"exactly once" is actually pretty common. You can read about how Google does it in their MillWheel paper: http://static.googleusercontent.com/media/research.goo

"exactly once" is actually pretty common. You can read about how Google does it in their MillWheel paper: http://static.googleusercontent.com/media/research.google.com/en//pubs/archive/41378.pdf http://static.googleusercontent.com/media/research.google.co... They also compare their guarantees to other streaming systems, and they're not the only one to offer exactly once.