def list_completeness_index(self, start=None, stop=None):
        params = {}
        if start is not None:
            params['start'] = to_isostring(start)
        if stop is not None:
            params['stop'] = to_isostring(stop)
        return pagination.Iterator(
            client=self._client,
            path='/archive/{}/completeness-index'.format(self._instance),
            params=params,
            response_class=archive_pb2.IndexResponse,
            items_key='group',
            item_mapper=IndexGroup,
        )