For a personal project, I need to build a forum using PHP and MySQL. It is not possible for me to use an already-built forum package (such as phpBB).

I’m currently working through the logic needed to build such an application, but it’s been a long day and I’m struggling with the concept of handling unread posts for users. One solution I had was to have a separate table which essentially holds all post IDs and user IDs, to determine if they’ve been read:

tbl_userReadPosts: user_id, post_id, read_timestamp

Obviously, if a user’s ID appears in this table, we know they’ve read the post. This is great, except if we have thousdands of posts per day (which is more than possible in the system which is being proposed), and thousdands of users. This table would become huge within a matter of days, if not hours.

Another option would be to track the user’s last activity as a timestamp, and then retrieve all posts made after their last activity was updated. This works in theory, but let’s say a user is writing an extremely long post, and in the meantime several members also start new threads or reply to posts in other threads. When the user submits his new post, his last activity would be updated, and thus not match those made in the meantime.

Does anyone have experience with this, and how did you tackle it?

I’ve checked in phpBB and it seems that the system assigns a custom session to each user, and works on that basis, but the documentation is pretty sparse as to how this deals with unread posts.

Thoughts and opinions gratefully received, as always.