def update_sibling_distance(self, sibling_distance, dest, topic):
        """Update the sibling distance for topic and destination broker."""
        for source in six.iterkeys(sibling_distance[dest]):
            sibling_distance[dest][source][topic] = \
                dest.count_partitions(topic) - \
                source.count_partitions(topic)
        return sibling_distance
Update the sibling distance for topic and destination broker.