To wit: In terms of CAP, Spanner claims to be both consistent and highly available despite operating over a wide area, which many find surprising or even unlik

To wit: In terms of CAP, Spanner claims to be both consistent and highly available despite operating over a wide area, which many find surprising or even unlikely. The claim thus merits some discussion. 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. However, no system provides 100% availability, so the pragmatic question is whether or not Spanner delivers availability that is so high that most users don't worry about its outages. For example, given there are many sources of outages for an application, if Spanner is an insignificant contributor to its downtime, then users are correct to not worry about it. https://cloudplatform.googleblog.com/2017/02/inside-Cloud-Spanner-and-the-CAP-Theorem.html https://cloudplatform.googleblog.com/2017/02/inside-Cloud-Sp... (written by Eric Brewer, who proposed CAP)