diff --git a/internal/querynode/flow_graph_message.go b/internal/querynode/flow_graph_message.go
index d43a04e3ae..e56fa87a7a 100644
--- a/internal/querynode/flow_graph_message.go
+++ b/internal/querynode/flow_graph_message.go
@@ -16,7 +16,10 @@ import (
 	"github.com/milvus-io/milvus/internal/util/flowgraph"
 )
 
+// Msg is an interface which has a function named TimeTick
 type Msg = flowgraph.Msg
+
+// MsgStreamMsg is an implementation of interface Msg
 type MsgStreamMsg = flowgraph.MsgStreamMsg
 
 type insertMsg struct {