Review: Google Cloud Spanner takes SQL to NoSQL scaleOn July 24, 2017 by Zander
Scaling a relational database isn’t easy. Scaling a relational database out to multiple replicas and regions over a network while maintaining strong consistency, without sacrificing performance, is really hard.
How hard? The CAP Theorem says that you can only have two of the following three properties: consistency, 100 percent availability, and tolerance to network partitions.