[LEAPSECS] Google, Amazon, now Microsoft

Poul-Henning Kamp phk at phk.freebsd.dk
Mon Jun 1 02:46:58 EDT 2015

In message <556BFD47.4050501 at edlmax.com>, Brooks Harris writes:

>>Multiply this by 250 million [1] PC's still happily running XP
>>and you can better understand why Microsoft hasn't been that
>>interested in leap seconds, NTP, or participating in the hh:59:60
>>timestamp nightmare.

>Yes, they've got a very large number of badly administrated systems in 
>the field. In more tightly administrated systems it can be done better. 
>But its all "good enough" for current purposes.

That's not as obvious as you seem to think.

A lot of Windows machines are doing things where you would expect
people to care about leap-seconds:  Nuclear power plants control
systems, Air Traffic Control computers, Surgery robots, Patient
Monitors, Power grid disturbance detectors etc.  etc. etc.

Fact is that most of the people involved in these systems have no idea
what a leap-second is, and more crucially:  Once they learn that, they
have no idea what the system they designed will do when one happens.

>> It would make sense, like Google and Amazon, that their in-house
>> data centers would want to more precisely and deterministically
>> handle leap seconds. But note all three companies have decided to
>> jump or smear time instead of creating a true leap second.

>As I understand it its not that they are interested in "precise" or 
>"accurate" time - they are interested in smoothing over the Leap Second 
>to avoid problems potentially caused by the Leap Second jump in the many 
>OSs running in the data centers.

They are very much interested in both *precise* and *accurate* time,
that's why they have to do something in the first place.

If they were not interested in good timekeeping, they could just
let the computers free-run their clocks and pretend this is the 1980ies.

And yes, the smoothing and ramping and steps are all attempts to
win predictability at the expense of accuracy, when faced with at
huge amount of software written by the kind of people mentioned above.

But this is not something they are happy about doing, much less
proud of doing, but weighing the risks of "heterogeneous" leap-second
handling and the risk of being up to half a second wrong about time
for most of a day, they picked the second risk.

Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.

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