ruby 1.9.2 and other ruby implementations may not return the same has…

…h value for the same string each time. This can result in your static assets being served from different asset hosts, which makes browser caching less effective. Use md5 or some other digest method instead.

actionpack/lib/action_view/helpers/asset_tag_helper.rb

@@ -57,7 +57,7 @@ module Helpers #:nodoc:
     # +asset_host+ to a proc like this:
     #
     #   ActionController::Base.asset_host = Proc.new { |source|
-    #     "http://assets#{source.hash % 2 + 1}.example.com"
+    #     "http://assets#{Digest::MD5.hexdigest(source).to_i(16) % 2 + 1}.example.com"
     #   }
     #   image_tag("rails.png")
     #   # => <img alt="Rails" src="http://assets1.example.com/images/rails.png?1230601161" />