What is the most efficient way to create a forum lightbulb (unread) system?

[nowe]

Alright, another interesting problem over at Route 50.We wanted to implement a true forum lightbulb system where posts that are unread by a user (after the user's account is created) show as unread until that status is cleared or until the user reads them.We figured the best and easiest way to do this would be to implement a table of unread messages.The Columns are: \[code\]user_id\[/code\], \[code\]board_id\[/code\], \[code\]thread_id\[/code\], \[code\]post_id\[/code\], \[code\]timestamp\[/code\], and \[code\]hidden\[/code\]This is working very well and very quickly for seeing which boards/threads/posts are unread (and linking to them) per user, however it is INCREDIBLY slow for a user to post to the forum even though only a single SQL query is being run:\[code\]INSERT IGNORE INTO `forums_lightbulb` SELECT `id`,'x','x','x',UNIX_TIMESTAMP(),0 FROM `users`\[/code\]I'm sure this is the result of having 3065 user accounts. How can I speed up this process? I'd prefer to keep the system as Real-Time as possible.Important Note: Please limit your answers to a shared hosting environment with no additional budget. We are limited to PHP and MySQL 5.1.53-log