diff --git a/docs/developer_guides/chap04_message_stream.md b/docs/developer_guides/chap04_message_stream.md
index 117cfe9ca0..69d8d4b2a8 100644
--- a/docs/developer_guides/chap04_message_stream.md
+++ b/docs/developer_guides/chap04_message_stream.md
@@ -164,6 +164,7 @@ type TsMsg interface {
 	BeginTs() Timestamp
 	EndTs() Timestamp
 	Type() MsgType
+	SourceID() int64
 	HashKeys() []uint32
 	Marshal(TsMsg) (MarshalType, error)
 	Unmarshal(MarshalType) (TsMsg, error)