I don't have a stake in the Ruby webserver wars, but the unicorn site has a very good discussion about how it works internally, why it's build as it is, pros & cons etc..

This seems to be missing from most of these project sites, which are often just marketing (look! It's better!!), and therefore not very trustworthy.

From the outside it looks like the biggest differentiator in each generation of ruby servers (and, I guess, db managment systems :) is not that the new is better or worse, but simply that has different trade-offs.

I did some performance analysis on puma vs unicorn vs thin a while ago:

http://ylan.segal-family.com/blog/2012/08/20/better-performa...

Although as noted in the comments, I neglected to run threadsafe! and should have probably tried rubinius or jruby. I have been meaning to redo. Take with a grain of salt

You should give a try to puma 2.0 currently in beta 6 (https://rubygems.org/gems/puma). Lots of performance improvements. I haven't benchmarked it but my guess is it outperforms unicorn.

You seem have written one of the very few articles I've seen benchmarking this. I'd love to know more about how Puma compares to Unicorn (especially unicorn configurations mentioned by some in this conversation) and Thin for serving rails on Heroku. Many of the Unicorners pushing their solution don't appear to be aware of Puma and its potential benefits. I'm curious if Puma with MRI has benefits, too. Thanks!

AFAIK Puma should have a lower memory footprint on MRI than Thin but I haven't done benchmarks myself.

Also note that Rails 4 will have threadsafe! on by default, too, so if you didn't have it on here, that'll make it different for those apps.

I have been using it on a few small projects. Haven't ran into an issue yet and the setup has been really easy.

We are running a smaller app on JRuby using Puma with thread safe on. It has a significantly smaller footprint, as we are only booting one server.

Overall really solid, though more useful if you can use something other than MRI.