One of my recently deployed Rails app uses memcache with Phusion Passenger. I read on the Phusion documentation about the possibility of corrupted commands issued to memcache through the spawned processes within Passenger.

I added the declarations below within the config/environment.rb file to overcome this issue:

      begin
         PhusionPassenger.on_event(:starting_worker_process) do |forked|
             if forked
               # We're in smart spawning mode, so...
               # Close duplicated memcached connections - they will open themselves
                 CACHE.reset
             end
         end
     # In case you're not running under Passenger (i.e. devmode with mongrel)
     rescue NameError => error
   end
 

The CACHE constant is set within the cache_fu plugin. All the declaration does is similar to that outlined in the Appendix of the Phusion documentation with the addition of the ‘begin..rescue’ block to counteract exceptions which may arise.

I understand from comments on the Passenger google group that cache_fu causes problems with memcached. If anyone has any further information on the above please feel free to comment.