Since this has come up a few times already: ab -c 5 -n 10 http://127.0.0.1:3000/widgets/http

That's not a benchmark, it's a proof of concept: http://github.com/igrigorik/async-rails/blob/master/app/cont...

/widgets/http makes an http request to /widgets, which does a 1s sleep query inside of mysql. All of this is happening on the same reactor loop, and finishes with ~2s, aka, the sleeps are not blocking the reactor and hence the "async stack".