mysql - PHP forums - how to cope with unread discussions / topics / posts

There isn't a lot of choices.

1. mark every reader thread by each user.

   • Disadvantages: a lot of rows in very active forums
   • Advantages: Every user knows with post has read or not.

2. mark every unread thread by each user.
   

   • Disadvantages: a lot of space with "unreaded" rows if there is inactivity of a lot of users
   • Solutions: add a lifetime timestamp and delete old records with a cron
   • Advantages: Every user knows with post has read or not.

3. use timestamps to determine if show it as unread or not.

   • Disadvantages: The users don't know with are the real unread threads, the marks only show the "new trheads" since the last login
   • Advantage: Save space

The other alternative is mixing solutions, that is,

1 and 3) show thread as "unread" if they aren't older than X days and there isn't a row marked as readed for the user. The "read" rows can be deleted when they are X day older without affect anything.

Advantages

• less spaced used to determine unread threads

Disadvantages

• create a cron that keeps the system clean
• Users don't know if they read threads olders than x days.

Advantages

• Every user knows which "new posts" has read or not.