Poul-Henning Kamp
Abstract
Finding a lasting solution to the leap seconds problem has become increasingly urgent.
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Index Terms
- The one-second war
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Reviews
Giuseppina Carla Gini
"What time is it__?__" When we answer this trivial question, we don't care about seconds. However, as computer scientists, we should. The length of a second is astronomically defined in terms of the earth's rotation, and practically defined in the International System of Units (SI) in terms of periods of hyperfine radiation from cesium-133 atoms. Since there are small variations in the earth's rotation, the length of a second varies, and should be periodically determined. As a result, the decision to use SI seconds and do full-second step adjustments (leap seconds) started on January 1, 1972. In practice, twice a year, astronomers can determine whether the last minute of June and of December will consist of 59, 60, or 61 seconds. Why care about this adjustment__?__ The advent of large synchronized networks of computers requires that they are always aligned in time. Different systems managed the leap seconds in different ways. In practice, many of the network time protocol (NTP) servers had this one-second difference for a short time, both in 2005 and 2008, when the last leap seconds arrived. The problem is that many systems besides computers care about time, including air traffic control (ATC) systems and many industrial processing systems that are time critical. How can we be sure that all computers know about leap seconds and fix the code on time__?__ According to Kamp, nobody knows. The most-used solution is to maintain all of the critical systems for some time to cover the leap second. This is a waste of time and money. Why not abolish them__?__ Kamp advances another solution: if it were possible to know 20 years in advance when leap seconds were due, it would be easier to maintain them by simply adding the right number of seconds for every day into any program. But, he argues, are all programmers really able to do that__?__ Furthermore, don't more important problems exist__?__ Waiting to see if the proposal to abolish leap seconds will be accepted in January 2012, we can only agree with the practical considerations raised by the author. As scientists, however, we should consider a longer time horizon and broader reasons for our decisions. Online Computing Reviews Service
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