Google Spanner: First Globally Scalable Database With External Consistency

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Google Spanner: First Globally Scalable Database With External Consistency

Posted by Unknown on Tuesday September 18, 2012 @12:04AM from the all-while-ironing-your-clothes dept.

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.

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This is a great step for people who need it by Chrisq · 2012-09-18 00:13 · Score: 5, Interesting

Though not many people will need huge multi-centre databases it has cracked some of the big problems. Interestingly some of these don't appear to affect google's main business.

Spanner has two features that are difcult to implement in a distributed database: it provides externally consistent reads and writes, and globally-consistent reads across the database at a timestamp.
One of the issues with large distributed data systems was that reads at different nodes could retrieve data at a different (though consistent) state. I have seen this on google, a search shows a recent news item, then another doesn't show it again, before it finally covers all nodes and is generally available.
More to it than NTP... by vlm · 2012-09-18 00:13 · Score: 3, Insightful

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.

--
"Science flies us to the moon. Religion flies us into buildings." - Victor Stenger
1. Re:More to it than NTP... by glop · 2012-09-18 02:10 · Score: 4, Informative
  
  GPS/Atomic clock is better than NTP. It's a system to distribute time that will have a 400ns precision (probably a couple microseconds once you reach the actual servers in the data center).
  If you use NTP or message passing you can't synchronize data centers more accurately than a couple milliseconds (assuming you have paths that are quite stable between them as transit time can be corrected).
  So basically GPS/Atomic clock lets you synchronize 2 systems that are far apart more precisely and without having to make them communicate.
  Note that Atomic clocks protect them from GPS outages, so they can really rely on the timestamps.
Re:Sounds really great by javilon · 2012-09-18 00:25 · Score: 2

They don't tell you where to get it. And no source available from the website. Before they go into oracle territory they need a product and a price tag.

--

When his defense asked, "Which computer has Jon Johansen trespassed upon?" the answer was: "His own."
Re:Protect data from governments? by rhsanborn · 2012-09-18 00:39 · Score: 2

Sure, just ask Julian Assange, or Kim Dot Com.

And hopefully you have no assets or presence in the US. Because while they may not be able to easily get the data in the Grand Caymans, they'll be able to make the rest of your life hell.
Re:GPS tampering by jiriw · 2012-09-18 01:11 · Score: 2

They will use WiFi triangulation to be location aware instead? :P
It seems it's the GPS clock signals they want to use here. When those are dropped I guess they'll fall back on their own atomic clocks. It might be a little less accurate 'though.
From T*A:

Google’s cluster-management software provides an implementation of the TrueTime API. This implementation keeps uncertainty small (generally less than 10ms) by using multiple modern clock references (GPS and atomic clocks).
Nothing in there about GPS being essential. Just needs 'multiple modern clock references'.
Re:GPS tampering by Anonymous Coward · 2012-09-18 01:41 · Score: 2, Informative

Then you'll be too worried about aeroplanes falling from the sky and ships running aground to be worried about database consistency, I guess.
Re:Sounds really great by Nerdfest · 2012-09-18 02:42 · Score: 2

They also give away the source on occasion ...