Conflict-free Quorum-based BFT Protocols

Quorum-based Byzantine fault-tolerant protocols for replicated state machines allow replicas to respond to client requests without explicitly agreeing on the request ordering. As long as concurrent write operations do not conflict, quorum-based protocols are more efficient than agreement-based protocols. However, resolving conflicting writes and bringing replicas up-to-date with each other is a principal performance limitation of existing quorum protocols. We present a simple technique based on an un-trusted pre-serializer to completely mask such quorum-based BFT protocols from experiencing conflicting writes. Experimental results show that a non-faulty pre-serializer enables such quorum protocols to retain their efficiency even under significant write contention.