PrimCast: A Latency-Efficient Atomic Multicast

Atomic multicast is a communication abstraction that allows for messages to be addressed to and reliably delivered by multiple process groups, while ensuring a partial order on delivered messages. Strong ordering guarantees can greatly simplify the design and implementation of distributed applications. One critical property for the performance and scalability of an atomic multicast protocol is that of genuineness: a protocol is said to be genuine if only the sender and destinations of a message are involved in ordering the message. This paper presents PrimCast, the first genuine atomic multicast protocol able to deliver messages at every destination in three communication steps. PrimCast uses a primary-based consensus protocol for deciding on message timestamps at each group. Differently from previous work, it does not rely on consensus for advancing and maintaining logical clocks. PrimCast introduces a novel approach, relying on simple quorum intersection, to decide when a multicast message can be delivered. We also show how loosely synchronized clocks can be used to reduce the convoy effect that delays messages under high system load. We present the complete algorithm for PrimCast and evaluate its performance under various scenarios. Our results show that PrimCast achieves lower latency than state-of-the-art approaches while providing higher or comparable throughput.