4 ms·

Google's proposal is a smear. [1] Most time servers do not use smear. No idea what behavior it may introduce in places where sub-second time is important. Cu

by Bender 4mo ago

Google's proposal is a smear. [1] Most time servers do not use smear. No idea what behavior it may introduce in places where sub-second time is important. Curious if all these bugs [2] were fixed specifically to deal with going backwards. [1] - https://developers.google.com/time/smear https://developers.google.com/time/smear [2] - https://rivassec.com/leap-second-chaos-2012.html https://rivassec.com/leap-second-chaos-2012.html

yen223 4mo ago
The brilliant thing about the smear is that it distributes the new second across each second of the day, so that each second differed by 1/86400 seconds, well within the margin of error for NTP. As far as the computers were concerned, nothing was different.
- toast0 4mo ago
  The less brilliant thing about the smear is that if your ntpd syncs from smeared and unsmeared servers, the results aren't great. It would have been better if they would have kept the time on the wire accurate or added mandatory protocol stuff to avoid confusing things for ntpds configured to different leap second handling.
  - not-a-llm 4mo ago
    if you need below 1 millisecond time accuracy, probably you know what you are doing and you wont mix NTP servers (and I think you need PTP for that)
    - chaps 4mo ago
      You'd think so. Legacy servers that've been running for ten years really puts a hitch in that.
    - lesam 4mo ago
      Until you work in financial markets and you want to measure latency vs a bunch of other servers you don't own, all of whom pick different smears (and some of whom aren't sure in advance which smears).
      - not-a-llm 4mo ago
        financial markets dont trade when the smears happen (NYE)
        _alternator_ 4mo ago
        They can happen mid-year too. They usually don't for this reason, but they can.
        weakened_malloc 4mo ago
        Depends on the market. Crypto and prediction markets wont stop.
        lesam 4mo ago
        Early in my career, I had to babysit our FX quoting app through the July 2015 leap second. And some things do trade 24/7 (though I wish they wouldn't, one auction per minute during US east coast business hours would be totally sufficient for most US markets).
  - ikiris 4mo ago
    User error
  - lozf 4mo ago
    Better still, if Unix time tracked TAI (monotonically increasing every SI second), and Leap Seconds were handled in a distributed database much like time zones - possibly even the same one we all use anyway.
ikiris 4mo ago
Yeah 90% of the time the simple solution is just use Google time and these problems are smeared away because they got burned enough internally they did it themselves
eqvinox 4mo ago
Leap smearing is amazing exactly until the moment you need to know whether you're leap smearing (because your seconds are 1.0000116s long, or the reverse). That instant, it turns from amazing into the worst godawful mess you can imagine. Leap seconds can be stored and communicated, if you need it you can do the work and get it. Leap smearing, you're shit out of luck, especially if you're a developer and need to deal with systems operated by others. If you're sure you'll never cross that moment and need to know you're in a smear, go ahead, it's great. Otherwise test yo' stuff with leap seconds and get bugs reported & fixed.

by Bender 4mo ago

yen223 4mo ago

The brilliant thing about the smear is that it distributes the new second across each second of the day, so that each second differed by 1/86400 seconds, well within the margin of error for NTP. As far as the computers were concerned, nothing was different.

toast0 4mo ago
The less brilliant thing about the smear is that if your ntpd syncs from smeared and unsmeared servers, the results aren't great. It would have been better if they would have kept the time on the wire accurate or added mandatory protocol stuff to avoid confusing things for ntpds configured to different leap second handling.
- not-a-llm 4mo ago
  if you need below 1 millisecond time accuracy, probably you know what you are doing and you wont mix NTP servers (and I think you need PTP for that)
  - chaps 4mo ago
    You'd think so. Legacy servers that've been running for ten years really puts a hitch in that.
  - lesam 4mo ago
    Until you work in financial markets and you want to measure latency vs a bunch of other servers you don't own, all of whom pick different smears (and some of whom aren't sure in advance which smears).
    - not-a-llm 4mo ago
      financial markets dont trade when the smears happen (NYE)
      - _alternator_ 4mo ago
        They can happen mid-year too. They usually don't for this reason, but they can.
      - weakened_malloc 4mo ago
        Depends on the market. Crypto and prediction markets wont stop.
      - lesam 4mo ago
        Early in my career, I had to babysit our FX quoting app through the July 2015 leap second. And some things do trade 24/7 (though I wish they wouldn't, one auction per minute during US east coast business hours would be totally sufficient for most US markets).
- ikiris 4mo ago
  User error
- lozf 4mo ago
  Better still, if Unix time tracked TAI (monotonically increasing every SI second), and Leap Seconds were handled in a distributed database much like time zones - possibly even the same one we all use anyway.

ikiris 4mo ago

Yeah 90% of the time the simple solution is just use Google time and these problems are smeared away because they got burned enough internally they did it themselves

eqvinox 4mo ago

Leap smearing is amazing exactly until the moment you need to know whether you're leap smearing (because your seconds are 1.0000116s long, or the reverse). That instant, it turns from amazing into the worst godawful mess you can imagine. Leap seconds can be stored and communicated, if you need it you can do the work and get it. Leap smearing, you're shit out of luck, especially if you're a developer and need to deal with systems operated by others. If you're sure you'll never cross that moment and need to know you're in a smear, go ahead, it's great. Otherwise test yo' stuff with leap seconds and get bugs reported & fixed.