code: def _GetUnsortedNotifications(self,
                                  queue_shard,
                                  notifications_by_session_id=None):
      if notifications_by_session_id is None:
        notifications_by_session_id = {}
      end_time = self.frozen_timestamp or rdfvalue.RDFDatetime.Now()
      for notification in self.data_store.GetNotifications(queue_shard, end_time):
        existing = notifications_by_session_id.get(notification.session_id)
        if existing:
          if notification.first_queued > existing.first_queued:
            notifications_by_session_id[notification.session_id] = notification
          elif notification.first_queued == existing.first_queued and (
              notification.last_status > existing.last_status):
            logging.warning(
                "Notifications with equal first_queued fields detected: %s %s",
                notification, existing)
            notifications_by_session_id[notification.session_id] = notification
        else:
          notifications_by_session_id[notification.session_id] = notification
      return notifications_by_session_id