Spanner is Google's globally distributed relational database management system (RDBMS), the successor to BigTable. Google claims it is not a pure relational system because each table must have a primary key.
The Google F1 SQL database management system (DBMS) is built on it, and replaces Google’s custom MySQL.
Inside Google Spanner, the Largest Single Database on Earth
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http://www.zdnet.com/google-reveals-spanner-the-database-tech-that-can-span-the-planet-7000004421/