Abraxas: Throughput-Efficient Hybrid Asynchronous Consensus

Protocols for state-machine replication (SMR) often trade off performance for resilience to network delay. In particular, protocols for asynchronous SMR tolerate arbitrary network delay but sacrifice throughput/latency when the network is fast, while partially synchronous protocols have good performance in a fast network but fail to make progress if the network experiences high delay. Existing hybrid protocols are resilient to arbitrary network delay and have good performance when the network is fast, but suffer from high overhead (''thrashing'') if the network repeatedly switches between being fast and slow, e.g., in a network that is typically fast but has intermittent message delays. We propose Abraxas, a generic approach for constructing a hybrid protocol from any ''fast'' protocol Πfast and asynchronous protocolΠslow to achieve (1) security and performance equivalent to Πslow under arbitrary network behavior, and (2) performance equivalent to Πfast when conditions are favorable. We instantiate Abraxas with the best existing protocols for Πfast (Jolteon) and Πslow (\mbox2-chain VABA), and show experimentally that the resulting protocol significantly outperforms Ditto, the previous state-of-the-art hybrid protocol.