Remove any indexes acorss 'updated_at' field that are no longer in use for unread_comment_count.
Test removal of indexes under a load test.
Do u think its time we remove this index?
Given your testing, it is probably fine, but it also doesn't hurt to have it in.
: Do you have any thoughts on whether we should wait for the Discussions kill switch before doing any index clean-up?
Yeah, if it's just a cleanup task, it can wait until we have an off switch.