See Introducing Cloud Spanner: a global database service for mission-critical applications and Inside Cloud Spanner and the CAP Theorem (Google Cloud Platform Blog) for details
"Google today announced the beta launch of Cloud Spanner, a new globally distributed database service for mission-critical applications. Cloud Spanner joins Google’s other cloud-based database services, like Bigtable, Cloud SQL and the Cloud Datastore, but with the crucial difference of offering developers the best of both traditional relational databases and NoSQL databases — that is, transactional consistency with easy scalability. Maybe the easiest way to think about Cloud Spanner is as an alternative for developers who are hitting the limits of traditional relational databases like MySQL or PostgreSQL.Google launches Cloud Spanner, its new globally distributed relational database service | TechCrunch
If the name Cloud Spanner sounds familiar, that’s probably because Google has long used a version of this database internally, and published a paper about it in 2012. As Google’s Deepti Srivastava told me, Google started working on Spanner in 2007 because it was looking for an alternative to MySQL, which previously ran many of the company’s products. Today, products like Google Photos and many of Google’s mission-critical applications run on Spanner. With Cloud Spanner, Google is making this same database service available to outside developers, as well."