apollo-configservice/src/main/java/com/ctrip/framework/apollo/configservice/controller/NotificationControllerV2.java/NotificationControllerV2/logWatchedKeys
class NotificationControllerV2:  private void logWatchedKeys(Set<String> watchedKeys, String eventName) {
    for (String watchedKey : watchedKeys) {
      Tracer.logEvent(eventName, watchedKey);
    }
  }