TrueTime API: How Google’s Servers Know What Time It Is
November 26th, 2012Via: Wired:
But with Spanner, Google discarded the NTP in favor of its own timing-keeping mechanism. It’s called the TrueTime API. “We wanted something that we were confident in,” Fikes says. “It’s a time reference that’s owned by Google.”
Rather than rely on outside clocks, Google equips its Spannerized data centers with its own atomic clocks and GPS (global positioning system) receivers, not unlike the one in your iPhone. Tapping into a network of satellites orbiting the Earth, a GPS receiver can pinpoint your location, but it can also tell time.
These time-keeping devices connect to a certain number of master servers, and the master servers shuttle time readings to other machines running across the Google network. Basically, each machine on the network runs a daemon — a background software process — that is constantly checking with masters in the same data center and in other Google data centers, trying to reach a consensus on what time it is. In this way, machines across the Google network can come pretty close to running a common clock.
