func (n *node) recoverAndclean() {
	if n.IsDir() {
		for _, child := range n.Children {
			child.Parent = n
			child.store = n.store
			child.recoverAndclean()
		}
	}

	if !n.ExpireTime.IsZero() {
		n.store.ttlKeyHeap.push(n)
	}
}
func (n *node) recoverAndclean() {
	if n.IsDir() {
		for _, child := range n.Children {
			child.Parent = n
			child.store = n.store
			child.recoverAndclean()
		}
	}

	if !n.ExpireTime.IsZero() {
		n.store.ttlKeyHeap.push(n)
	}
}
// recoverAndclean function help to do recovery.
// Two things need to be done: 1. recovery structure; 2. delete expired nodes
//
// If the node is a directory, it will help recover children's parent pointer and recursively
// call this function on its children.
// We check the expire last since we need to recover the whole structure first and add all the
// notifications into the event history.