Quoting Jonathan S. Shapiro (shap@eros-os.org):
> What's the granularity? I want better than seconds. It's not that I think
> the clocks are accurate, but more bits tends to avoid sort collisions even
> when they are bad bits.
>
I would try to have granularity of at least nanoseconds. The FreeBSD stat command returns nanosecond granularity for ctime, atime, and mtime. A 64bit counter is good at this granularity for about 580 years. Maybe you want to avoid the Y2.5K problem, maybe you don't. I would prefer storing a string representation of the number of nanoseconds since the epoch and using 64bits for internal computation.
-josh