diff --git a/internal/querynode/historical.go b/internal/querynode/historical.go
index d2ca5f024c..f8590e5b9f 100644
--- a/internal/querynode/historical.go
+++ b/internal/querynode/historical.go
@@ -36,6 +36,7 @@ const (
 	segmentMetaPrefix = "queryCoord-segmentMeta"
 )
 
+// historical is in charge of historical data in query node
 type historical struct {
 	ctx context.Context