code: def notify_rollover(self, stream):
          
  
          self.offset -= 1
  
          if not self.matches(stream):
              return
  
          if self._count == 0:
              raise InternalError("BufferedStreamWalker out of sync with storage engine, count was wrong.")
  
          self._count -= 1
docs: Notify that a reading in the given stream was overwritten.
  
          Args:
              stream (DataStream): The stream that had overwritten data.