I was looking at my slow query log and found several queries similiar to this one:
I had to cut out the postids because the query was over 350,000 characters and too large to post here.
Code:
# Query_time: 16 Lock_time: 0 Rows_sent: 43736 Rows_examined: 87970
SELECT thread.threadid, thread.forumid, post.userid
FROM thread AS thread INNER JOIN post AS post ON(thread.threadid = post.threadid )
WHERE post.postid IN (MANY POST IDS) AND post.visible = 1;