node_manager.c

@@ -17,6 +17,7 @@
 #include "commands/dbcommands.h"
 #include "distributed/hash_helpers.h"
 #include "distributed/listutils.h"
+#include "distributed/master_protocol.h"
 #include "distributed/metadata_cache.h"
 #include "distributed/multi_client_executor.h"
 #include "distributed/worker_manager.h"
@@ -402,6 +403,39 @@ NodeIsPrimaryWorker(WorkerNode *node)
 }
 
 
+/*
+ * CanUseCoordinatorLocalTablesWithReferenceTables returns true if we
+ * are allowed to use coordinator local tables with reference tables
+ * for joining or defining foreign keys between them.
+ */
+bool
+CanUseCoordinatorLocalTablesWithReferenceTables(void)
+{
+	/*
+	 * Using local tables of coordinator with reference tables is only allowed
+	 * if we are in the coordinator.
+	 *
+	 * Also, to check if coordinator can have reference table placements in below
+	 * check, we should be in the coordinator.
+	 */
+	if (!IsCoordinator())
+	{
+		return false;
+	}
+
+	/*
+	 * If reference table doesn't have placements on the coordinator, we don't
+	 * use local tables in coordinator with reference tables.
+	 */
+	if (!CanHaveReferenceTablePlacements())
+	{
+		return false;
+	}
+
+	return true;
+}
+
+
 /*
  * CanHaveReferenceTablePlacements returns true if current node can have
  * reference table placements. This is only possible if we called below

src/include/distributed/worker_manager.h

@@ -72,6 +72,7 @@ extern WorkerNode * WorkerGetLocalFirstCandidateNode(List *currentNodeList);
 extern uint32 ActivePrimaryWorkerNodeCount(void);
 extern List * ActivePrimaryWorkerNodeList(LOCKMODE lockMode);
 extern List * ActivePrimaryNodeList(LOCKMODE lockMode);
+extern bool CanUseCoordinatorLocalTablesWithReferenceTables(void);
 extern List * ReferenceTablePlacementNodeList(LOCKMODE lockMode);
 extern List * DistributedTablePlacementNodeList(LOCKMODE lockMode);
 extern bool NodeCanHaveDistTablePlacements(WorkerNode *node);