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June 30th Leap Second Could Trigger Unexpected Issues
dkatana writes: On January 31, 2013, approximately 400 milliseconds before the official release of the EIA Natural Gas Report, trading activity exploded in Natural Gas Futures. It is believed that was the result of some fast computer trading systems being programmed to act, and have a one-second advance access to the report. On June 30th a leap second will be added to the Network Time Protocol (NTP) to keep it synchronized with the slowly lengthening solar day. In this article, Charles Babcock gives a detailed account of the issues, and some disturbing possibilities: The last time a second needed to be added to the day was on June 30, 2012. For Qantas Airlines in Australia, it was a memorable event. Its systems, including flight reservations, went down for two hours as internal system clocks fell out of synch with external clocks.
The original author of the NTP protocol, Prof. David Mills at the University of Delaware, set a direct and simple way to add the second: Count the last second of June 30 twice, using a special notation on the second count for the record. Google will use a different approach: Over a 20-hour period on June 30, Google will add a couple of milliseconds to each of its NTP servers' updates. By the end of the day, a full second has been added. As the NTP protocol and Google timekeepers enter the first second of July, their methods may differ, but they both agree on the time.
But that could also be problematic. In adding a second to its NTP servers in 2005, Google ran into timekeeping problems on some of its widely distributed systems. The Mills sleight-of-hand was confusing to some of its clusters, as they fell out of synch with NTP time. Does Google's smear approach make more sense to you, or does Mills's idea of counting the last second twice work better? Do you have a better idea of how to handle this?
The original author of the NTP protocol, Prof. David Mills at the University of Delaware, set a direct and simple way to add the second: Count the last second of June 30 twice, using a special notation on the second count for the record. Google will use a different approach: Over a 20-hour period on June 30, Google will add a couple of milliseconds to each of its NTP servers' updates. By the end of the day, a full second has been added. As the NTP protocol and Google timekeepers enter the first second of July, their methods may differ, but they both agree on the time.
But that could also be problematic. In adding a second to its NTP servers in 2005, Google ran into timekeeping problems on some of its widely distributed systems. The Mills sleight-of-hand was confusing to some of its clusters, as they fell out of synch with NTP time. Does Google's smear approach make more sense to you, or does Mills's idea of counting the last second twice work better? Do you have a better idea of how to handle this?
Typically when dealing with NTP you do not want big swings. In fact, a system using NTP that's too far out of sync, won't sync back up correctly. One that is slightly out of sync will slowly come back in sync over a period of time, hours or days even. Both approaches could work, they really could, but I think adding a few milliseconds here and there is a better way to get this done as long as the systems don't fall too far behind. I work with Avaya voice equipment and we've been warning people about this for months and months. We've provided instructions on several methods to ensure this doesn't cripple your system, but it all depends on how your NTP is setup. I also foresee issues with just adding an extra second to the day, this is not going to work for a bunch of systems and will actually throw them out of sync compared to googles approach. One of the solutions we've "provided" is to disable NTP shortly before the time roll over, then enable it once it's July. That's a pain in the butt, but if you can afford the few minutes of service interruption, it solves all of the issues right there, you turn it off when it's synced, turn it back on and it syncs to the new time. The real issues come in, for my field at least, with logging, this is going to throw a wrench into sys logs if it's not taken care of, and with some of the platforms, it will literally cripple the system.
I'm willing to accept that layouts change and I'll need to look in a new place--but the new location is actually terrible usability. Here's why:
First, I read the headline. Then, I read the summary. I'm moving down the page, and I'm scrolling the page, too. So, now I'm at the end of the summary, and the headline for any story with a long summary is now out of the window. Now, I need to scroll back up to see how many comments or to click to view those comments. Extra work, even if the summary isn't long.
Fitts' Law applies here. They've made the target smaller in diameter, and placed it further away effectively. That means the difficulty of clicking to view comments is noticeably harder.