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