code: def _adjust_delay(self, slot, response):
          
          if response.status in self.retry_http_codes:
              new_delay = max(slot.delay, 1) * 4
              new_delay = max(new_delay, self.mindelay)
              new_delay = min(new_delay, self.maxdelay)
              slot.delay = new_delay
              self.stats.inc_value('delay_count')
          elif response.status == 200:
              new_delay = max(slot.delay / 2, self.mindelay)
              if new_delay < 0.01:
                  new_delay = 0
              slot.delay = new_delay
docs: Define delay adjustment policy