Helper for :meth:`__iter__`.

def _on_error(self, exc):
        """Helper for :meth:`__iter__`."""
        # restart the read scan from AFTER the last successfully read row
        retry_request = self.request
        if self.last_scanned_row_key:
            retry_request = self._create_retry_request()

        self.response_iterator = self.read_method(retry_request)