diff --git a/internal/querynode/historical.go b/internal/querynode/historical.go
index d2ca5f024cea4e7b86d3e8841cc7f98fccda7b57..f8590e5b9f1f1e7026a673def7b2138aef1fc21a 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