[haberman]

The question of how to reconcile leap-second-smearing systems with other systems is an interesting and important one. I'm not sure that timestamp.proto changes this issue: prior to timestamp.proto systems would still communicate using UNIX time (smeared or non-smeared) using plain integer or double seconds. timestamp.proto just provides a structure for storing UNIX time with greater range and precision than a single integer or floating point number can provide.

What I'm trying to say is that I think this is a smearing systems vs. non-smearing systems issue, and not so much a timestamp.proto issue. timestamp.proto mentions smearing but really it's just a vehicle for storing the seconds/nanos from the system clock, with whatever semantics that system clock uses. Because in practice systems don't give you access to both the smeared and non-smeared values; you get whatever the system gives you. The remarks about being leap-second-ignorant apply whether the leap second is being smeared or repeated.

Google implemented leap-second smearing in 2011, before the big push towards cloud. So the need to communicate sub-second timestamps between internal Google systems and external systems was probably not so much on people's minds. But these days we're releasing a bunch of APIs, and sub-second timestamps might become a more important issue for some of them.

So I think this issue is worth discussing further, and I opened an issue on GitHub to track it: https://github.com/google/protobuf/issues/1890

Thanks for the feedback.