The internet skips a beat

Following the difficulties encountered with various computer systems after the introduction of a leap second this morning, an interesting post describing how Google add an extra second to the day without introducing a clock jump:

Computers traditionally accommodate leap seconds by setting their clock backwards by one second at the very end of the day. But this “repeated” second can be a problem. For example, what happens to write operations that happen during that second? ...

The solution we came up with came to be known as the “leap smear.” We modified our internal NTP servers to gradually add a couple of milliseconds to every update, varying over a time window before the moment when the leap second actually happens. This meant that when it became time to add an extra second at midnight, our clocks had already taken this into account, by skewing the time over the course of the day.

And even more apposite now than it was when it was written, Falsehoods programmers believe about time.