February 17th, 2008 A 'problem' with the Mongrel/Rails platform A request comes in to the web server, and if it's dynamic, falls down to a waiting mongrel process. Mongrel calls Rails which wraps a big lock around most of the request/response cycle so the mongrel thats serving the request has to wait for a response from Rails to unlock and start serving other requests. This is the Blocked Thread stability anti-pattern that Michael Nygard talks about in Release It!. The problem is that Nginx or Apache doesn't know that a mongrel is blocked and keeps blindly sending requests. Thats means that even a single blocked mongrel will result in some slow responses for requests that come in to that same mongrel. Cut the Request Fat And one way to do that is to use the "Skinny Request, Fat Backend" principle. What that means in practical terms is pretty simple: Do as little as possible inside of the Request/Response cycle.