def get_last_tid(self):
        try:
            spec = {'tid': {'$gt': 0}}
            sort = [('tid', -1)]
            row = self.db.docs.find_one(spec, sort=sort)
        except Exception as e:
            raise DatabaseException(e)
        if row:
            return row['tid']
        return 0
def get_clusters(self):
        """!
        @return (list) Allocated clusters where each cluster is represented by list of indexes of points from dataset,
                        for example, two cluster may have following representation [[0, 1, 4], [2, 3, 5, 6]].