It’s actually pretty simple: in phpbb_topics, there’s a field called “topic_moved_id”. When you move a topic and specify that a shadow topic be created, a new topic is added to the database. This topic then owns all the posts associated with the old topic, which becomes the “shadow topic”. The “topic_moved_id” field exists simply to let phpBB know the association between the topic and its shadow.

To remove the fields, all you have to is delete any topic_id that has a non-null topic_moved_id field. Now, the easiest way to do this would be DELETE FROM phpbb_topics WHERE topic_moved_id > 0;, but that deletes all the shadow topics. That’s decidedly not cool; I decided to leave the last 7-ish days of shadow topics.

So, I pulled up my handy-dandy UNIX timestamp converter, fed in 04 17 2005 00 00 00, and got 1113696000 as a timestamp. Working from there, the SQL query gets only marginally harder: DELETE FROM phpbb_topics WHERE topic_moved_id > 0 AND topic_time < 1113696000;. I executed that, and 748 shadow topics were gone from The Rumor Forum.

To turn this into a worthwhile phpBB modification, I just need to mimic how to put this in the Administration Panel in 2.0.x. I've got a couple modifications already installed that I can mimic, but for now, it's worth just posting this go-by for anyone else to use.

I have some ideas for extending this a bit, but other projects are clamoring for attention.