def set_id(self, id='$'):
        """
        Set the last-read message id for each stream in the consumer group. By
        default, this will be the special "$" identifier, meaning all messages
        are marked as having been read.

        :param id: id of last-read message (or "$").
        """
        accum = {}
        for key in self.keys:
            accum[key] = self.database.xgroup_setid(key, self.name, id)
        return accum