def incr(self, key, by=1):
        """ :see::meth:RedisMap.incr """
        pipe = self._client.pipeline(transaction=False)
        pipe.incr(self.get_key(key), by)
        if key not in self:
            pipe.hincrby(self._bucket_key, self.key_prefix, 1)
        result = pipe.execute()
        return result[0]