diff --git a/pkg/event/define.go b/pkg/event/define.go
index 529d7e3..8921901 100644
--- a/pkg/event/define.go
+++ b/pkg/event/define.go
@@ -18,6 +18,7 @@ type EventWorkFunc func() (interface{}, error)
 type DriverInterface interface {
 	Get() *Event
 	Put(event *Event)
+	GetLength() int
 }
 
 type ProduceInterface interface {