Despite recent progresses of practical asynchronous Byzantine fault tolerant (BFT) consensus, the state-of-the-art designs still suffer from suboptimal performance. Particularly, to obtain maximum throughput, most existing protocols with guaranteed linear amortized communication complexity require each participating node to broadcast a huge batch of transactions, which dramatically sacrifices latency. Worse still, the f slowest nodes' broadcasts might never be agreed to output and thus can be censored (where f is the number of faults). Implementable mitigation to the threat either uses computationally costly threshold encryption or incurs communication blow-up, thus causing further efficiency issues. We present Dumbo-NG, a novel asynchronous BFT consensus (atomic broadcast) to solve the remaining practical issues. Its technical core is a non-trivial direct reduction from asynchronous atomic broadcast to multi-valued validated Byzantine agreement (MVBA) with quality property. Most interestingly, the new protocol structure empowers completely concurrent execution of transaction dissemination and asynchronous agreement. This brings about two benefits: (i) the throughput-latency tension is resolved to approach peak throughput with minimal increase in latency; (ii) the transactions broadcasted by any honest node can be agreed to output, thus conquering the censorship threat with no extra cost. We implement Dumbo-NG and compare it to the state-of-the-art asynchronous BFT with guaranteed censorship resilience including Dumbo (CCS'20) and Speeding-Dumbo (NDSS'22). We also apply the techniques from Speeding-Dumbo to DispersedLedger (NSDI'22) and obtain an improved variant of DispersedLedger called sDumbo-DL for comprehensive comparison. Extensive experiments reveal: Dumbo-NG realizes better peak throughput performance and its latency can almost remain stable when throughput grows.

翻译：尽管近年来实用的异步拜占庭容错（BFT）共识取得了进展，但最先进的设计仍存在性能欠佳的问题。具体而言，为了获得最大吞吐量，现有大多数保证线性平摊通信复杂度的协议要求每个参与节点广播大量交易批次，这显著牺牲了延迟。更严重的是，最慢的f个节点的广播可能永远无法达成输出共识，从而可能被审查（其中f表示故障节点数）。针对该威胁的可实现缓解方案要么使用计算成本高昂的阈值加密，要么导致通信开销激增，进而引发进一步的效率问题。本文提出Dumbo-NG，一种新型异步BFT共识（原子广播）以解决上述实用化难题。其技术核心是从异步原子广播到具有质量属性的多值有效拜占庭协议（MVBA）的非平凡直接约简。最有趣的是，新型协议结构实现了交易分发与异步共识的完全并发执行，由此带来两大优势：（i）吞吐量-延迟矛盾得以化解，可在延迟最小化增长的情况下逼近峰值吞吐量；（ii）任意诚实节点广播的交易均可达成输出共识，从而无需额外成本即可抵御审查威胁。我们实现了Dumbo-NG，并将其与当前最先进的具有审查抵御能力的异步BFT协议（包括Dumbo（CCS'20）和Speeding-Dumbo（NDSS'22））进行对比。同时，我们将Speeding-Dumbo的技术应用于DispersedLedger（NSDI'22），得到其改进变体sDumbo-DL以进行综合比较。大量实验表明：Dumbo-NG实现了更优的峰值吞吐性能，且其延迟在吞吐量增长时几乎保持稳定。