[Andreas]

If I add a new forum later do I have to rerun the query?

No. You will just have to set the amount of days in forum manager.

ill this ignore sticky topics? If I have something as a sticky I'd like it to be exempt from any/all pruning functions including this auto-prune.

No, it will also delete sticky threads. But this can be modified easily:

Replace

PHP Code:

$threads = $DB_site->query("SELECT threadid FROM " . TABLE_PREFIX . "thread WHERE forumid=$forum[forumid] AND lastpost <= " . (TIMENOW - ($forum['pruneafter'] * 86400))); 


With

PHP Code:

$threads = $DB_site->query("SELECT threadid FROM " . TABLE_PREFIX . "thread WHERE forumid=$forum[forumid] AND sticky != 1 AND lastpost <= " . (TIMENOW - ($forum['pruneafter'] * 86400))); 


Then it should ingore sticky threads.