HQ Replication: A Hybrid Quorum Protocol for Byzantine Fault Tolerance

There are currently two approaches to providing Byzantine-fault-tolerant state machine replication: a replica-based approach, e.g., BFT, that uses communication between replicas to agree on a proposed ordering of requests, and a quorum-based approach, such as Q/U, in which clients contact replicas directly to optimistically execute operations. Both approaches have shortcomings: the quadratic cost of inter-replica communication is unnecessary when there is no contention, and Q/U requires a large number of replicas and performs poorly under contention. We present HQ, a hybrid Byzantine-fault-tolerant state machine replication protocol that overcomes these problems. HQ employs a lightweight quorum-based protocol when there is no contention, but uses BFT to resolve contention when it arises. Furthermore, HQ uses only 3f +1 replicas to tolerate f faults, providing optimal resilience to node failures. We implemented a prototype of HQ, and we compare its performance to BFT and Q/U analytical...

• Type: Conference
• Year: 2006
• Where: OSDI
• Authors: James A. Cowling, Daniel S. Myers, Barbara Liskov, Rodrigo Rodrigues, Liuba Shrira
• Keywords: Byzantine-fault-tolerant State Machine, Lightweight Quorum-based Protocol, Operating System, OSDI 2006, State Machine Replication