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Comment by Chickenosaurus | Hacker News Reader

According to a paper by Eric Brewer, the author of the original CAP theorem, Google Spanner technically is not a CA system [1]. It is advertised as such because partitons are supposed to be exceedingly rare as the infrastructure is outstanding and a lot of operating experience is present [1].

I believe at the end of the day the CAP theorem is too fuzzy for such discussions.

[1] https://research.google.com/pubs/pub45855.html

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Theorems are all well and good, but ultimately the thing that matters is the experience of using the system "IRL" as the kids say. If spanner is up 99.99% of the time, and is consistent at all times, it is probably not going to be the weak link in your software chain.

(Fwiw their slo for multi-regional instances is 99.999%, although I have no idea what their measured performance is against that objective.)

The paper says:

"Does this mean that Spanner is a CA system as defined by CAP? The short answer is “no” technically, but “yes” in effect and its users can and do assume CA.

The purist answer is “no” because partitions can happen and in fact have happened at Google, and during (some) partitions, Spanner chooses C and forfeits A. It is technically a CP system."

which I believe is another way to word what I say in my post above.

I agree. I did not mean to refute your point, but to provide more context.

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