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Yes. Leap seconds are just a thoroughly bad idea, from any angle. Yet, not nearly so bad as Google's approach: no leap, but a 24-hour smear, during which 24 ho
by ncmncm 4y ago
Yes. Leap seconds are just a thoroughly bad idea, from any angle.
Yet, not nearly so bad as Google's approach: no leap, but a 24-hour smear, during which 24 hours they are out of sync with literally everybody else in the world.
- joerichey 4y agoFor 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.
- 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.
- mattnewton 4y agoDidn’t Google change their smear to 24 hours because it was what AWS and some other internet time servers used?
- ncmncm 4y agoYes: which shows that the skew was a problem. Eliminate UTC leap seconds, and the overwhelmingly worse smear problem vanishes too.
- deleted 4y ago[deleted]
- oittaa 4y agoAWS does exactly the same. > The AWS Management Console and backend systems will NOT implement the leap second. Instead, we will spread the one extra second over a 24-hour period surrounding the leap second by making each second slightly longer. https://aws.amazon.com/blogs/aws/look-before-you-leap-the-coming-leap-second-and-aws/ https://aws.amazon.com/blogs/aws/look-before-you-leap-the-co...
- ncmncm 4y agoI.e., be out of sync all day long with literally everybody except Google.
- zsims 4y agoAt that point, how much of the internet is that?
- ncmncm 4y agoAlmost everybody. AWS and Google would like to think the internet is just them, but they are a tiny little bit of it.
- nvr219 4y agoNo, you don't understand, Amazon and Google will be right, and everyone else will be out of sync with THEM.
- Gigachad 4y agoWhat is the consequence of being a fraction of a second out of sync?
- londons_explore 4y agoAlgorithms that involve 'i did this thing at this time, everyone else should wait for that time to have passed before continuing to ensure correct ordering' (ie. Many database systems) will dramatically slow down. Systems that use atomic clocks might have been able to do 10,000 transactions per second will suddenly only be able to do 2 transactions per second if they contain a node that doesn't use the same smearing.
- deleted 4y ago[deleted]
- Thorrez 4y agoMeta also smears, as mentioned in the article. The article calls smearing "common practice". I think smearing can help reduce outages. The article mentions that reddit and Cloudlare had outages caused by leap seconds when they weren't smearing. I think it's a tradeoff between being standard and avoiding outages. Disclosure, I work at Google.