Read the two general's problem. It is proven that exactly once _delivery_ is a physical and mathematical impossibility.
Like you said, you can simulate it with exactly once _processing_. But to do that, you have to know to do that.
Others are saying "you can't divide by zero" and you are saying "yeah, but if I detect a zero and the do something different, then it is the same thing." No, knowing you have to do something is the very point of acknowledging you can't divide by zero.
Because you can't have exactly once delivery, you have to deal with it. One trick is duplicate checks or idempotent writes. This gives exactly once processing. This also takes additional overhead and why audio and video stream processing doesn't typically do the additional checks.
I have fixed many bugs written by people who believe the network is reliable. I even hired one when during the interview and we talked about this kind of issue that they realized why they were getting duplicated writes reading from sqs or sns at $existing_job. They were green but smart and she became a real asset to the team.
What makes you thin the 2GP is relevant here? 2GP has to do with coordination and consensus, not exactly-once-delivery.
> you can simulate it with exactly once _processing_
What exactly do you think is the difference between "simulating" exactly-once delivery and actually having exactly-once delivery? What do you think "delivery" means in the context of a computer network?
