Remove these:
comment_thread_id_1
author_id_1
last_activity_at_-1
votes.down_1__type_1
votes.up_1__type_1
delete_spam_1
Modify these:
Add these:
db.contents.ensureIndex({"_type" : -1, "course_id" : 1, "pinned" : -1, "endorsed": -1, "last_activity_at" : -1, "created_at": -1}, {"background":true})
db.contents.ensureIndex({"_type" : -1, "course_id" : 1, "pinned" : -1, "endorsed": -1, "votes.point" : -1, "created_at": -1}, {"background":true})
db.contents.ensureIndex({"_type" : -1, "course_id" : 1, "pinned" : -1, "endorsed": -1, "comment_count" : -1, "created_at": -1}, {"background":true})