[154401] in North American Network Operators' Group
Re: F-ckin Leap Seconds, how do they work?
daemon@ATHENA.MIT.EDU (Owen DeLong)
Tue Jul 3 15:52:14 2012
From: Owen DeLong <owen@delong.com>
In-Reply-To: <20120703175905.GA15977@pob.ytti.fi>
Date: Tue, 3 Jul 2012 12:46:34 -0700
To: Saku Ytti <saku@ytti.fi>
Cc: nanog@nanog.org
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
On Jul 3, 2012, at 10:59 AM, Saku Ytti wrote:
> On (2012-07-03 10:11 -0700), Owen DeLong wrote:
>=20
>> Trading one known set of bugs for a (probably) larger set of unknown =
bugs is not my definition of progress. Cost without progress is harmful =
and should be avoided.
>=20
> Leap bugs are NOT known. Most people have no idea unixtime is not
> monotonically increasing.
> I had no idea myself until sunday, I had assumed we really go 59 -> 60 =
->
> 00, but we go 59 -> 59 -> 00. So 59.1 can happen before or after 59.2.
> To me this is fundamentally and inherently broken.
>=20
> It's quite hard to find code which stores timestamp and then compares =
it in
> future to timestamp which assumes time can travel backwards.
> Most bugs are just things that should last 5s last 6s or 4s, but =
certainly
> the bugs exist and developers were not aware that they exist.
>=20
>=20
> --=20
> ++ytti
If you don't know that time is not monotonically increasing, then that =
only becomes a software bug when you codify your own ignorance into =
software you write.
It is well known that leap seconds exist.
The rotation of the planet does not line up well with the orbit of the =
planet and neither of these lines up particularly well with the rotation =
and orbit of the moon.
Since we have a long standing tradition of using the orbit of the earth =
to determine years and the orbit of the moon to divide years into =
months, we use some fudge-factors on the months to make years and months =
line up. (12 true months would leave us several days short of a complete =
orbit at the end of the year and seasons would migrate.)
Since we have a tradition of measuring diurnal and other repetitive =
cycles (days) based on the rotation of the earth, we end up with fudge =
factors to make that line up with months from time to time. (leap =
seconds).
So it goes. Time is much more complex than many people realize. If you =
write software where time matters, it is your responsibility to learn =
about these things.
Owen
