Genuine versus Non-Genuine Atomic Multicast Protocols for Wide Area Networks: An Empirical Study

We study atomic multicast, a fundamental abstraction for building fault-tolerant systems. We suppose a system composed of data centers, or groups, that host many processes connected through high-end local links; a few groups exist, interconnected through high-latency communication links. A recent paper showed that no multicast protocol can deliver messages addressed to multiple groups in one inter-group delay and be genuine, i.e., to deliver a message m, only the addressees of m are involved in the protocol. We propose a non-genuine multicast protocol that may deliver messages addressed to multiple groups in one inter-group delay. Experimental comparisons against a latency-optimal genuine protocol show that the non-genuine protocol offers better performance in almost all considered scenarios. We also identify a convoy effect in multicast algorithms that may delay the delivery of local messages, i.e., messages addressed to a single group, by as much as the latency of global messages, i.e., messages addressed to multiple groups, and propose techniques to minimize this effect. To complete our study, we evaluate a latency-optimal protocol that tolerates disasters, i.e., group crashes.