assets.cache_store now defaults to filesystem. You will want to share tmp/assets_cache between deploys.

actionpack/lib/sprockets/railtie.rb

@@ -63,8 +63,8 @@ module Sprockets
 
         env.logger = Rails.logger
 
-        if env.respond_to?(:cache)
-          env.cache = assets.cache_store || Rails.cache
+        if env.respond_to?(:cache) && assets.cache_store != false
+          env.cache = ActiveSupport::Cache.lookup_store(assets.cache_store) || Rails.cache
         end
 
         if assets.compress

railties/lib/rails/application/configuration.rb

@@ -30,6 +30,7 @@ module Rails
         @log_level                   = nil
         @middleware                  = app_middleware
         @generators                  = app_generators
+        @cache_store                 = [ :file_store, "#{root}/tmp/cache/" ]
 
         @assets = ActiveSupport::OrderedOptions.new
         @assets.enabled    = false
@@ -37,6 +38,7 @@ module Rails
         @assets.precompile = [ /\w+\.(?!js|css).+/, /application.(css|js)$/ ]
         @assets.prefix     = "/assets"
 
+        @assets.cache_store    = [ :file_store, "#{root}/tmp/assets_cache/" ]
         @assets.js_compressor  = nil
         @assets.css_compressor = nil
       end
@@ -70,7 +72,6 @@ module Rails
           paths.add "public/javascripts"
           paths.add "public/stylesheets"
           paths.add "tmp"
-          paths.add "tmp/cache"
           paths
         end
       end
@@ -95,16 +96,6 @@ module Rails
         YAML::load(ERB.new(IO.read(paths["config/database"].first)).result)
       end
 
-      def cache_store
-        @cache_store ||= begin
-          if File.exist?("#{root}/tmp/cache/")
-            [ :file_store, "#{root}/tmp/cache/" ]
-          else
-            :memory_store
-          end
-        end
-      end
-
       def log_level
         @log_level ||= Rails.env.production? ? :info : :debug
       end

railties/lib/rails/generators/rails/app/app_generator.rb

@@ -117,7 +117,8 @@ module Rails
     end
 
     def tmp
-      empty_directory_with_gitkeep "tmp/cache"
+      empty_directory "tmp/cache"
+      empty_directory "tmp/assets_cache"
     end
 
     def vendor

railties/lib/rails/tasks/tmp.rake

@@ -4,7 +4,7 @@ namespace :tmp do
 
   desc "Creates tmp directories for sessions, cache, sockets, and pids"
   task :create do
-    FileUtils.mkdir_p(%w( tmp/sessions tmp/cache tmp/sockets tmp/pids ))
+    FileUtils.mkdir_p(%w( tmp/sessions tmp/cache tmp/sockets tmp/pids tmp/assets_cache ))
   end
 
   namespace :sessions do
@@ -18,6 +18,7 @@ namespace :tmp do
     # desc "Clears all files and directories in tmp/cache"
     task :clear do
       FileUtils.rm_rf(Dir['tmp/cache/[^.]*'])
+      FileUtils.rm_rf(Dir['tmp/assets_cache/[^.]*'])
     end
   end
 

railties/test/application/paths_test.rb

@@ -48,7 +48,6 @@ module ApplicationTests
       assert_path @paths["vendor"],              "vendor"
       assert_path @paths["vendor/plugins"],      "vendor/plugins"
       assert_path @paths["tmp"],                 "tmp"
-      assert_path @paths["tmp/cache"],           "tmp/cache"
       assert_path @paths["config"],              "config"
       assert_path @paths["config/locales"],      "config/locales/en.yml"
       assert_path @paths["config/environment"],  "config/environment.rb"

railties/test/generators/app_generator_test.rb

@@ -34,6 +34,7 @@ DEFAULT_APP_FILES = %w(
   vendor
   vendor/assets
   vendor/plugins
+  tmp/assets_cache
   tmp/cache
 )