Tom Van Baak wrote:
Keep in mind that this system drives you to having pretty bad time for the
better part of a whole day, on purpose... I realize that when the
Hi Didier,
The google article never claims the smear spans an entire day. I
think you may be confusing references to the leap smear with a DIY
digital clock someone on the list wanted to build (and they proposed
using a slow 86400 second slew).
The google code is "lie(t) = (1.0 - cos(pi * t / w)) / 2.0" and they
are wise not to publish the actual window value, w. If it were me I'd
make it somewhere between a couple of seconds or couple of minutes
but I too would not make it a published or hardcoded constant.
Hm, the article says, "It also made sure the updates were sufficiently
small so that any software running on the servers that were doing
synchronization actions or had Chubby locks wouldn't lose those locks or
abandon any operations."
So I think they smeared it over more than just a few minutes. I'd expect
some hours, so standard NTP clients would just notify this as clock
drift (oscillator frequency offset) which they'd have to compensate.
Since ntpd's control loop is pretty slow it wouldn't respond quickly to
smears over a few seconds our hours.
Here's the link again:
http://googleblog.blogspot.com/2011/09/time-technology-and-leaping-seconds.html
Again, I don't know what value they use, or even if they use the same
value from one leap second to the next. If any of you have inside
contacts with google and can find out let me know, off-list.
>
Regardless, it should be possible to experimentally determine the
smear duration by repeatedly using some google service that returns
time-stamps during the day, hours, minutes, or seconds before and
after June 30. It would make a nice posting for a time nut, or a
research paper for a high school student or undergrad: Experimental
Confirmation of Google's Leap Smear Algorithm.
Yes, interesting idea!
Martin
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