Alyce brought up this issue in the "pet peeves" topic and I think it needs more in-depth discussion.

Alyce wrote:

I like an easy way to view recent posts. The LB board does not give you the ability to display only unread posts, or more than 10 recent posts.

Conforums (and other sites that use the same software) store which topics have unread posts in their database. I presume that the table gets updated when the user logs on because it would become very burdensome to do this for all users every time someone creates or deletes a post. This data by itself probably takes up several megabytes (if not GB) due to the number of accounts. If they tried to track the read status of individual posts, I'm sure that would consume at least 10 times the storage.

Besides, it wouldn't be practical to store the status of individual posts because they almost always appear in multiples. But if it could display all of the unread posts, how would the software know if you actually read them?

At the other extreme is software like phpBB, which doesn't store any read status data. Instead, it determines what is "new" based solely on when a user last visited compared to when posts were created. If the topics are not read then, upon the next visit those same posts are considered "old."

There might be some middle ground, but it could be complicated. It would involve a database table, but with limits. There might be three levels: admins, mods, and regular users.

Admins might have unlimited status. Mods might be unlimited for the area they moderate, but are otherwise regular users. Everyone else might be limited to 20 topics per forum, or whatever the admins choose.

Can anyone see a better way?

I don't care about read/unread so much. Proboards allows the admin to determine the number of "most recent posts" that show in the info box at the bottom of the forum. Conforums has only the standard 10. A "xxx most recent posts" wouldn't need to be stored in a database, correct? Only the xxx would need to be stored.

Posts since last visit is not hard to do, it only takes one additional info about the member.

Unread posts needs an additional index for every thread, which contains the members who haven't read the topic since the last reply.
This would be a huge amount and would need a purge for members, which have left but did not delete their account or are only visiting once in a while.

A member selectable value of recent posts in conjunction with posts since last visit could be an option.
I would allow the most recent post count to be set in the members profile, selecting from 10, 20, 50, 100.
The search would find the posts since last visit up to the count specified.
This should reduce database workload too.

The problem with the "X most recent posts" feature is the loss of context and continuity. I'm considering how feasible it is to do this but group the posts by topic.

So it seems to be better to have "X most recent threads", which should be a smaller number anyway.

Store a timestamp of the user's last visit. Each message has a posted timestamp. Whenever a message is posted, each board's last updated timestamp is updated too.

For the main page, you only have to show which forums have unread messages. You're already querying the boards table anyway, so just get the last updated timestamp and compare to the user's last visit timestamp. When you visit a particular board, the method is similar, but with individual threads instead of boards.

For unread since last visit, query for messages posted after the the user's last visit.

(This is a lot of what I've been playing with away from LB. Algorithms and theory doesn't come up much.)