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 create_snapshot_metadata(self, snapshot_id, metadata):
        """Create metadata for the snapshot."""
        put_body = json.dumps({'metadata': metadata})
        url = "snapshots/%s/metadata" % str(snapshot_id)
        resp, body = self.post(url, put_body)
        body = json.loads(body)
        return resp, body['metadata']