GeoChain: A Locality-Based Sharding Protocol for Permissioned Blockchains

Blockchain is a distributed ledger that uses cryptography and consensus protocols to record a growing list of transactions in a tamper-resistant manner. Scalability is one of the main problems that limit its usage. This paper introduces a full sharding protocol, Geochain, for permissioned blockchains. We first clarify the limitations of state-of-the-art sharding protocols. Then, we propose a locality-based sharding protocol that achieves high scalability. We optimize inter-shard performance by clustering participants using their geographical properties, locality. In addition, the locality is also employed to decide the transaction placement which results in a low ratio of cross-shard transactions for applications, such as everyday banking, retail payments, and electric vehicle charging. We also propose a client-driven efficient mechanism to handle cross-shard transactions and present an analysis. This enables clients to manage their assets across different shards directly. A prototype is implemented on top of Hyperledger Fabric v2.3 and evaluated on Amazon EC2. The experiments show that our protocol doubles the peak throughput, even with a high ratio of cross-shard transactions, while minimizing the transaction latency.