Google Research published at SIGMOD, 2012 and then published a paper about it at VLDB, 2013. Google used to use Sharded MySQL for their Ads system. But it had bad performance on availability, scalability and functionality. So Google decided to build a new database on Spanner to keep all RDBMS features but with scalability.
http://dl.acm.org/citation.cfm?id=2213954
Google Inc