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 delete_snapshot_metadata_item(self, snapshot_id, id):
        """Delete metadata item for the snapshot."""
        url = "snapshots/%s/metadata/%s" % (str(snapshot_id), str(id))
        resp, body = self.delete(url)
        return resp, body