Effect of earth’s rotation on IIS logs
I was amazed when I observed “UTC” time tag associated with IIS logs. In this blog post, I would be explaining what UTC time is, how it is different from GMT, how it is been used in IIS logs and the difference it makes. Being physics enthusiastic, it was fascinating to know how geographical physics is rooted within our computer systems. I was under the belief that GMT (Greenwich Mean Time) is the standard accepted in internet and computer networks. However, that’s not true.
The accepted standard for Internet protocols used in many WWW applications is UTC but not GMT. UTC stands for Coordinated Universal Time. Even though, there isn’t much difference between GMT and UTC, however UTC is far more accurate compared to GMT. UTC time standard is based on atomic time units with leap seconds added at irregular time intervals. It has been calculated that Earth’s rotation is slowing down by margin of 2 milliseconds a day, hence increasing the day time to 86,400.002 seconds. 2 milliseconds overhead each day sums up to 1 second after around 18 months. Hence, in UTC standard, one extra leap second is added once 1 second overhead is accumulated. Certain research papers have indicated that there might be acceleration in earth’s rotation due to movements in earth’s crust. However, the margin of deceleration is higher than acceleration; hence the more and more leap seconds will get inserted in the coming years.
One of the internet standard that uses UTC time format for logging is W3C standard. (http://www.w3.org/TR/NOTE-datetime). W3C logging standard is being used in Internet Information Services (IIS). If you enable the IIS logs, then the time field you see is in UTC format. Occasionally, if you see 1 second leaps in it compared to your clock, then it’s due to UTC time format. However, these leaps happen once in 18 months and you should be really lucky to notice it.
Having read all that, if must be wondering, what’s so interesting in this? All I am trying to convey is that how much care we are taking making our data accurate. The technologists involved in making this happen should be applauded for their extra effort in perfecting the system.