Comment by lisper
As you have described it, you are right, it's not. But presumably the thing discarding the duplicates then does something with the non-duplicates, like deliver then to something else. That is exactly-once delivery.
As you have described it, you are right, it's not. But presumably the thing discarding the duplicates then does something with the non-duplicates, like deliver then to something else. That is exactly-once delivery.
You wrote in the post:
>This post was intended to be about human communication more than distributed systems or network protocols
But resorting to technical minutiae as you have done doesn't seem germane to "human communication". Honestly, seeing such mental gymnastics just to avoid losing face on an internet argument is really disappointing.
To discard the duplicates, you need to update your state based on the first message and consult that state for all subsequent messages. Someone must be delivered those messages for this to happen.
If you say that someone can then pass you messages exactly once over a perfectly reliable channel, well.. sure. But the system still has to deal with duplicate delivery and update its state based on that. (And potentially must durably persist this state. And, then, if your application doesn't have exactly the same persistence/transactional boundaries as what's doing the deduping, you have problems...).