Sharding enhances blockchain scalability by partitioning nodes into multiple groups for concurrent transaction processing. Configuring a large number of \emph{small shards} helps improve the transaction concurrency of a sharding system. However, it increases the fraction of malicious nodes within each shard, easily leading to shard corruption and jeopardizing system security. Some existing works have attempted to improve concurrency by reducing the shard size while maintaining security. However, they often require frequent and time-consuming recovery of corrupted shards, leading to severe system stagnation. Also, they usually require network-wide consensus to guarantee security, which limits scalability. To address these issues, we propose DL-Chain, a blockchain sharding system that can securely provide \emph{high concurrency with stable and scalable performance.} Our core idea is a \underline{D}ual-\underline{L}ayer architecture and consensus, which consists of numerous smaller proposer shards (PSs) for transaction processing and multiple larger finalizer committees (FCs) for transaction finalization. To avoid system stagnation and thus guarantee stable performance, we ensure PSs' liveness even if they are corrupted through the cooperation of PSs and FCs, thus eliminating the recovery process of corrupted PSs. To better trade-off security and scalability, we fine-tune the FCs to enable multiple FCs to coexist securely. As a result, DL-Chain allows a larger fraction of malicious nodes in each PS ($<1/2$) and thus can securely configure smaller shards for boosted stable and scalable concurrency. Evaluation results show that DL-Chain achieves up to 10 times improvement in throughput compared to existing solutions and provides stable concurrency with up to 2,550 nodes.

翻译：分片技术通过将节点划分为多个组以实现并发交易处理，从而提升区块链的可扩展性。配置大量\emph{小型分片}有助于提高分片系统的交易并发性。然而，这也会增加每个分片内恶意节点的比例，容易导致分片腐化并危及系统安全。现有的一些研究尝试通过缩小分片规模同时保持安全性来提高并发性，但这些方案通常需要频繁且耗时的腐化分片恢复过程，导致严重的系统停滞。此外，它们通常需要全网共识来保证安全性，这限制了可扩展性。为解决这些问题，我们提出了DL-Chain，一种能够安全提供\emph{高并发性且具备稳定、可扩展性能}的区块链分片系统。我们的核心思想是采用\underline{双}层\underline{架}构与共识机制，该机制由大量较小的提案者分片（PS）负责交易处理，以及多个较大的最终确认委员会（FC）负责交易最终确认。为避免系统停滞从而保证稳定性能，我们通过PS与FC的协作确保PS即使在腐化状态下仍能保持活性，从而消除了腐化PS的恢复过程。为更好地权衡安全性与可扩展性，我们对FC进行精细调优，使多个FC能够安全共存。因此，DL-Chain允许每个PS中存在更高比例的恶意节点（$<1/2$），从而能够安全配置更小的分片以提升稳定且可扩展的并发性。评估结果表明，与现有方案相比，DL-Chain的吞吐量最高可提升10倍，并在多达2,550个节点的规模下提供稳定的并发性能。