docs: public Deferred<ArrayList<Object>> flush() {
      final int size = size();
      if (size > 0) {
        LOG.info("Flushing all old outstanding rows out of " + size + " rows");
      }
      final long now = System.currentTimeMillis();
      return flush(now / 1000 - Const.MAX_TIMESPAN - 1, Integer.MAX_VALUE);
    }