8 ms·
Leap Smear
- gmrple 5y agoWhy? Why don’t we use TAI or GPS time for generic world wide coordinated computer time?
- shadowgovt 5y agoAmong other reasons (and in line with why Google cares to keep things tied to astronomical time measurments instead of perfect-period atomic clock measurements): if a user schedules something to happen at 'noon every day', they become dissatisfied if the timing of the event begins to drift off of "sun overhead" time consistently because of leap seconds.
- toast0 5y agoSun overhead time drifts around throughout the year anyway, a couple of seconds is much less of a difference than the difference due to seasons and much less than DST. For example, solar noon is 1:15pm today in Seattle, and will be 1:09pm at the end of the month. Way more variability than the accumulated leap seconds over a century.
- dharmab 5y agoThere are very few times and places on earth where the sun is directly overhead at noon. For example, solar noon is at a different time depending on where within a time zone you live, as well as the time of year.
- midasuni 5y agoWhere within a city even. Solar noon in london varies by over two minutes depending which end of the district line you are - that’s 5 times the error “corrected” by leap seconds over the last 50 years.
- dharmab 5y agoThe shortest possible TL;DR of https://en.wikipedia.org/wiki/Leap_second#History https://en.wikipedia.org/wiki/Leap_second#History appears to be "because TV and radio broadcast systems in the 1950s were based on solar time rather than astronomical time and wanted to stay in sync to each other." There seems to have been a movement against leap seconds: https://en.wikipedia.org/wiki/Leap_second#International_proposals_for_elimination_of_leap_seconds https://en.wikipedia.org/wiki/Leap_second#International_prop...
- 3pt14159 5y agoI know. I know. It's bananas. People keep making time more and more complicated. Different kinds of smears, changes in the dates of daylight savings times, timezone shapes influenced by geography instead of the amount of light.
- shadowgovt 5y agoHonestly, time is complicated. Even on Earth, where we rarely have to address synchronization errors due to relativistic effects. Users care very much about time preserving ordering of events and synchronization of events at disparate locales. They get grumpy if, say, their alarms start going off at what the local restaurants think is 1PM instead of noon because the national government passed a law starting (or stopping) observance of Daylight Savings this year. Similarly (though it's a slower-rolling error), they get grumpy if their alarms start firing at 11:59 and 59 seconds, 11:59 and 58 seconds, etc. when they have them set for noon. Time is, ultimately, a human construct and software management of it is beholden to the need to get it right from the user's point of view.
- 3pt14159 5y agoYou were downvoted unjustly. I think your opinion is mostly valid, but I think people undervalue simplicity because they underestimate knock-on effects of their decisions.
- creeble 5y agoIt depends on what you mean by "computer time". We _do_ use it on some "computers": > "The Society of Motion Picture and Television Engineers (SMPTE) video/audio industry standards body selected TAI for deriving timestamps of media.[77] IEC/IEEE 60802 (Time sensitive networks) specifies TAI for all operations. Grid automation is planning to switch to TAI for global distribution of events in electrical grids. Bluetooth mesh networking also uses TAI.[78]" (from https://en.wikipedia.org/wiki/Leap_second#Workarounds_for_leap_second_problems https://en.wikipedia.org/wiki/Leap_second#Workarounds_for_le... )
- aidenn0 5y agoBecause we want to unambiguously refer to times in the future? [edit] It would of course have been possible to have NTP be based of of TAI rather than UTC (and that might have been a good idea), but it still begs the question of what any POSIX operating system will do given that posix timestamps are leap-second adjusted. And the reason that POSIX timestamps are leap-second adjusted is so that 2628198843 has always, and will always represent 2053-04-13T23:14:03Z. For better or worse, humans have standardized on UTC, so machines that expect to interact with humans must also do so.
- dmm 5y agoI would argue UTC timestamps are still ambiguous, just in a different way. How many seconds between now and 2038-01-01T00:00:00? It's impossible to say because we can't predict future leap seconds. Many uses of future times are always going to be ambiguous because humans care about timezones, which can change at any time.
- aidenn0 5y agoThat is true, but again humans. Humans will be less bothered by you being off by 10s of seconds for "how many seconds until X" where X is multiple years in the future than they will be where X is a minute in the future. Any timestamp created today may be used far in the future, but durations are (by their very nature) transient. Even if you were to do a sleep(nominal seconds until 2038) the computer is likely to reboot before the interval expires, mooting any issues.
- tshaddox 5y agoThat’s not ambiguous though. The answer is, unambiguously, that we don’t know how many seconds there will be. But we can still agree to meet at that time, assuming we will both continue using the same time standard.
- Closi 5y agoI get OPs point though - coming from an outsiders perspective I would have thought that a key feature of a time format would be to know how much time there is between two other times.
- gopalv 5y ago> Why don’t we use TAI or GPS time for generic world wide coordinated computer time? I think that is valid as long as systems are talking to systems, but the interface with the world (when things are happening in the world) is where the solar day or year is still relevant. I'm sort of joking, but watching Interstellar made me kinda cringe about what interstellar gravity wells is going to do to time-keeping, even if we use something like an atomic clock to keep time. We will slowly get better at this until we discover something new, but the switch doesn't mean anything until the costs outweigh the change. And the leap second is going look like 46-45 BCE[1]. [1] - https://www.youtube.com/watch?v=fD-R35DSSZY https://www.youtube.com/watch?v=fD-R35DSSZY
- repsilat 5y agoIn some polls I've seen there's plurality support for "permanent 'summer time'". People don't seem to care much that noon in civil time maps exactly to the sun being at its peak. Leap second drift is super slow, too -- IIRC something like 10 minutes per millennium. If we shift our clocks by an hour in the year 8000 I think that's less disruptive than leap seconds every year or so.
- denton-scratch 5y agoGPS time is no use for far in the future (TAI is OK). Imagine someone 2,000 years in the future, discovering an archive containing exact GPS timestamps for events. There is no reason to suppose that our present GPS system will still exist - so these timestamps won't be much use to them, since they won't know what the present time (their present) is in terms of GPS. The timestamps in the archive will no longer be precise, as far as they're concerned.
- dmitriid 5y agoAs others pointed out: 1. because we want monotonously increasing time on our computer systems. 2. because software deals with leap anything very badly 3. [not mentioned]: we are in danger of running into negative leap seconds very soon: https://twitter.com/ariadneconill/status/1422163289518313474 https://twitter.com/ariadneconill/status/1422163289518313474
- nonfamous 5y agoInterestingly, you can accommodate negative leap seconds with smears as well. FTA: >> A negative leap second, if one were ever to occur, would be smeared by speeding up clocks over the 86,399 SI seconds from noon to noon.
- Gibbon1 5y agoWhat I've seen with embedded systems is you have a real time clock. And the system when it updates the time updates the registers in the real time clock. And then bad things always happen sooner or later I've always just let the thing run and use an offset to calculate 'users local time'. If the time gets updated I update the offset. I think that's what programmers want[1]. Instead of the current system system where the primary time unpredictably jumps around. [1] For time of day programmers probably want a standard formula that takes an offset and a rate to output the time of day.
- deleted 5y ago[deleted]
- thedream 5y agoCharlatans will forever depend on hacks and falsehoods in their attempts to supplant The Creator. Matthew 24:36 -- "But of that day and hour knoweth no man, no, not the angels of heaven, but my Father only."
- johnklos 5y agoGoogle always seems to want to fix symptoms while ignoring problems.
- vlovich123 5y agoOr, from a different perspective, Google chooses to build a robust system that can paper over defects because human error is common, hard to test, & hard to detect when it comes to time AND the consequence of errors is a massive company wide outage.
- LeoPanthera 5y agoThe following is a bit of a rant so I apologize in advance. I'm not a programmer, but I understand enough about systems administration to know why monotonic time is important. But leap seconds exist for a reason - the rate of Earth's spin is not constant, so since the invention of clocks accurate enough to be able to tell that, we have had to invent a way of compensating for the variable rate of spin such that "midday" is still the middle of the day and "midnight" is still the middle of the night. Without adjustment, these concepts would slowly drift. It makes me angry that programmers feel that they "own" the concept of time measurement enough to propose the abolition of leap seconds. The definition of unix time excluding leap seconds is really the origin of this nonsense, and it has always seemed to me that the obvious solution is computers should simply measure seconds since the epoch. Wikipedia describes this version as the "TAI-based variant" of Unix Time, and if we all used it, computers wouldn't even have to care about leap seconds, and conversion to standard time display could be done in userland, accounting for leap seconds in the process. Civil time is more important than keeping your log files in order. Get your computers to count seconds, and leave more important human concepts like midday and midnight to the humans who are affected by them.
- humanistbot 5y ago> It makes me angry that programmers feel that they "own" the concept of time measurement Programmers feel that they "own" pretty much every social construct, by virtue of the fact that it is their job to encode those constructs into interfaces and databases. See the famous "falsehoods programmers believe about X" [1] --- and I'm sure you'll like this one about time [2]. [1] https://github.com/kdeldycke/awesome-falsehood https://github.com/kdeldycke/awesome-falsehood [2] https://infiniteundo.com/post/25326999628/falsehoods-programmers-believe-about-time https://infiniteundo.com/post/25326999628/falsehoods-program...
- shkkmo 5y agoMy understanding is that the rate of earth's spin is "constant" (actually it is slowly decreasing on geologic time scales) but the orbit of the earth is not circular and a revolution around the sun doesn't match with a full number of earth rotations.
- motohagiography 5y agoThis sounds like a potential flash trading arbitrage play between code that implements the smear and code that doesn't. As in a whole bunch of market making institutions and retail traders are going to be a few hundred milliseconds slow off the mark that day? Speculating you may get a few extra tries guessing a PIN as well given the time based window shift, we might be able to see evidence of the drift in internet routing tables and back off penalties, the same might go for some buggy rate limiting implementations for web requests, where the number of requests you can get through in a "minute" will overflow a fixed integer value. I'm sure the blockchain DeFi people are already hunting through smart contracts for potential vulnerabilities on it. This is a really interesting problem, even if these ideas are speculative, it's where I'd go looking for vulns.
- ncmncm 5y agoThis is the worst of all possible worlds. Instead of a disruptive event that lasts 1 second, it lasts 86400 seconds. All throughout those 86400 seconds you are out of sync with everybody else in the world, except those few you might have bullied into matching you. The best solution is to simply cut UTC loose from astronomical time. Anybody who cares about astronomical time--people calculating orbits and telescope directions--are not using UTC anyway, and know how to convert from TAI when they need to. Over two centuries, UTC might drift a minute off of astronomical time. A UTC2 in 2106 (when 32-bit unsigned count of seconds since 1970 rolls over) would be a good point to plan for a correction, if one starts to seem warranted by then. In the meantime, you just treat UTC as if it really did represent astronomical time, and with the TAI crowd out of the building, no one is left to care about the difference. It is easy to institute the change: simply stop declaring leap seconds. At each international treaty-scheduled opportunity, say "nope". And announce you will always say "nope". Until the correct solution is ratified, getting your leap second over-with in a second is the next best thing.
- wmf 5y agoNo, I think stock exchanges going down is worse than smearing. The <500 msec difference between smeared time and UTC is barely noticeable due to network latency.
- ncmncm 5y agoStock exchanges shutting down for a few seconds to let the storm abate is pretty benign. Exchanges stop trading, for much longer, for a variety of good reasons. "Time Standards are insane" is one such good reason among many. The only real harm that can arise is if trading halts for some users but not others. If all trading stops, the field remains level.
- midasuni 5y agoWhy are we happy to have clocks drift by a second? Why not have leap milliseconds or leap nanoseconds? Or conversely leap minutes or hours? 1 second changes seem arbitrary
- GranularRecipe 5y agoSecond is the SI base unit of time. Whether it makes sense is a different question, but it is not "arbitrary".