Add new GUC disable_logical_replication_subscribers (#567)

Author: lubennikovaav

src/backend/replication/logical/launcher.c

@@ -51,6 +51,8 @@ int			max_logical_replication_workers = 4;
 int			max_sync_workers_per_subscription = 2;
 int			max_parallel_apply_workers_per_subscription = 2;
 
+bool disable_logical_replication_subscribers = false; /* NEON: GUC is defined in neon extension */
+
 LogicalRepWorker *MyLogicalRepWorker = NULL;
 
 typedef struct LogicalRepCtxStruct
@@ -343,6 +345,15 @@ logicalrep_worker_launch(LogicalRepWorkerType wtype,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("cannot start logical replication workers when \"max_active_replication_origins\" is 0")));
 
+	/* NEON GUC that allows to control logical replication without postgres restart */
+	if (disable_logical_replication_subscribers)
+	{
+		ereport(WARNING,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("cannot start logical replication workers when disable_logical_replication_subscribers=true")));
+		return false;
+	}
+
 	/*
 	 * We need to do the modification of the shared memory under lock so that
 	 * we have consistent view.

src/include/replication/logicallauncher.h

@@ -16,6 +16,8 @@ extern PGDLLIMPORT int max_logical_replication_workers;
 extern PGDLLIMPORT int max_sync_workers_per_subscription;
 extern PGDLLIMPORT int max_parallel_apply_workers_per_subscription;
 
+extern PGDLLIMPORT bool disable_logical_replication_subscribers;
+
 extern void ApplyLauncherRegister(void);
 extern void ApplyLauncherMain(Datum main_arg);