diff --git a/internal/querynode/flow_graph_service_time_node.go b/internal/querynode/flow_graph_service_time_node.go
index 0f8bca958c..dfabfe9fa3 100644
--- a/internal/querynode/flow_graph_service_time_node.go
+++ b/internal/querynode/flow_graph_service_time_node.go
@@ -26,6 +26,7 @@ import (
 	"github.com/milvus-io/milvus/internal/util/flowgraph"
 )
 
+// serviceTimeNode is one of the nodes in delta flow graph
 type serviceTimeNode struct {
 	baseNode
 	collectionID      UniqueID