TxChain: Scaling Sharded Decentralized Ledger via Chained Transaction Sequences

Abstract

The blockchain has become the most prevalent distributed ledger (DL). Sharding has emerged as a major solution to the scalability bottleneck of DLs. From the underlying data structure of existing sharding schemes, although the Directed Acyclic Graph (DAG)-based topology improves the scalability of DLs compared to chained blocks, the security and reliability of consensus mechanisms in DAG-based DLs have not been verified. Moreover, these schemes suffer from high communication overhead when scaling out. To address these issues, we propose a sharded DL named TxChain, which adopts a novel data structure manipulated by the unit of transaction and constituted by chained transaction sequences of each account. TxChain optimistically processes concurrent transactions and ensures the consistency of all shards via transaction sequence conversion (TSC)-based consensus mechanism. Shards maintain the full replica of TxChain and execute transactions by trustworthy validators, which reduce the frequency of communication with other shards. We theoretically prove the consistency of shards maintained by TSC and demonstrate TxChain’s throughput scales with low latency through extensive experiments.