If the articles have some reasonably dense small IDs associated with them, then an easy algorithm is to simply pick a random ID between 0 and the max, check if

If the articles have some reasonably dense small IDs associated with them, then an easy algorithm is to simply pick a random ID between 0 and the max, check if it's a still-existing article, and repeat if not. There are plenty of distributed queue designs capable of distributing IDs to servers so they can be given to new articles, and re-using the id from a deleted article is fine to keep things denser.