[bboreham]

I'm not involved in the project, but you do this if you want the same robustness as an rdbms, e.g. if a client gets an acknowledgement back from the queue then the data is definitely captured and won't be lost if the queue process then crashes.

[elvinyung]

I agree that it makes sense in certain circumstances and definitely depends on requirements (not only transactional enqueues which you mentioned, but also a lot of times it's a need for O(lg n) lookup/update/deletion of jobs in flight), and I've also seen a few MySQL-backed queues in production that can handle fairly high throughputs. I'm particularly and mostly interested why this project does it.