message queueing vs background processing
Just read about this article:
http://www.mikeperham.com/2011/05/04/background-processing-vs-message-queueing/
One important viewpoint in this artile is: message queueing is a superset of background processing
girl_friday plugin is a backgroud processing gem, that no need install any MQ system. So for system don't need to queue up request, can use this instead of complicated MQ system.