5 ms·

This is basically impossible: for strong consistency, you need very accurate clocks. Google installs GPS clocks in its data centers. Also Bigtable, Spanners pr

This is basically impossible: for strong consistency, you need very accurate clocks. Google installs GPS clocks in its data centers. Also Bigtable, Spanners predecessor, is not open source too.

cormacrelf 9y ago
Well, that's how Spanner's consistency works. CockroachDB uses a hybrid vclock/wall clock solution that's possibly going to be tuneable to just clocks. https://jepsen.io/analyses/cockroachdb-beta-20160829 https://jepsen.io/analyses/cockroachdb-beta-20160829
atemerev 9y ago
Every GPS chip in every GPS-enabled device includes the clock — by design, it can't work without it. So perhaps it is possible to quickly hack something from a cheap Android phone placed somewhere near the window?
- nickpsecurity 9y ago
  That was sams idea I had. I found that SparkFun even had a guide on it: https://www.sparkfun.com/pages/GPS_Guide https://www.sparkfun.com/pages/GPS_Guide
  - detaro 9y ago
    Better resources: http://www.satsignal.eu/ntp/Raspberry-Pi-NTP.html http://www.satsignal.eu/ntp/Raspberry-Pi-NTP.html https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts (I don't understand a lot discussed there, but many interesting links and info about current deals to be found) There also are differences between the quality of the timing output of different GPS modules, with some being optimized for timing applications (as opposed to location finding)
    - nickpsecurity 9y ago
      Appreciate it as I am wanting timing-focused ones.
- timelol 9y ago
  Using GPS as your time source is a fabulously good way to trash your entire database during a leap second. See this paper for a discussion on how essentially everybody but Google gets this wrong: http://crin.eng.uts.edu.au/~darryl/Publications/LeapSecond_camera.pdf http://crin.eng.uts.edu.au/~darryl/Publications/LeapSecond_c...
  - mastax 9y ago
    GPS time does not have leap seconds: http://www.oc.nps.edu/oc2902w/gps/timsys.html http://www.oc.nps.edu/oc2902w/gps/timsys.html > GPS Time is a uniformly counting time scale ... The word "uniformly" is used above to indicate that there are no "leap seconds" in this time system. > The GPS message contains information that allows a receiver to convert GPS Time into Universal Time In fact the article you linked corroborates this, because they used GPS time to show how inaccurate NTP servers are.

This is basically impossible: for strong consistency, you need very accurate clocks. Google installs GPS clocks in its data centers. Also Bigtable, Spanners predecessor, is not open source too.

cormacrelf 9y ago

Well, that's how Spanner's consistency works. CockroachDB uses a hybrid vclock/wall clock solution that's possibly going to be tuneable to just clocks. https://jepsen.io/analyses/cockroachdb-beta-20160829 https://jepsen.io/analyses/cockroachdb-beta-20160829

atemerev 9y ago

Every GPS chip in every GPS-enabled device includes the clock — by design, it can't work without it. So perhaps it is possible to quickly hack something from a cheap Android phone placed somewhere near the window?

nickpsecurity 9y ago
That was sams idea I had. I found that SparkFun even had a guide on it: https://www.sparkfun.com/pages/GPS_Guide https://www.sparkfun.com/pages/GPS_Guide
- detaro 9y ago
  Better resources: http://www.satsignal.eu/ntp/Raspberry-Pi-NTP.html http://www.satsignal.eu/ntp/Raspberry-Pi-NTP.html https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts (I don't understand a lot discussed there, but many interesting links and info about current deals to be found) There also are differences between the quality of the timing output of different GPS modules, with some being optimized for timing applications (as opposed to location finding)
  - nickpsecurity 9y ago
    Appreciate it as I am wanting timing-focused ones.
timelol 9y ago
Using GPS as your time source is a fabulously good way to trash your entire database during a leap second. See this paper for a discussion on how essentially everybody but Google gets this wrong: http://crin.eng.uts.edu.au/~darryl/Publications/LeapSecond_camera.pdf http://crin.eng.uts.edu.au/~darryl/Publications/LeapSecond_c...
- mastax 9y ago
  GPS time does not have leap seconds: http://www.oc.nps.edu/oc2902w/gps/timsys.html http://www.oc.nps.edu/oc2902w/gps/timsys.html > GPS Time is a uniformly counting time scale ... The word "uniformly" is used above to indicate that there are no "leap seconds" in this time system. > The GPS message contains information that allows a receiver to convert GPS Time into Universal Time In fact the article you linked corroborates this, because they used GPS time to show how inaccurate NTP servers are.