I'm trying to switch the session store in Rails 3 by changing the
config/application.rb as following:

config/application.rb

-----------------------------------

memcache_options = {
  :compression => true, 
  :debug => false, 
  :namespace => "xx-cache", 
  :readonly => false, 
  :urlencode => false 
} 
CACHE = MemCache.new(memcache_options) 
CACHE.servers = ['127.0.0.1:17898'] 

#check if CACHE is connected and can get value out 
#puts CACHE.get('key') 

config.action_dispatch.session = { 
  :key => '_xx_session', 
  :secret => 'xx', 
  :cache => CACHE, 
  :expires => 900 
} 
config.action_dispatch.session_store = :mem_cache_store

-----------------------------------

Memcache server is running. However, when run "rails s", i got this
message:
=> Booting WEBrick => Rails 3.0.0.beta3 application starting in development on http://0.0.0.0:3000 => Call with -d to detach => Ctrl-C to shutdown server Exiting
/usr/lib/ruby/gems/1.9.1/gems/actionpack-3.0.0.beta3/lib/ action_dispatch/middleware/session/mem_cache_store.rb:19:in
initialize': #<ActionDispatch::Session::MemCacheStore:0xa302950> unable to find server during initialization. (RuntimeError)

It seems the session option :cache was not passed correctly.