Byz-GentleRain: An Efficient Byzantine-tolerant Causal Consistency Protocol

TL;DR

Byz-GentleRain is a novel Byzantine-tolerant causal consistency protocol that ensures data consistency in distributed systems with Byzantine faults, using PBFT for agreement and achieving efficiency in practical workloads.

Contribution

It introduces the first causal consistency protocol that tolerates Byzantine faults among servers and clients, extending prior work limited to non-Byzantine clients.

Findings

Achieves causal consistency with Byzantine fault tolerance.

Uses PBFT for agreement on global stable times.

Demonstrates efficiency on typical workloads.

Abstract

Causal consistency is a widely used weak consistency model that allows high availability despite network partitions. There are plenty of research prototypes and industrial deployments of causally consistent distributed systems. However, as far as we know, none of them consider Byzantine faults, except Byz-RCM proposed by Tseng et al. Byz-RCM achieves causal consistency in the client-server model with $3f + 1$ servers where up to $f$ servers may suffer Byzantine faults, but assumes that clients are non-Byzantine. In this work, we present Byz-Gentlerain, the first causal consistency protocol which tolerates up to $f$ Byzantine servers among $3f + 1$ servers in each partition and any number of Byzantine clients. Byz-GentleRain is inspired by the stabilization mechanism of GentleRain for causal consistency. To prevent causal violations due to Byzantine faults, Byz-GentleRain relies on PBFT to reach agreement on a sequence of global stable times and updates among servers, and only updates with timestamps less than or equal to such common global stable times are visible to clients. We prove that Byz-GentleRain achieves Byz-CC, the causal consistency variant in the presence of Byzantine faults. We evaluate Byz-GentleRain on Aliyun. The preliminary results show that Byz-GentleRain is efficient on typical workloads.