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Comment by labster | Hacker News Reader

Can we take a longer hiatus on leap seconds, maybe 79 years or so, and only update once a century? Local apparent noon being off by 30 seconds or so has approximately zero impact on my daily life, but stupid things in datetime libraries do occasionally have impact. If we can’t throw off the oppression of UTC and greet TAI as liberators, at least adjust the clock at regular, very infrequent dates.

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Besides the sibling comment that some things rely on the days being synced to rotation, doing it once a century would pretty much guarantee that only the most obsessively robust systems would take it into consideration when being built.

We'd be giving ourselves a Y2k-equivalent to deal with every century. Maybe that's not the biggest deal in the world, but I still remember the last viscerally and we're already a fifth of the way to the next one (not to mention the timestamp bug one coming up in a decade).

I disagree with the other comment's suggestion that leap hours can be taken into consideration like DST. I see no reason why DST code (which is generally implemented as an extra timezone) could straightforwardly be adapted to handle a single permanent shift of time.

"If it hurts, do it more often" — Martin Fowler

Practice makes perfect. Release early, release often.

> I see no reason why DST code (which is generally implemented as an extra timezone) could straightforwardly be adapted to handle a single permanent shift of time.

The point is that we don't have to add the additional code to handle leap hours, as it can be implemented as a large swath of time zone changes.

We can imagine that there would be two versions of UTC, one before the leap hour (hereafter UTC) and one after the leap hour (hereafter UTC'). After the leap hour UTC and UTC' will coexist, where UTC' = UTC-1. Since time zone definitions themselves have UTC offsets, the trick is that instead of replacing all occurrences of UTC with UTC' (so that they would have UTC' offsets) we replace those offsets to have the same net effect. For example EST is UTC-5 before the leap hour and UTC'-5 = UTC-6 after the leap hour, so we pretend that the definition of EST changed to UTC-6.

Note that this approach essentially fixes the UTC-TAI offset (as opposed to the UTC'-TAI offset) and makes UNIX timestamp (time_t) deviate from the current version of UTC (well, UTC'). I believe this is just a matter of definition and thus much doable than changing UTC every few year. After all, leap hours would be much rare, probably the first one would occur at least a few centuries later.

The problem is not that changing the code is complicated. Changing code to accommodate four-digit years wasn't complicated. The problem is that you have to change every single piece of software which uses time. What you're proposing is exactly what I think needs to be avoided.

You would be right if vendors weren't able to deliver time zones in time. In practice they are, though with lots of headaches. We can just piggyback on the existing infrastructure of the time zone distribution with no additional cost.

I don't think this infrastructure you're relying on exists. A great deal of software isn't maintained at all. It was built once by a contractor and has been plodding along doing its work for decades.

Major software vendors won't have any particular trouble, but neither did they have any trouble in 2000. It's all the tail-end stuff which is in danger of breaking.

It should be very visible to users that softwares are unable to keep with time zone changes anyway (including those due to the relocation). If they are able to keep up somehow, probably manually, then leap hours don't impose any additional requirement to them.

Or, you can abolish the time zone to make software developers very happy [1]. At the expense of everything else.

[1] https://qntm.org/abolish

If you don't do any tzdata updates in a century then I can guarantee you that the application will be showing wrong local times anyways. Timezone changes happen. That is a already occurring thing.

And it's not like there is even hard deadline to do the changes, nor would it come unpredictably. If any schedule we set would seem problematic, the change can be deferred by another decade or two to get systems fixed if really needed.

> doing it once a century would pretty much guarantee that only the most obsessively robust systems would take it into consideration when being built.

tzdata updates happen all the time (in a relative sense). So code would need to handle those, and I don't see why potential leap hours couldn't be handled like that. Just means that Europe/London eventually will be +01:00 (or is it -01:00, anyways) instead of +00:00 its now.

Yes, I think that would make sense, but leap hours would be very rare: the first one won’t be needed for 500 years. See the first table at https://www.ucolick.org/~sla/leapsecs/dutc.html

But, leap hours don’t need to be co-ordinated: countries can and do change their clocks to adjust the time of sunrise when they want.

And leap hours will work much longer than leap seconds: leap seconds will become too frequent in 1 or 2 thousand years, but leap hours will just be getting started. See the second table at the same link https://www.ucolick.org/~sla/leapsecs/dutc.html

As a former developer of software for an international shipping company: Yup. They happen a lot more frequently than most people realise, I expect. Political reasons (e.g. neighbouring states [as in Sovereign] deciding to unify timezones), coups/wars suspending DST, and so on all usually result in some kind of adjustment, even if it's just the name of the timezone changing.

I can't speak to how different parts of society will interact in hundreds of years, but if today there were going to be a leap hour and programmers requested that we start considering London to be in +01:00, the chances of politicians or public agreeing with that request is nil.

Sure, we will randomly move the end of the DST from the last Sunday of October to the first Sunday of November and everyone will try to kill us, right? DST is the perfect example that we have a relative freedom in changing time zone offsets.

You are however right that this is a political matter requiring some (but I believe, reasonable) amount of coordination, but timekeeping is in many parts political anyway. Practically speaking countries would implement the change out of necessity and not because of agreements, as one hour deviation is significant enough.

> we have a relative freedom in changing time zone offsets

Who is we in this sentence? Programmers certainly don't, they have to report times and timezones in their software as the populace expects it to be reported. Governments can change timezones, but they're not going to, because the political cost of telling everyone that they're in a new timezone is greater than the political cost of telling programmers where to shove it.

Most of the public will see absolutely no reason why they should have to permanently change the timezone they're in for the sake of a one-time event. And honestly, even as a programmer who'd be doing the fixing, I agree that they're right.

Governments absolutely can. The updates to tzdata [1] are full of arbitrary changes happening all around the globe, not just for a few weird countries. The example I quoted above is 2007 changes to the United State's DST and a perfect example that governments can push time zone changes with at most marginal perceived benefits. Also remember that the current proposal to abolish leap seconds itself was primarily arosen due to computing complications anyway. Programmers can (indirectly) affect the future of leap seconds than probably any other group else.

[1] https://github.com/eggert/tz/blob/master/NEWS

Russia decided to just stay on DST with 6 weeks notice a few years ago, thereby instantly creating half a dozen new timezones. And now they're discussing going back to normal time/DST...

I don't see a single thing different between leap hour and DST switch. Especially since Europe wants to cancel DST it wont even be something which happens periodically forever

> Besides the sibling comment that some things rely on the days being synced to rotation

Examples would be great. Especially examples of things relying civil time to track rotation.

People who can't cope with leap seconds should stop pestering the people who define UTC and just switch to TAI. They can do that now. No one is stopping them. Leap seconds are a pain and I myself would happily choose TAI over UTC for the system clock on a typical embedded system.

However, for civil time keeping and for some technical purposes, UTC as currently defined is exactly what we need. Don't fuck with it.

No, they can't.

Programmers have to deal with the outside world. The outside world has timezones defined as offsets from UTC. So when UTC changes, the whole world changes their clocks, and programmers have to cope. If your program doesn't agree with that world about what time it is, your program will get blamed.

If it was a choice that I could individually make, I would tell astronomers to go pound sand. But it isn't. By historical happenstance, they have been put in charge of time, and it is truly a question of the tail wagging the dog when they care about a 1 second deviation between UTC and the position of the sun at a particular longitude.

Why not derive UTC from TAI (via a table of leap seconds)? Then apply the TZ rules to DST to arrive at local time.

The short answer is that I don't do this because I'm not insane.

Think about it. How much software would I have to rewrite to make this possible? What value does that rewrite create? And will maintenance programmers thank me for it? Will it get adopted?

As a programmer I have to interact with databases, operating systems, various libraries in various languages, and so on. Frequently with quick switching between them. ALL are written assuming UTC. Shall I name myself Don Quixote and spend the rest of my life on a rewrite that nobody wants to us?

Just to give a sense, I recently had to do some data science tasks. Data was in Postgres, my code was in Python, using pandas for speed, and pandas is built on numpy. All four of those have their own datetime library, and I had to deal with all four of them. If I followed your suggestion, before I did any work I'd have to rewrite all 4 libraries, and then figure out how to replace Amazon RDS because it doesn't support my "improved Postgres".

And if I did all of that, I've not changed the odds of something like https://www.wired.com/2012/07/leap-second-glitch-explained/ happening again and taking down my favorite websites for a while. Because guess what, they won't be running my super-duper rewritten code.

I feel the solution is for the programming community to slowly and methodically move towards using TAI in basic infrastructure (operating systems, routers, NTP etc) and build a base on which to derive the civil timekeeping (UTC + localtime, DST etc).

That, or get involved in the standards work. That said, after ruining observations by sending a bunch of satellites into space, tech people might be even less popular than before in the astro community...

Edit I just got around to reading that Wired article and... ugh

> Reddit was just one of several web outfits that were hit by leap second glitches just after midnight Greenwich Mean Time on Saturday,

Article is from Jul 2012, GMT was not in effect at that time. I guess they meant UTC, but if tech journalists don't know that GMT is depreciated as a concept of "universal time" what hope is there for meaningful time reform...

Do you have any idea how much work it is to rewrite all of that software?

The solution people are actually moving to is https://developers.google.com/time/smear. The downside is that measurements of elapsed time will be off in that day. But no rewrite needed, and most applications are going to be just fine with that.

Timezones may have multiple names. Greenwich Mean Time and Zulu, aka GMT and Z, are officially defined timezones that happen to be UTC+0. Both are in widespread use and are not wrong.

There’s an ambiguity in that GMT is a civil timezone that in the UK is BST when DST is in effect. UTC cannot be affected by DST.

I hear a lot of Brits calling their time “GMT” even when DST is in effect. It’s a shorthand for “current time in the UK”. Hence, ambiguous.

> However, for civil time keeping and for some technical purposes, UTC as currently defined is exactly what we need. Don't fuck with it.

You are asserting that without any justification. I see no benefits and lots of downsides in having leap seconds in civil time specifically.

I think that the point is that for most definitions of "civil timekeeping" you just do what Unix does and ignore the leap seconds altogether and simply live with the fact that once in a while one wall-clock second takes two SI seconds (or does not exist at all), probably by simply being completely oblivious to that fact.

Don't even get me started on UNIX time. On that I agree with the parent comment, whatever the time scale, you shouldn't fuck with it. Alas, UNIX is what it is..

I'm a diehard proponent of leap hours [1]. We already have a regular (or, rather irregular) adjustment in the civil time, namely time zones and "daylight saving" times. While I passionately hate DST, if we have to have DST anyway it's much better to make UTC adjustments use the same increment as well.

[1] http://www.leapsecond.com/LEAPHOUR/

> If we can’t throw off the oppression of UTC and greet TAI as liberators, at least adjust the clock at regular, very infrequent dates.

Why not just use TAI for almost everything and leave UTC (including regular leap seconds) for applications that need it?

The more infrequent your deployments, the more difficult they will be.

How does TAI relate to Epoch time?

More and more I use Epoch time for most things just because of how convenient it is.

I rarely need sub-second granularity, and it's just one number, so it's sortable, math-able, etc.

Then whoever is doing the display can convert it any way they want to.

Remember that your code needs to account for the possibility of a negative leap second, meaning if you're using epoch time for timestamps you could have an instance that an event that happened after a previous one could be stamped as having happened before it instead.

https://en.wikipedia.org/wiki/Leap_second

Edit: Actually I was slightly wrong, in the event of a leap second, we would repeat the same second twice.

Thank you for the heads-up!

I try to write code loose enough that this would not be a problem. :)

Can we take this solved problem and replace it with a new one that has details we haven't figured out?

Pretty sure there are lots of things that you use everyday that actually require precision time, such as GPS.

GPS does not use leap seconds. See e.g. https://en.wikipedia.org/wiki/Global_Positioning_System#Leap...

Leap seconds have nothing to do with precision time. It's a non-periodic alteration to the definition of UTC. Those niche applications that require second-accurate knowledge of Earth's rotational accuracy don't need to rely on leap second changes to UTC; they could get that information out of band, and will need to anyway when they need sub-second accuracy. The 99.999% of other applications that don't need to know Earth's rotation orientation relative to the sun within a second -- but do have to calculate time differences between two UTC times -- would be much better off not having to deal with leap seconds. Leap seconds were a terribly misguided idea.

> Leap seconds were a terribly misguided idea.

I prefer dropping leap seconds, but I wouldn't call them misguided. UTC and leap seconds come from maritime celestial navigation, where tracking rotation is actually important. Civil time then just piggybacked on that, which at the time probably was perfectly reasonable solution.

A detailed look at the negotiations that led to leap seconds shows that they were not for maritime celestial navigation. During the process several different times the celestial navigation folks set a limit on how far radio broadcast time signals could deviate from astronomical time, and every one of those limits was violated as the negotiations proceeded. By the time the draft recommendation was given to 12th Plenary Assembly of the CCIR it allowed for leaps of multiple seconds, and that draft was amended on the floor to leaps of only one second before they voted to approve.

Precision isn't a binary, it's a continuum. The question at hand is whether there are significant use cases where 1 second of slack in matching the Earth's rotation is acceptable, but 30 seconds is too much.

GPS isn't an example of that because 1 second is already a quarter mile off.

Pretty much all telescopes (under computer/time control) on this planet rely on UTC being quite close to UT1, since every second difference leads to a 15 arcsecond error in the pointing of the telescope (error between where you want to point the telescope on the sky and where you are actually pointing).

While <5s is usually not a problem (except for some instruments with very very small FoV), at 30s it really becomes a problem for instruments with modest fields of view.

I would think this is an argument for telescopes using UT1, not whether UTC should be adjusted for leap seconds. This is such a fringe application and all involved are aware of the issue, that I don't think it's relevant here at all.

UTC is defined to be within 1s of mean solar time at 0deg longitude (= UT1).

If leap seconds are a problem for the intended application then UTC is the wrong thing to use. There are other scales that are defined differently that can be used in it's place (such as TAI).

However if exact frequency is not critical one could also directly use UT1 instead of UTC (people that use leap second smearing for instance should have no issue with that..).

GPS time is already immune from leap seconds. It has a fixed offset from TAI of 19 seconds and always will.

It also contains UTC offset information so that you can derive the current UTC time from GPS if you wanted to.

As long as everyone agrees on the time GPS will work. It's a question of how much deviance from solar time we are willing to tolerate vs how much effort we want to tolerate.

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