I just switched CityDiff to Unicorn on Heroku. The site is using a single free dyno that was originally running Thin.
After the switch to Unicorn, I'm seeing faster response times for AJAX requests and less overall memory usage.
Here is my configuration.
web: bundle exec unicorn -p $PORT -c ./config/unicorn.rb
before_fork do |server, worker|
Rails.logger.info('Disconnected from ActiveRecord')
after_fork do |server, worker|
Rails.logger.info('Connected to ActiveRecord')
Thanks to railsonfire for the inspiration. http://blog.railsonfire.com/2012/05/06/Unicorn-on-Heroku.html