I was pleased when I read the spanner paper to see that they had gone to locally authoritative stratum 0 clocks. I long time ago in a different universe it seems, I struggled with the notions of replcated naming logs which needed to converge to a common and consistent results. It wasn't until I got to play with the combinator technology at Blekko did I feel like there was a good answer to the problem. Clouds of idempotent expressions of execution don't need clocks at all, if you have them all, you have your answer. That was a neat result.