Allow metadata sync functions on secondaries

{start,stop}_metadata_sync_to_node now toggle the hasMetadata flag when
run on secondaries but don't attempt to actually sync any metadata.

src/backend/distributed/metadata/metadata_sync.c

@@ -111,6 +111,15 @@ start_metadata_sync_to_node(PG_FUNCTION_ARGS)
 
 	MarkNodeHasMetadata(nodeNameString, nodePort, true);
 
+	if (!WorkerNodeIsPrimary(workerNode))
+	{
+		/*
+		 * If this is a secondary node we can't actually sync metadata to it; we assume
+		 * the primary node is receiving metadata.
+		 */
+		PG_RETURN_VOID();
+	}
+
 	/* generate and add the local group id's update query */
 	localGroupIdUpdateCommand = LocalGroupIdUpdateCommand(workerNode->groupId);
 

src/test/regress/expected/multi_metadata_sync.out

@@ -175,6 +175,38 @@ SELECT count(*) FROM pg_dist_node WHERE hasmetadata=true;
      0
 (1 row)
 
+-- Ensure it works when run on a secondary node
+SELECT groupid AS worker_1_group FROM pg_dist_node WHERE nodeport = :worker_1_port \gset
+SELECT master_add_node('localhost', 8888, groupid => :worker_1_group, noderole => 'secondary');
+              master_add_node               
+--------------------------------------------
+ (4,1,localhost,8888,default,f,t,secondary)
+(1 row)
+
+SELECT start_metadata_sync_to_node('localhost', 8888);
+ start_metadata_sync_to_node 
+-----------------------------
+ 
+(1 row)
+
+SELECT hasmetadata FROM pg_dist_node WHERE nodeport = 8888;
+ hasmetadata 
+-------------
+ t
+(1 row)
+
+SELECT stop_metadata_sync_to_node('localhost', 8888);
+ stop_metadata_sync_to_node 
+----------------------------
+ 
+(1 row)
+
+SELECT hasmetadata FROM pg_dist_node WHERE nodeport = 8888;
+ hasmetadata 
+-------------
+ f
+(1 row)
+
 -- Run start_metadata_sync_to_node and check that it marked hasmetadata for that worker
 SELECT start_metadata_sync_to_node('localhost', :worker_1_port);
  start_metadata_sync_to_node 
@@ -1131,7 +1163,7 @@ SELECT create_distributed_table('mx_table', 'a');
 SELECT master_add_node('localhost', :worker_2_port);
               master_add_node              
 -------------------------------------------
- (4,4,localhost,57638,default,f,t,primary)
+ (5,4,localhost,57638,default,f,t,primary)
 (1 row)
 
 SELECT start_metadata_sync_to_node('localhost', :worker_2_port);
@@ -1344,7 +1376,7 @@ SELECT master_add_node('localhost', :worker_2_port);
 NOTICE:  Replicating reference table "mx_ref" to the node localhost:57638
               master_add_node              
 -------------------------------------------
- (5,5,localhost,57638,default,f,t,primary)
+ (6,5,localhost,57638,default,f,t,primary)
 (1 row)
 
 SELECT shardid, nodename, nodeport 

src/test/regress/sql/multi_metadata_sync.sql

@@ -67,6 +67,14 @@ SELECT unnest(master_metadata_snapshot());
 -- Ensure that hasmetadata=false for all nodes
 SELECT count(*) FROM pg_dist_node WHERE hasmetadata=true;
 
+-- Ensure it works when run on a secondary node
+SELECT groupid AS worker_1_group FROM pg_dist_node WHERE nodeport = :worker_1_port \gset
+SELECT master_add_node('localhost', 8888, groupid => :worker_1_group, noderole => 'secondary');
+SELECT start_metadata_sync_to_node('localhost', 8888);
+SELECT hasmetadata FROM pg_dist_node WHERE nodeport = 8888;
+SELECT stop_metadata_sync_to_node('localhost', 8888);
+SELECT hasmetadata FROM pg_dist_node WHERE nodeport = 8888;
+
 -- Run start_metadata_sync_to_node and check that it marked hasmetadata for that worker
 SELECT start_metadata_sync_to_node('localhost', :worker_1_port);
 SELECT nodeid, hasmetadata FROM pg_dist_node WHERE nodename='localhost' AND nodeport=:worker_1_port;