3 ms·

> Why can I not put an abstraction layer that provides me with the illusion of exactly-once delivery? You can do that. You can implement a video conferencing s

> Why can I not put an abstraction layer that provides me with the illusion of exactly-once delivery? You can do that. You can implement a video conferencing system ontop of TCP, and it will even work, technically. It will just have terrible performance characteristics that you'll never be able to fix. You might even call it fundamentally broken.

lisper 2y ago
OK, I don't dispute that, but that is a very different claim than "you can't get exactly-once delivery." You can (if you have at-least-once delivery).
- sethammons 2y ago
  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.
  - lisper 2y ago
    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?

lisper 2y ago

OK, I don't dispute that, but that is a very different claim than "you can't get exactly-once delivery." You can (if you have at-least-once delivery).

sethammons 2y ago
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.
- lisper 2y ago
  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?