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 split(root, minRight):
    if root is None:
        return None, None
    if root.key >= minRight:
        left, right = split(root.left, minRight)
        root.left = right
        root.update()
        return left, root
    else:
        left, right = split(root.right, minRight)
        root.right = left
        root.update()
        return root, right