config.action_controller.asset_host = "assets%d.example.com"
Browsers typically open at most two simultaneous connections to a single host, which means your assets often have to wait for other assets to finish downloading. You can alleviate this by using a
%d wildcard in the
asset_host. For example, “assets%d.example.com”. If that wildcard is present Rails distributes asset requests among the corresponding four hosts “assets0.example.com”, …, “assets3.example.com”. With this trick browsers will open eight simultaneous connections rather than two.
image_tag("rails.png") # => <img alt="Rails" src="http://assets0.example.com/assets/rails.png" /> stylesheet_link_tag("application") # => <link href="http://assets2.example.com/assets/application.css" media="screen" rel="stylesheet" />