def update(self, data):
        """ :see::meth:RedisMap.update """
        result = None
        if data:
            pipe = self._client.pipeline(transaction=False)
            for k in data.keys():
                pipe.exists(self.get_key(k))
            exists = pipe.execute()
            exists = exists.count(True)
            _rk, _dumps = self.get_key, self._dumps
            data = {
                _rk(key): _dumps(value)
                for key, value in data.items()}
            pipe.mset(data)
            pipe.hincrby(self._bucket_key, self.key_prefix, len(data)-exists)
            result = pipe.execute()[0]
        return result
:see::meth:RedisMap.update