Log successful submissions

server.go

@@ -218,6 +218,7 @@ func (s *Server) handleSubmission(w http.ResponseWriter, r *http.Request) {
 		http.Error(w, err.Error(), http.StatusInternalServerError)
 		return
 	}
+	log.Printf("received %d entries from shard %s", len(req.Entries), req.Shard)
 
 	serverutil.EncodeJSONResponse(w, nil)
 }