5 ms·
For future leap seconds, Google (including GCP) are planning to use a "standard" smear (https://developers.google.com/time/smear https://developers.google.com/t
by joerichey 4y ago
For future leap seconds, Google (including GCP) are planning to use a "standard" smear (https://developers.google.com/time/smear https://developers.google.com/time/smear). This is also the same smear used by AWS.
It seems like if the ITU decides to keep the leap second (a bad idea, in my opinion), the large infrastructure providers will just use the same standard smear for their clocks.
- ncmncm 4y agoThey will be wrong all day long, not just for one second. AWS will be, too, evidently. Few others will do anything so idiotic.
- guipsp 4y agoThey will be wrong by at most one second. And being wrong doesn't even matter, as long as everyone (or rather, all your servers) agree.
- fanf2 4y agoAt most half a second, in the middle of the smear at midnight when the leap second is applied. The Facebook smear is asymmetrical so it starts off 1 second off just after the leap second, and subsequently corrects itself. [ The reason Google and Amazon use a linear smear is because NTP clients try to measure the rate difference between their local clock and the reference clocks; if that is different every time the NTP client queries its servers, it will have trouble locking on and accurately matching the smear curve. You can mitigate this somewhat by fixing a higher NTP query frequency, but that’s a heavy-handed fix for an engineering mistake. ]
- staticassertion 4y agoWhat are the practical issues with potentially being wrong for one day by at most one second?
- a9h74j 4y agoI assume finance and control systems to start. I might be helpful to have a fallback time-ordering algorithm not dependent upon one monotonic clock, but then you might have a rarely-used fallback to have bugs in, I imagine.
- Too 4y agoWhat are the practical issues for finance and control systems?
- denton-scratch 4y agoFor finance, it matters what order events occur in. I've never messed with control systems, but I suppose similar issues arise.
- GoblinSlayer 4y agoOrdering can be solved by a mutex.
- ncmncm 4y ago
- a9h74j 4y agoI was thinking of more distributed control systems, particularly where testing for edge cases might be difficult and rare, and rigorous methods (did Lamport solve distributed mutex?) are probably off the radar in terms of culture.
- GoblinSlayer 4y agoAny forum is a distributed system of a server and clients that agree with each other on order of user posts.
- 4y ago
- lifeisstillgood 4y agoThey are "wrong" technically but they won't be "wrong" more than a packet getting routed transatlantic would be - so if I send two packets from my laptop in London - one to AWS in London during the smear and one to another laptop in NYC, and timestamped the packets arrivals, the time stamps would likely be similar. Yes "wrong" but if it's a problem then it's a problem you have with speed of light. The answer is to find a different / reliable method of ordering.