Nexus: Efficient and Conflict-Equivalent DAG-Based Permissioned Blockchain Sharding

Sharding is one of the most promising solutions to tackle the well-known scalability issue in blockchain by dividing the network into multiple parallel committees. However, inefficient and insecure handling of cross-shard transactions can lead to a decline in the system service quality. Existing permissioned blockchains are mainly based on the classic two-phase commit (2PC) and two-phase locking (2PL) from traditional distributed databases to implement cross-shard transactions with deterministic safety, but this also leads to issues such as decreased system throughput and frequent transaction aborts. In this paper, we introduce Nexus, an efficient and conflict-equivalent sharded permissioned blockchains to overcome the aforementioned challenges. The core idea of Nexus is to construct a directed acyclic graph (DAG) among all shards to establish a partial order of blocks, while leaving transaction dissemination and final ordering to be completed in parallel by each shard. Nexus alleviate the overhead of global ordering through a efficient consensus process, and ensure that all transactions with overlapping read and write sets can be committed in the same relative order across different shards. A prototype of Nexus is implemented and evaluated, and experimental results show that Nexus achieves approximately 70% and 50% throughput improvement over AHL and SharPer under default settings.