Cloud Spanner is the first and only relational database service that is both strongly consistent and horizontally scalable. With Cloud Spanner you enjoy all the traditional benefits of a relational database: ACID transactions, relational schemas (and schema changes without downtime), SQL queries, high performance, and high availability. But unlike any other relational database service, Cloud Spanner scales horizontally, to hundreds or thousands of servers, so it can handle the highest of transactional workloads. With automatic scaling, synchronous data replication, and node redundancy, Cloud Spanner delivers up to 99.999% (five 9s) of availability for your mission critical applications. In fact, Google’s internal Spanner service has been handling millions of queries per second from many Google services for years.

via Cloud Spanner | Automatic Sharding with Transactional Consistency at Scale  |  Google Cloud Platform