
Google Spans Planet with GPS-Powered Database (2012) - sds111
https://www.wired.com/2012/09/google-spanner/
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ars
This article explains exactly nothing.

You can replace the word TrueTime, with "Magic" and learn exactly as much.

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sumitgt
The recent paper on Spanner has some details of how it is used if you are
interested.

[https://static.googleusercontent.com/media/research.google.c...](https://static.googleusercontent.com/media/research.google.com/en//archive/spanner-
osdi2012.pdf)

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erentz
Should have a 2012 in it. Can someone clarify something for me. The GPS part
gets talked about a lot in these articles, but it's never been clear why. Does
Google go as far as putting a GPS receiver in _every_ server? If not, what is
so special about this? (People have been using GPS as a time source on
networks for decades. But the way articles talk about it, this is super-duper
novel.)

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packetslave
Take a look at Spanner paper for details. There’s a set of time master
machines per datacenter that have GPS receivers attached, and a set of
“Armageddon masters” that have atomic clocks attached. Regular machines
(including the Spanner servers) run a time slave daemon that talks to the
master machines.

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sleavey
Naively I'd assume that the improvement in time accuracy GPS clocks provide
must be greater than the harmful effect on accuracy created by network
latency, even within data centres: you can't _guarantee_ that a packet will
arrive on time, since switches can, I believe as part of their protocol, apply
a random wait to a packet. I assume there must be some special method to
maintain a synchronous connection to the clock on each server over the
network. Could it be as simple as some QoS rules in the switches for NTP
packets?

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itronitron
you can make one of these yourself now if you need highly accurate (but not
completely accurate all the time) time stamps...
[https://learn.adafruit.com/arduino-
clock/overview](https://learn.adafruit.com/arduino-clock/overview)

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mehrdada
(2012)

