diff --git a/internal/querynode/collection_replica.go b/internal/querynode/collection_replica.go
index cc63239189..190170c4b4 100644
--- a/internal/querynode/collection_replica.go
+++ b/internal/querynode/collection_replica.go
@@ -48,6 +48,7 @@ type ReplicaInterface interface {
 	getCollectionIDs() []UniqueID
 	addCollection(collectionID UniqueID, schema *schemapb.CollectionSchema) error
 	removeCollection(collectionID UniqueID) error
+	// getCollectionByID gets the collection which id is collectionID
 	getCollectionByID(collectionID UniqueID) (*Collection, error)
 	hasCollection(collectionID UniqueID) bool
 	getCollectionNum() int