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> For the statement to hold true, AP systems would have to fail just as often as CP systems.

I think all that would need to be true is that there exists one CP system that has uptime figures comparable to AP systems. Then you could say that targeting AP is pointless, when you could either just use that system; or engineer your own new CP system to do the same things to achieve uptime as that system.




You can achieve high uptime in a CP system by assuring P will never happen, ending up with some kind of an AC system, but in practice it may be very costly, hard to setup and operate.

Can you imagine every ATM having a redundant networking connectivity and two independent power lines?

There is no free lunch. Comparing just availability figures is therefore not enough. Still an AP system may be preferable if it has the same availability at a fraction of a cost of that unicorn available and consistent system.


Note that a "CP system with high uptime" isn't suddenly an AC system. It still doesn't attempt to have 100% uptime, and its ecosystem of clients still must be built around the idea that the server can go down, if just for a few minutes a year.

This is different from an AP system, because an AP system has to be built from the ground up to assume that stupid corruptions will happen during netsplits and that it'll have to re-integrate them; while the CP system can just assume it'll all go down, and not have to have any of that extra code or infrastructure.

A good example of a high-uptime CP system that I'm aware of, is telecom switches. They're usually architected as simple pairs: one live, and one hot standby. And—even in platforms that don't have "hot upgrade" functionality—you can still upgrade both nodes without downtime by just intentionally causing connections to fail-over back and forth between the nodes.

Telecom switches have very little downtime. But they do go down, rather than becoming inconsistent. And the resulting architecture is much cheaper (in both hardware/networking costs, ops costs, and software development/maintenance costs) than the equivalent architecture you'd need to serve calls under AP guarantees.




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