def _get_key_value(self, key, is_hll=False):
        '''
        Returns the proper key value for the stats
        @param key: the redis key
        @param is_hll: the key is a HyperLogLog, else is a sorted set
        '''
        if is_hll:
            return self.redis_conn.execute_command("PFCOUNT", key)
        else:
            return self.redis_conn.zcard(key)