time - Why Does the Leap Second Cause Problems?

Question

So at this moment (but most likely not for long) Reddit, Meetup, Fark, LinkedIn, Yelp, 4Chan are all down. Netflix apparently was out for a while too.

According to Reddit's tweet, they are having issues relating to the Leap Second from 6/30/2012: https://twitter.com/redditstatus/status/219244389044731904

"We are having some Java/Cassandra issues related to the leap second at 5pm PST. We're working as quickly as we can to restore service."

Apparently, the issues affecting the other sites are all related to a leap second issue.

After reading Wikipedia article on Leap seconds, I think I understand what leap seconds are... but what I don't get is what kind of weird behaviors can happen if leap second isn't accounted for? And how, as programmers, should we prepare for leap seconds when we code and configure servers?

I mean it's only one second isn't it?

Answer 1

Certain Linux kernels (versions before 2.6.29) have issues handling leap seconds, to the point where it can cause a kernel panic. Other Linux kernels can suffer from a livelock. This obviously has detrimental effects for the system, given that it requires a reboot.

Here's the related ServerFault question on this topic, since it's really a Linux server issue.