Responding to a deleted comment:
> ... the "invisible infrastructure" of the web; balancing historical accuracy with the technical need to minimize zone fragmentation is a much more complex trade-off than it appears on the surface ...
The complexity goes up tremendously if some condition is rarely encountered: eg leap second. This means it gets pushed to a "corner case" and tested more lightly and more rarely.
At $work around 2014 we had three different hardware GPS types which we used for precision timekeeping; some chips, daughterboards, and firmware. One day a leap second arrived -- it gets broadcast to aGPS hardware a day ahead of time -- and all three implementations handled it differently. One handled it, one did something else like ignore it, and I think one even bricked itself. That situation was less than bueno.
> The complexity goes up tremendously if some condition is rarely encountered: eg leap second. This means it gets pushed to a "corner case" and tested more lightly and more rarely.
There is some talk of eliminating the leap second, which would over time have the Earth and sun diverge with regards to noon and such. One 'answer' to this concern is to have a 'leap hour' or something in the future (some future generation's problem, not ours): but given that people can't even get February 29th correct now, and it happens regularly, I don't see how a one-off event would be made to work. It'd be a huge coördination problem.
Just look at the introduction of the Gregorian calendar: it was slightly off since the time of Julius Caesar, but that minor error added up over time, to the point that to get the equinoxes/solstices back to where they 'should' be 10 days had to be removed with the Gregorian calendar. And because of politics (or a religious flavour) it took a long while for everyone to get on the same page.
> One 'answer' to this concern is to have a 'leap hour' or something in the future
We've had 27 leapseconds in the last 54 years [1] - an average of 0.5 seconds per year.
At that rate, solar time will drift by 60 seconds over the course of 120 years. Drifting by 10 minutes will take 1200 years.
The leap hour will be in 7200 years, around year 9226.
> The leap hour will be in 7200 years, around year 9226.
7200 years ago the Neolithic revolution was still in full swing and many of the most famous megaliths like Stonehenge hadn’t even been built yet. The first real state, the Sumerian civilization, hadn’t formed yet in Mesopotamia.
Personally, I’m very comfortable making this someone else’s problems 7200 years from now. If they’re still having basic coordination issues then it’s their own damn problem.
"Basic" made me lol :)
Yeah. There’s also the issue that the earth’s rotation is slowing down, so over the long term leap seconds would become more and more frequent. There’s a point when the earth is slow enough that leap seconds need to happen nearly every month, and by that point they are no longer a workable solution to the problem. That is expected to take a few thousand years, comparable to the point where a leap hour would be needed if there were no leap seconds.
>There is some talk of eliminating the leap second
The concern, of course, is that some universes eliminating them while others don't can puts us out of sync. This creates a wobble that could potentially throw us out of Hilbert space.
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In British Colombia they’re locking into daylight savings time, so I think it’s safe to say that people aren’t really bothered by solar accuracy.
The calendar adjustments are because the planet's constant orbital period isn't a whole number of days.
The leap seconds were an attempt to have wall clock time map to the planet's rotational angle consistently despite the problem that the planet's spin varies unpredictably.
Yes the "leap hour" is a legal fiction of course. In reality in the event anybody cares about this in the distant future they will make the kind of "drastic" changes you've probably experienced twice a year for your whole life and barely noticed... More likely because the drift is so incredibly slow they won't change anything.
So lunar tidal forces are slowing the rotation, but (recently?) Earth mantle/core is causing a speed up, but climate change and melting ice is contributing to the slow down side:
* https://www.scientificamerican.com/article/leap-seconds-may-...
* https://scripps.ucsd.edu/news/global-warming-influencing-glo...
The general trend is slowing down. Apparently (?) once the day gets to be 24h+0.001sec (+1 millisecond), a leap second would occur about every 1000 days; then when it becomes 24h+0.002sec, a leap second would occur about every 500 days; when it reaches 24h+0.003sec, a leap second would occur about every year; etc.
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Leap seconds have so many problems beyond the time adjustment. It's a small/odd enough adjustment interval that there are wildly different approaches like leap smears. On top of being so small, it's rare enough (~every 2 years), depending on how a system is used, lack of proper handling might not be obviously apparent or lack of obvious problem in one implementation ignoring it may lead to lack of care in another implementation which would have a problem ignoring it.
Leap hour replaces all of that with what is more or less equivalent to a change in DST rules (except for more time zones at once). DST changes don't go perfect either by any means... but we do them regularly enough without the world crashing down that doing an additional shift change of an extra hour every 5000 years is almost certainly less hassle and breakage than the leap second approach breaking things every ~2 years.
It is way more easy to let UTC (without leap seconds) just drift away from the zero meridian and move countries to different time zones when convenient. We mess around with daylight savings time often enough that nobody will notice if we have change local time every couple of thousand years.
DST changes are pre-scheduled. Throwing a random hour in/out at (say) June 30, 2029 may be something else. Unless the jump is treated as a TZ change in tzdata?
Yeah you treat it as a time zone change where every zone moves over (or every country moves to the adjacent zone maybe). You can schedule it N years in advance. It's definitely not 0 disruption, but it's very manageable. Regions change TZs or toggle DST frequently enough that we can handle it.
IMHO the correct way to handle leap seconds would have been at the same layer as timezones, i.e. a display-only thing. Timezone databases are regularly updated, you push out leap second updates there. In the worst case, people's clocks are off by one second but all the underlying timing logic doesn't crash.
you can use TAI (international atomic time, basically UTC without leap seconds) if you want to be serious about it
I'm a fan but it's rare for anyone else to agree!
I fully expect in such a regime, people would be complaining about how the leap second insertion caused their recurring meeting to shift from 9am to 8:59:59
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> There is some talk of eliminating the leap second, which would over time have the Earth and sun diverge with regards to noon and such.
<rant> It won't happen on a human scale. So why oh why do we screw around with this moronic leap-second nonsense ? Oh dear, in the year 4000 noon will arrive three minutes earlier compared to now. So? </rant>
We had a leap hour yesterday...
> We had a leap hour yesterday...
Prescheduled.
Now tell everyone we're having one June 30, 2029, and see how things go.
If we eliminate leap seconds, we'll need a leap hour in ~500 years. It could be announced 50 years in advance.
> It could be announced 50 years in advance.
Which is about how long it took for folks to switch from the Julian to the Gregorian calendar.
It took much longer than that, although to be fair the Catholic countries had switched in much sooner than 50 years.
In the US DST was changed in 2005 and the change went into effect in 2007.
> There is some talk of eliminating the leap second, which would over time have the Earth and sun diverge with regards to noon and such
“Over time” really glosses over how much time it would take. In 500 years there might be half as much divergence between solar noon and 12:00pm as we intentionally inflict on ourselves with DST, or that France and Spain inflicted on themselves in the 1940’s so they could share a time zone with Germany. By the time anyone will even notice we will probably change time systems for other reasons anyway. It’s not even remotely comparable to the Julian/Gregorian issue, which dealt with leap days. Each day has 86400 seconds.
If you think you're going to steal days off my life, you've got another thing coming buster!
Just here to reinforce your point.
The last leap-second I encountered (also the 2014 one) crashed my MySQL databases.
you wouldn't assume that it depends on time like that, because honestly why would it? "surely it's fine, NTP corrects drift of a second fairly frequently"- but a leap second is not a drift, it's something quite insane unless your primitives are solid. Nobody would test for this.
Yes I would assume that the NTP daemon would handle a leap second arrival with guarantees of (1) gradual application over a longer period and (2) never moving the clock backwards, only slowing it a little.
I wonder if all NTP implementations don't follow those guarantees?
Oh and another app that hates clock jumps used to be sshd; it would just bail out and drop all connections. We found that out while chasing ANOTHER bug in SunOS on a T4: they didn't have it mutexed right so it possible to read its RTC register while it was in the middle of getting updated so the client would read a garbage time. We chased NTP for a week before realizing it was the kernel.
The insanity is that both NTP and unix timestamps need to be wound back during a leap second, as well as computer hardware clocks. If we just had monotonic clocks everwhere and adjusted for leap seconds in presentation then we wouldn't have many of the associated problems.
It's not like we wound back by 24 hours on leap days, that would be insanity. So in addition of leapseconds being a rare problem, it's also handled in a uniquely bad way.
