Bolt-Dumbo Transformer: Asynchronous Consensus As Fast As Pipelined BFT

Optimistic asynchronous atomic broadcast (Kursawe and Shoup, 2002; Ramasamy and Cachin, 2005) has been proposed to leverage the "hybridization" art to improve the performance of asynchronous protocols while remaining their robust liveness against unstable network. The basic idea is to run faster deterministic protocols in the optimistic case when network condition is good, while safely fallback to a pessimistic path running asynchronous protocols when the protocol fails to proceed. Unfortunately, the existing fallback mechanisms directly use a heavy tool of multivalued asynchronous validated Byzantine agreement (MVBA). The resulting fallback mechanisms would become even less efficient than the underlying asynchronous protocol. When network is fluctuating, the benefit of adding the deterministic protocol for the optimistic case will be directly eliminated since the inefficient fallback may happen frequently. We present a new generic framework for practical optimistic asynchronous atomic broadcast. In particular, we give a new abstraction of the optimistic case protocol, which prepared us to design a highly efficient fallback mechanism, and can be instantiated easily. The latter not only reduces the communication complexity by a factor of $\mathcal{O}(n)$, but also replace the cumbersome MVBA protocol with a type of binary agreement only. We give a detailed security analysis and also instantiate our framework with doing extensive real-world experiments to show the minimal overhead of our fallback mechanism.