diff --git a/src/backend/utils/cache/inval.c b/src/backend/utils/cache/inval.c
index 35df9be5e54..a0c49519977 100644
--- a/src/backend/utils/cache/inval.c
+++ b/src/backend/utils/cache/inval.c
@@ -497,7 +497,9 @@ AddRelcacheInvalidationMessage(InvalidationMsgsGroup *group,
 /*
  * Add a relsync inval entry
  *
- * We put these into the relcache subgroup for simplicity.
+ * We put these into the relcache subgroup for simplicity. This message is the
+ * same as AddRelcacheInvalidationMessage() except that it is for
+ * RelationSyncCache maintained by decoding plugin pgoutput.
  */
 static void
 AddRelsyncInvalidationMessage(InvalidationMsgsGroup *group,
@@ -505,11 +507,11 @@ AddRelsyncInvalidationMessage(InvalidationMsgsGroup *group,
 {
 	SharedInvalidationMessage msg;
 
-	/* Don't add a duplicate item */
-	/* We assume dbId need not be checked because it will never change */
+	/* Don't add a duplicate item. */
 	ProcessMessageSubGroup(group, RelCacheMsgs,
 						   if (msg->rc.id == SHAREDINVALRELSYNC_ID &&
-							   msg->rc.relId == relId)
+							   (msg->rc.relId == relId ||
+								msg->rc.relId == InvalidOid))
 						   return);
 
 	/* OK, add the item */
@@ -650,9 +652,9 @@ RegisterRelcacheInvalidation(InvalidationInfo *info, Oid dbId, Oid relId)
 }
 
 /*
- * RegisterRelcacheInvalidation
+ * RegisterRelsyncInvalidation
  *
- * As above, but register a relsync invalidation event.
+ * As above, but register a relsynccache invalidation event.
  */
 static void
 RegisterRelsyncInvalidation(InvalidationInfo *info, Oid dbId, Oid relId)
@@ -660,7 +662,6 @@ RegisterRelsyncInvalidation(InvalidationInfo *info, Oid dbId, Oid relId)
 	AddRelsyncInvalidationMessage(&info->CurrentCmdInvalidMsgs, dbId, relId);
 }
 
-
 /*
  * RegisterSnapshotInvalidation
  *
@@ -1684,9 +1685,8 @@ CacheInvalidateRelcacheByRelid(Oid relid)
 	ReleaseSysCache(tup);
 }
 
-
 /*
- * RelationCacheInvalidate
+ * CacheInvalidateRelSync
  *		Register invalidation of the cache in logical decoding output plugin
  *		for a database.
  *
@@ -1701,7 +1701,6 @@ CacheInvalidateRelSync(Oid relid)
 								MyDatabaseId, relid);
 }
 
-
 /*
  * CacheInvalidateRelSyncAll
  *		Register invalidation of the whole cache in logical decoding output
@@ -1713,7 +1712,6 @@ CacheInvalidateRelSyncAll(void)
 	CacheInvalidateRelSync(InvalidOid);
 }
 
-
 /*
  * CacheInvalidateSmgr
  *		Register invalidation of smgr references to a physical relation.
@@ -1858,7 +1856,7 @@ CacheRegisterRelcacheCallback(RelcacheCallbackFunction func,
 /*
  * CacheRegisterRelSyncCallback
  *		Register the specified function to be called for all future
- *		decoding-cache invalidation events.
+ *		decoding plugin's relation cache invalidation events.
  *
  * This function is intended to be call from the logical decoding output
  * plugins.
diff --git a/src/include/storage/sinval.h b/src/include/storage/sinval.h
index 90a5af4ed8f..f168b5fbf8c 100644
--- a/src/include/storage/sinval.h
+++ b/src/include/storage/sinval.h
@@ -27,7 +27,7 @@
  *	* invalidate an smgr cache entry for a specific physical relation
  *	* invalidate the mapped-relation mapping for a given database
  *	* invalidate any saved snapshot that might be used to scan a given relation
- *	* invalidate a specific entry for specific output plugin
+ *	* invalidate a RelationSyncCache entry for a specific relation
  * More types could be added if needed.  The message type is identified by
  * the first "int8" field of the message struct.  Zero or positive means a
  * specific-catcache inval message (and also serves as the catcache ID field).
@@ -47,12 +47,12 @@
  * catcache inval messages must be generated for each of its caches, since
  * the hash keys will generally be different.
  *
- * Catcache, relcache, and snapshot invalidations are transactional, and so
- * are sent to other backends upon commit.  Internally to the generating
- * backend, they are also processed at CommandCounterIncrement so that later
- * commands in the same transaction see the new state.  The generating backend
- * also has to process them at abort, to flush out any cache state it's loaded
- * from no-longer-valid entries.
+ * Catcache, relcache, relsynccache, and snapshot invalidations are
+ * transactional, and so are sent to other backends upon commit.  Internally
+ * to the generating backend, they are also processed at
+ * CommandCounterIncrement so that later commands in the same transaction see
+ * the new state.  The generating backend also has to process them at abort,
+ * to flush out any cache state it's loaded from no-longer-valid entries.
  *
  * smgr and relation mapping invalidations are non-transactional: they are
  * sent immediately when the underlying file change is made.
@@ -117,7 +117,7 @@ typedef struct
 {
 	int8		id;				/* type field --- must be first */
 	Oid			dbId;			/* database ID */
-	Oid			relid;			/* relation ID, or 0 if whole relcache */
+	Oid			relid;			/* relation ID, or 0 if whole RelationSyncCache */
 } SharedInvalRelSyncMsg;
 
 typedef union