Google Spanner: First Globally Scalable Database With External Consistency

vu1986 writes with this bit from GigaOm: "Google has made public the details of its Spanner database technology, which allows a database to store data across multiple data centers, millions of machines and trillions of rows. But it's not just larger than the average database, Spanner also allows applications that use the database to dictate where specific data is stored so as to reduce latency when retrieving it. Making this whole concept work is what Google calls its True Time API, which combines an atomic clock and a GPS clock to timestamp data so it can then be synched across as many data centers and machines as needed." Original paper. The article focuses a lot of the Time API, but external consistency on a global scale seems to be the big deal here. From the paper: "Even though many projects happily use Bigtable, we have also consistently received complaints from users that Bigtable can be difficult to use for some kinds of applications: those that have complex, evolving schemas, or those that want strong consistency in the presence of wide-area replication. ... Many applications at Google have chosen to use Megastore (PDF) because of its semi-relational data model and support for synchronous replication, despite its relatively poor write throughput. As a consequence, Spanner has evolved from a Bigtable-like versioned key-value store into a temporal multi-version database. Data is stored in schematized semi-relational tables; data is versioned, and each version is automatically timestamped with its commit time; old versions of data are subject to configurable garbage-collection policies; and applications can read data at old timestamps. Spanner supports general-purpose transactions, and provides a SQL-based query language." Update: 09/20 17:57 GMT by T : Also in a story at Slash BI.

More to it than NTP...

[vlm]

Making this whole concept work is what Google calls its True Time API, which combines an atomic clock and a GPS clock to timestamp data so it can then be synched across as many data centers and machines as needed.

I'm guessing there's a little more to it than reinventing and installing ntp on your DBMS server. That little bit more is the actual interesting part.