def refresh(self, key, ttl, prev_value=None, prev_index=None,
                timeout=None):
        """Sets only a TTL of a key.  The waiters doesn't receive notification
        by this operation.
        """
        return self.adapter.set(key, ttl=ttl, refresh=True,
                                prev_value=prev_value, prev_index=prev_index,
                                timeout=timeout)
Sets only a TTL of a key.  The waiters doesn't receive notification
        by this operation.