def tick_deltas
      unless @delta.empty?
        merge_to_db(@delta)
        @tick_delta.concat(@delta.values) if accumulate_tick_deltas
        @delta.clear
      end
      unless @new_delta.empty?
        # We allow @new_delta to contain duplicates but eliminate them here. We
        # can't just allow duplicate delta tuples because that might cause
        # spurious infinite delta processing loops.
        @new_delta.reject! {|key, val| self[key] == val}

        @delta = @new_delta
        @new_delta = {}
      end
      return !(@delta.empty?)
    end
def tick_deltas
      unless @delta.empty?
        merge_to_db(@delta)
        @tick_delta.concat(@delta.values) if accumulate_tick_deltas
        @delta.clear
      end
      unless @new_delta.empty?
        # We allow @new_delta to contain duplicates but eliminate them here. We
        # can't just allow duplicate delta tuples because that might cause
        # spurious infinite delta processing loops.
        @new_delta.reject! {|key, val| self[key] == val}

        @delta = @new_delta
        @new_delta = {}
      end
      return !(@delta.empty?)
    end
move deltas to on-disk storage, and new_deltas to deltas