4 ms·

I wonder how many systems actually care? I presume the core NTP servers handle this well, and most systems just feed off of that? GPS satellites probably handl

by dgrin91 3mo ago

I wonder how many systems actually care? I presume the core NTP servers handle this well, and most systems just feed off of that? GPS satellites probably handle it well too, but maybe some consumer or even industrial GPS receivers don't? Maybe some trading systems? I don't think crypto systems care too much.

not-a-llm 3mo ago
traditional markets are closed when time changes happen
TrueDuality 3mo ago
The problem frequently crops up in order-deterministic systems that use time and haven't accounted for the edge case of all the vagaries related to time-keeping of this being only one. I've worked on some extremely sensitive systems that had thousands of lines of C dedicated to handling skewing a time gap across an hour-per-second when necessary. I know that code assumed only "missing" time (jump-forwards)... Even knowing what I know as a developer now, if I was re-implementing that system from scratch and didn't have this top-of-mind, I'd bet I would miss "overlapping" or "duplicate" time entirely. Maybe that is more of a me problem than others, but I'd bet there are some safety critical systems out there where the responsible engineers, QA, and specs all missed this as well.
netsharc 3mo ago
I wonder if there's things that run 24/7 and need to be monitored.. e.g. if you have oil flowing through some pipeline at 100 liters/second, one particular minute will have 6100 liters, and someone will want to get paid for that 100 extra liters. But the meter/reporting tool would say "Well, we measure every second, and the meter reported a constant rate of 100 liter/second, and as we know we have 60 seconds in a minute, so we got 6000 liters!". Or a database for "measurements every second for this minute" that has 60 fields, and don't have a field for the 61st measurement.
- blaze33 3mo ago
  I once worked with smart meters for electricity consumption that do run 24/7. Leap seconds were not an issue but we had a very similar one now that I think about it: DST shenanigans! Like how much time is there between 2 and 3 am? Usually one hour, but sometimes 2 and also sometimes 0. It looks simple at first but it creates a lot of edge cases that your business logic now needs to handle and we had a fairly complex system for this.
  - adev_ 3mo ago
    I can relate: My son is born at 02h30 right DST change time. It tooks 3 f*cking days to get his birth registered in the Hospital new birth registration system. The hospital (at the time) just got digitalized and most systems where not able to agree if he was born after or before DST changes. PS: I guess he is born fated to be a software QA later on.
    - netsharc 3mo ago
      This commenter says he has different birth dates in different countries' sytems, which is correct if you consider the exact time of birth, but... that's probably a bug? https://news.ycombinator.com/item?id=48853128 https://news.ycombinator.com/item?id=48853128
- imhoguy 3mo ago
  Now imagine blood pump during surgery.
  - enneff 3mo ago
    I’m horrified to imagine a blood pump or any life support system being network connected, or to rely on the precise time of day in order to function correctly. Accurate time keeping for anything in this realm can and should be done without a network.
    - imhoguy 3mo ago
wat10000 3mo ago
GPS uses its own time base that doesn't do leap seconds. For display purposes, the leap second offset to UTC is transmitted to the receivers and added to the displayed time if needed.
chaps 3mo ago
Systems definitely care, especially in finance and trading systems. Was involved in rolling out a large NTP annealing patch about ten years ago. We missed a couple and the effect was largely overall muted, but we did have one server with an old JVM hard crashing the server right at the second shift. That specific server was already hobbling along so it wasn't a surprise. But it required a bit of firefighting.

by dgrin91 3mo ago

not-a-llm 3mo ago

traditional markets are closed when time changes happen

TrueDuality 3mo ago

The problem frequently crops up in order-deterministic systems that use time and haven't accounted for the edge case of all the vagaries related to time-keeping of this being only one. I've worked on some extremely sensitive systems that had thousands of lines of C dedicated to handling skewing a time gap across an hour-per-second when necessary. I know that code assumed only "missing" time (jump-forwards)... Even knowing what I know as a developer now, if I was re-implementing that system from scratch and didn't have this top-of-mind, I'd bet I would miss "overlapping" or "duplicate" time entirely. Maybe that is more of a me problem than others, but I'd bet there are some safety critical systems out there where the responsible engineers, QA, and specs all missed this as well.

netsharc 3mo ago

I wonder if there's things that run 24/7 and need to be monitored.. e.g. if you have oil flowing through some pipeline at 100 liters/second, one particular minute will have 6100 liters, and someone will want to get paid for that 100 extra liters. But the meter/reporting tool would say "Well, we measure every second, and the meter reported a constant rate of 100 liter/second, and as we know we have 60 seconds in a minute, so we got 6000 liters!". Or a database for "measurements every second for this minute" that has 60 fields, and don't have a field for the 61st measurement.

blaze33 3mo ago
I once worked with smart meters for electricity consumption that do run 24/7. Leap seconds were not an issue but we had a very similar one now that I think about it: DST shenanigans! Like how much time is there between 2 and 3 am? Usually one hour, but sometimes 2 and also sometimes 0. It looks simple at first but it creates a lot of edge cases that your business logic now needs to handle and we had a fairly complex system for this.
- adev_ 3mo ago
  I can relate: My son is born at 02h30 right DST change time. It tooks 3 f*cking days to get his birth registered in the Hospital new birth registration system. The hospital (at the time) just got digitalized and most systems where not able to agree if he was born after or before DST changes. PS: I guess he is born fated to be a software QA later on.
  - netsharc 3mo ago
    This commenter says he has different birth dates in different countries' sytems, which is correct if you consider the exact time of birth, but... that's probably a bug? https://news.ycombinator.com/item?id=48853128 https://news.ycombinator.com/item?id=48853128
imhoguy 3mo ago
Now imagine blood pump during surgery.
- enneff 3mo ago
  I’m horrified to imagine a blood pump or any life support system being network connected, or to rely on the precise time of day in order to function correctly. Accurate time keeping for anything in this realm can and should be done without a network.
  - imhoguy 3mo ago

wat10000 3mo ago

GPS uses its own time base that doesn't do leap seconds. For display purposes, the leap second offset to UTC is transmitted to the receivers and added to the displayed time if needed.

chaps 3mo ago

Systems definitely care, especially in finance and trading systems. Was involved in rolling out a large NTP annealing patch about ten years ago. We missed a couple and the effect was largely overall muted, but we did have one server with an old JVM hard crashing the server right at the second shift. That specific server was already hobbling along so it wasn't a surprise. But it required a bit of firefighting.