5 subtle ways you’re using MySQL as a queue, and why it’ll bite you
I've been met with looks of disgust for using a filesystem  to implement a queue, but I feel it's unjustified.  A modern unix filesystem is surprisingly well suited to this task: You get atomicity "for free", inotify allows it to be interrupt driven rather than polled, it inherently supports multiple processes (thus different parts of the system can be implemented in different languages), there's no need for locking as long as you implement the queue using directories and 'mv', and it's extremely quick to implement, understand, and modify.The only caveats are that of performance (with a traditional server I wouldn't worry about performance until you need to process hundreds of items per second, but on EC2 nodes that threshold is more near the range of dozens per second), and the need to regularly archive the "done" directory (cron solves this nicely).