Lobsters sysop here - we're having trouble keeping up with YC News's level of traffic. We're not going to crash, but the unicorn worker pool is small enough that lots of users are getting 500s. I'm adding some caching.
SQL isn't a good match for the recursive structure of comments (and our version of mariadb from LTS Ubuntu doesn't support recursive common table expressions), so the app pulls all comments in ActiveRecord objects and threads/sorts them there. It's expensive and uncached. Codebase is here if you're curious: https://github.com/lobsters/lobsters
Traffic counting has to wait until I have spare attention, which is also a shallow resource pool. :)