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Comment by sulam | Hacker News Reader

Not "close" to impossible -- actually impossible.

Also known as the Two Generals Problem

The reasons this is "currently" impossible are: - We cannot build communication infrastructures that are 100% reliable - We build apps that actually crash.

I would not venture as far as to say this is impossible. If one day we are able to leverage quantum entanglement phenomenon in telecommunications network this would certainly be very much possible.

The machine that reads the quantum entagled particles will still occasionally break or have coding errors.

I don't really know a thing about that sort of network, but if you can assume a reliable network, the machine reading the packets going down shouldn't matter. The sender won't get an "ACK", will know the other machine is at fault and not the network, and can resend.

Given a "perfect network" I think exactly-once-delivery is possible, right?

What if the sender fails before it can fully process the ACK? When it comes online again it won't know that the last message sent was delivered.

Transactions.

You've been downvoted, but the trick would be to convert asynchronous messaging to synchronous processing that proceeds at a predictable tick. That would make it possible to bypass the FLP result. I'm willing to imagine quantum entanglement could pull this off if we were able to entangle actual transistors. Dunno how plausible that is, but points for creativity if nothing else.

> We build apps that actually crash.

And disks that fail and memory that bitflips and communication methods that are susceptible to random noise and machines dependent on failable power sources.

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