def link(self, bucket='_', tag='_', keep=False):
        """
        Add a link phase to the map/reduce operation.

        :param bucket: Bucket name (default '_', which means all
            buckets)
        :type bucket: string
        :param tag:  Tag (default '_', which means any tag)
        :type tag: string
        :param keep: Flag whether to keep results from this stage in
          the map/reduce. (default False, unless this is the last step
          in the phase)
        :type keep: boolean
        :rtype: :class:`RiakMapReduce`
        """
        self._phases.append(RiakLinkPhase(bucket, tag, keep))
        return self
Add a link phase to the map/reduce operation.

        :param bucket: Bucket name (default '_', which means all
            buckets)
        :type bucket: string
        :param tag:  Tag (default '_', which means any tag)
        :type tag: string
        :param keep: Flag whether to keep results from this stage in
          the map/reduce. (default False, unless this is the last step
          in the phase)
        :type keep: boolean
        :rtype: :class:`RiakMapReduce`