Pinboard (jm)
https://pinboard.in/u:jm/public/
recent bookmarks from jmThe 26,000-Year Astronomical Monument Hidden in Plain Sight at the Hoover Dam2019-01-30T12:25:14+00:00
https://medium.com/the-long-now-foundation/the-26-000-year-astronomical-monument-hidden-in-plain-sight-9ec13c9d29b5
jmThe center of the circle traced by the axial precession is actually the massive flag pole in the center of the plaza. This axial circle is prominently marked around the pole, and the angle of Polaris was depicted as precisely as possible to show where it would have been on the date of the dam’s opening. Hansen used the rest of the plaza floor to show the location of the planets visible that evening, and many of the bright stars that appear in the night sky at that location.
By combining planet locations with the angle of precession, we are able to pinpoint the time of the dam’s completion down to within a day. We are now designing a similar system — though with moving parts — in the dials of the 10,000 Year Clock. It is likely that at least major portions of the Hoover Dam will still be in place hundreds of thousands of years from now. Hopefully the Clock will still be ticking and Hansen’s terrazzo floor will still be there, even if it continues to baffle visitors.
(Via Tony Finch)]]>hoover-dam history precession astronomy long-now polaris vega thuban stars clockshttps://pinboard.in/https://pinboard.in/u:jm/b:d006414f72bb/Leap Smear | Public NTP | Google Developers2017-01-04T23:14:54+00:00
https://developers.google.com/time/smear
jmgoogle clocks time ntp leap-smearing leap-second opshttps://pinboard.in/https://pinboard.in/u:jm/b:102ddfaef4da/Lamport timestamps2016-05-24T11:08:11+00:00
https://en.wikipedia.org/wiki/Lamport_timestamps
jmvector-clocks distributed programming algorithm clocks time leslie-lamport coding distcomphttps://pinboard.in/https://pinboard.in/u:jm/b:03f67ba15148/TIL: clock skew exists2016-02-10T15:48:45+00:00
http://jvns.ca/blog/2016/02/09/til-clock-skew-exists/
jmclocks clock-skew ntp realtime time bugs distcomp reliability skewhttps://pinboard.in/https://pinboard.in/u:jm/b:9eea6afc942d/Introducing: The World's First Fully Functional 3D Printed Watch: The Christoph Laimer Tourbillon2016-01-15T14:51:05+00:00
https://www.hodinkee.com/articles/a-major-step-forward-in-horological-additive-manufacturing-christoph-laimers-3d-printed-tourbillon
jmwatches 3d-printing clocks things via:bruceshttps://pinboard.in/https://pinboard.in/u:jm/b:f5139c8cb1c4/Hybrid Logical Clocks2015-06-04T10:56:21+00:00
http://muratbuffalo.blogspot.ie/2014/07/hybrid-logical-clocks.html
jmhlc clocks logical-clocks time synchronization ordering events logs papers algorithms truetime distcomphttps://pinboard.in/https://pinboard.in/u:jm/b:e803e9509d1c/Five different ways to handle leap seconds with NTP2015-06-02T13:55:04+00:00
http://developerblog.redhat.com/2015/06/01/five-different-ways-handle-leap-seconds-ntp/
jmWith ntpd, the kernel backward step is used by default. With ntpd versions before 4.2.6, or 4.2.6 and later patched for this bug, the -x option (added to /etc/sysconfig/ntpd) can be used to disable the kernel leap second correction and ignore the leap second as far as the local clock is concerned. The one-second error gained after the leap second will be measured and corrected later by slewing in normal operation using NTP servers which already corrected their local clocks.
It's all pretty messy though :(]]>ntpd ntp chronyd clocks time synchronization via:fanf linux leap-secondshttps://pinboard.in/https://pinboard.in/u:jm/b:52c79bcfcdf0/NTP's days are numbered for consumer devices2014-08-18T13:09:34+00:00
http://engineering.bergcloud.com/2014/08/problem-with-ntp/
jmUnfortunately for us, the traditional and most widespread method for clock synchronisation (NTP) has been caught up in a DDoS issue which has recently caused some ISPs to start blocking all NTP communication. [....] Because the DDoS attacks are so widespread, and the lack of obvious commercial pressure to fix the issue, it’s possible that the days of using NTP as a mechanism for setting clocks may well be numbered. Luckily for us there is a small but growing project that replaces it.
tlsdate was started by Jacob Appelbaum of the Tor project in 2012, making use of the SSL handshake in order to extract time from a remote server, and its usage is on the rise. [....] Since we started encountering these problems, we’ve incorporated tlsdate into an over-the-air update, and have successfully started using this in situations where NTP is blocked.
]]>tlsdate ntp clocks time sync iot via:gwire ddos isps internet protocols securityhttps://pinboard.in/https://pinboard.in/u:jm/b:a1ce1cd2ed6d/The trouble with timestamps2013-10-14T09:45:54+00:00
http://aphyr.com/posts/299-the-trouble-with-timestamps
jmTimestamps, as implemented in Riak, Cassandra, et al, are fundamentally unsafe ordering constructs. In order to guarantee consistency you, the user, must ensure locally monotonic and, to some extent, globally monotonic clocks. This is a hard problem, and NTP does not solve it for you. When wall clocks are not properly coupled to the operations in the system, causal constraints can be violated. To ensure safety properties hold all the time, rather than probabilistically, you need logical clocks.
]]>clocks time distributed databases distcomp ntp via:fanf aphyr vector-clocks last-write-wins lww cassandra riakhttps://pinboard.in/https://pinboard.in/u:jm/b:dcc3c0071909/modern JVM concurrency primitives are broken if the system clock steps backwards2013-09-05T13:49:34+00:00
http://bbossola.wordpress.com/2013/09/04/jvm-issue-concurrency-is-affected-by-changing-the-date-of-the-system/
jmclocks timing ntp slew sync step pthreads java jvm timers clock_realtime clock_monotonichttps://pinboard.in/https://pinboard.in/u:jm/b:f27e8c19cc8c/Low-latency stock trading "jumps the gun" due to default NTP configuration settings2013-06-05T20:40:42+00:00
http://www.nanex.net/aqck2/4306.html
jmOn June 3, 2013, trading in SPY exploded at 09:59:59.985, which is 15 milliseconds before the ISM's Manufacturing number released at 10:00:00. Activity in the eMini (traded in Chicago), exploded at 09:59:59.992, which is 8 milliseconds before the news release, but 7 milliseconds after SPY. Note how SPY and the eMini traded within a millisecond for the Consumer Confidence release last week, but the eMini lagged SPY by about 7 milliseconds for the ISM Manufacturing release. The simultaneous trading on Consumer Confidence is because that number is released at the same time in both NYC and Chicago.
The ISM Manufacturing number is probably released on a low latency feed in NYC, and then takes 5-7 milliseconds, due to the speed of light, to reach Chicago. Either the clock used to release the ISM number was 15 milliseconds fast, or someone (correctly) jumped the gun.
Update: [...] The clock used to release the ISM was indeed, 15 milliseconds fast. This could be from using the default setting of many NTP clients, which allows the clock to drift up to about 16 milliseconds before adjusting time.
]]>ntp time synchronization spy trading stocks low-latency clocks internethttps://pinboard.in/https://pinboard.in/u:jm/b:c36c7599b498/