Deleting a thread or post is very slow

If I edit an EasyDiscuss post, the "save" process is quick. However, if I delete a post or thread it takes a long time (can be a minute or more and we have a pretty good server) and I can see that MySQL is running up the CPU and memory usage which slows the rest of the site down.

I'm guessing that this is due to one or more columns in the delete queries are not indexed (but I've also read that too much indexing can also slow down a larger site).

Either way, could you advise which fields/columns in which tables need to be set to be indexed for deletions?

Thanks. -- Rik