I’ve noticed that all posts bear both a post_id and a post_number. I understand that post_id is the unique identifier of the post in the entire forum, while post_number is the number of the post in its topic. Posts identify themselves as replies to other posts by referencing the post_number of another post in the reply_to_post_number field. Whenever any topic (or section of posts from a topic) is retrieved from the server, it contains a sorted array of the post_id’s of every post in the topic. The front end provides access to specific post_numbers via the URL, but when such a URL is actually accessed the request made to the back end is in terms of post_ids (presumably accessed from the above mentioned array).
This is all well and good, but it seems like everything post_number is used for could be accomplished with post_id instead: post_id’s are always increasing, so they can be used to determine the relative ordering of posts in a topic. Since they are globally unique they are certainly unique within each topic, and so could be used in a reply_to_post_id that serves the same purpose as reply_to_post_number.
TLDR; What purpose does post_number serve that could not be easily accomplished with post_id? If there is none then removing it would streamline the data model, which would seem to be a good thing.