Genuine versus Non-Genuine Atomic Multicast Protocols

In this paper, 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. In this context, a recent paper has shown 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 first survey and analytically compare existing multicast algorithms to identify latency-optimal multicast algorithms. We then 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 all considered scenarios, except in large and highly loaded systems. To complete our study, we also evaluate a latency-optimal protocol that tolerates disasters, i.e., group crashes.