The previous leap second in 2012 caused some popular online systems to crash and grounded flights in Australia
Technology and finance organisations are preparing for a “leap second” to be introduced to Coordinated Universal Time (UTC) at midnight on Tuesday, learning lessons from the disruption to electronic and online systems caused by 2012’s time correction.
This year’s leap second is the first since markets went electronic to be introduced during trading hours, and some financial organisations said they would be suspending trading in order to avoid disruption.
A leap second is a correction introduced to highly precise timekeeping systems, such as atomic clocks, that’s necessary to keep them in line with solar time – that is, time as it is indicated by where the sun stands in the sky.
The earth’s rotation is gradually slowing due to factors such as the gravitational drag of the moon, meaning that without leap seconds, atomic clocks would gradually drift out of line with solar time.
Over the course of about 800 years uncorrected clocks would indicate 1pm, instead of noon, when the sun was at its highest point in the sky. Timekeepers have added leap seconds into UTC since 1972 – this year’s is the 27th.
Most computer systems are, however, not built to handle shifts in their timekeeping systems. 2012’s leap second, introduced on a weekend, crashed Mozilla, Gawker, Reddit and LinkedIn and grounded more than 400 flights in Australia as the Qantas check-in system went down. Problems with Linux and Java were also reported.
The National Physical Laboratory (NPL), responsible for defining Greenwich Mean Time, said problems could be caused if some systems apply the leap second in a different way or at a slightly different time.
Google’s time ‘smear’
UTC, which is defined by the UN’s International Telecommunications Union (ITU), will officially apply the second at midnight with a 61-second minute, but other organisations have announced other plans for implementing it.
Google said it is to use a custom system that will slightly slow down all of its servers’ clocks during a period of 20 hours.
“Instead of repeating a second, we ‘smear’ away the extra second. During a 20-hour ‘smear window’ centered on the leap second, we slightly slow all our servers’ system clocks,” Google said in a blog post. “At the end of the smear window, the entire leap second has been added, and we are back in sync with civil time.”
Google said the technique makes the second “invisible” to get around the fact that its software isn’t written to be able to adjust to leap seconds, and introduced the technique based on its experiences with 2005’s leap second.
“Most software isn’t written to explicitly handle leap seconds, including most of ours,” Google said. “During the 2005 leap second, we noticed various problems like this with our internal systems.”
Amazon Web Services said last month it planned to implement a similar technique.
Nasdaq said it plans to shut down after-hours trading half an hour early to avoid problems that might be caused by the leap second, while the Intercontinental Exchange (ICE) said it would delay its commodity trading markets’ opening to mitigate problems.
“ICE is confident that this will not cause any issues on our systems; however, we cannot guarantee the same for all systems used by our participants, market data vendors, and other third-parties,” ICE stated. “As a result, ICE has made the decision to delay all market state transitions which would normally occur between June 30th 23.00 GMT and July 1st 00.01 GMT.”
Several countries, including the US and France, are arguing leap seconds should be abolished due to their disruptive effect on computer systems, meaning civil time would no longer be synchronised with “Universal Time”, the principal timekeeping standard based on solar time.
Others, including Britain, Russia and China argue that the effects of leap seconds are manageable. The ITU is set to reach a decision on the matter in November.
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