OverShard: Scaling blockchain by full sharding with overlapping network and virtual accounts

Abstract

One of the primary challenges to the widespread adoption of blockchain technology is scalability. Although sharding is considered one of the most promising solutions, it still struggles to process cross-shard transactions adequately. In this paper, we propose OverShard, a full sharding approach for scaling blockchain that incorporates an overlapping network and virtual accounts. The overlapping network model enables all nodes in a shard to join multiple other shards, thereby enhancing security in a sharded system and improving communication efficiency between nodes in different shards. Moreover, the virtual accounts model facilitates transaction processing within a single shard. To the best of our knowledge, OverShard is the first model to fully address the issue of cross-shard transactions, theoretically leading to almost linear scalability with an increasing number of shards. Additionally, OverShard supports both transfer transactions and smart contract transactions in permissionless blockchain systems. We provide an analysis of the security, scalability, and performance of OverShard, then implement a prototype system of 1200 nodes with 128 shards, each joining 12 shards. Although each node's storage and communication overhead increases compared to a traditional sharding network, OverShard can scale up to nearly 128× the throughput (equal to the number of shards), with confirmation latency remaining at only one block interval.