code: func NotifyFlush(dom *domain.Domain, pluginName string) error {
  	p := getByName(pluginName)
  	if p == nil || p.Manifest.flushWatcher == nil || p.State != Ready {
  		return errors.Errorf("plugin %s doesn't exists or unsupported flush or doesn't start with PD", pluginName)
  	}
  	_, err := dom.GetEtcdClient().KV.Put(context.Background(), p.Manifest.flushWatcher.path, "")
  	if err != nil {
  		return err
  	}
  	return nil
  }
docs: // NotifyFlush notify plugins to do flush logic.