PnyxDB: a Lightweight Leaderless Democratic Byzantine Fault Tolerant Replicated Datastore

Byzantine-Fault-Tolerant (BFT) systems for closed consortia have recently attracted a growing attention notably in financial and supply-chain applications. Unfortunately, most existing solutions suffer from substantial scalability issues, and lack self-governance mechanisms. In this paper, we observe that many workloads present little concurrency, and propose PnyxDB, an eventually-consistent Byzantine Fault Tolerant replicated data-store that exhibits both high scalability and low latency. Our approach hinges on conditional endorsements that track conflicts between transactions. In addition to its high scalability, PnyxDB supports application-level voting, i.e. individual nodes are able to endorse or reject a transaction according to application-defined policies without compromising consistency. We provide a comparison against BFT-SMART and Tendermint, two competitors with different design aims, and show that our implementation speeds up commit latencies by a factor of 11, remaining below 5 seconds in a worldwide geodistributed deployment of 180 nodes.