I recently switch from a mod_proxy / thin setup to Phusion Passenger and my application started to do the funniest things and the production.log was full with errors related to memcached.
It seems, that passengers spawn method “smart” isn’t compatible with memcached. Within seconds on a lightly loaded server the cache gets corrupted big time.
I got better results with a newer memcache client (the ruby gem actually), but for that i need to remove the client from the rails vendor lib. Furthermore, under higher load there still where errors.
Only solution is to set the spawn method to conservative like so
Problem seems to be known in the Phusion and Rails teams.