code: def ack_deadline(self):
          
          target = min([self._last_histogram_size * 2, self._last_histogram_size + 100])
          if len(self.ack_histogram) > target:
              self._ack_deadline = self.ack_histogram.percentile(percent=99)
          return self._ack_deadline
docs: Return the current ack deadline based on historical time-to-ack.
  
          This method is "sticky". It will only perform the computations to
          check on the right ack deadline if the histogram has gained a
          significant amount of new information.
  
          Returns:
              int: The ack deadline.