  Online applications now routinely replicate their data at multiple sites
around the world. In this paper we present Atlas, the first state-machine
replication protocol tailored for such planet-scale systems. Atlas does not
rely on a distinguished leader, so clients enjoy the same quality of service
independently of their geographical locations. Furthermore, client-perceived
latency improves as we add sites closer to clients. To achieve this, Atlas
minimizes the size of its quorums using an observation that concurrent data
center failures are rare. It also processes a high percentage of accesses in a
single round trip, even when these conflict. We experimentally demonstrate that
Atlas consistently outperforms state-of-the-art protocols in planet-scale
scenarios. In particular, Atlas is up to two times faster than Flexible Paxos
with identical failure assumptions, and more than doubles the performance of
Egalitarian Paxos in the YCSB benchmark.
