SQS Non-Unique Message Delivery

One of the "gotchas" I wasn't aware of when I started developing with Amazons (very nice) SQS service is that they do not guarantee that message delivery is unique. ie. you may get the same message delivered multiple times.

This is a trade-off they've made with regards having less synchronization between message servers to provide more performance.

So when you're writing message consumers you need to make sure that they can handle processing the same message many times.