LB-Chain: Load-Balanced and Low-Latency Blockchain Sharding via Account Migration

Blockchain sharding has been increasingly used to improve blockchain systems' performance, in which a blockchain is split into multiple smaller, disjoint shards. In practice, however, sharding can only achieve limited throughput and latency improvement, especially for the user-perceived transaction confirmation delay. The performance degradation is believed to be caused by the cross-shard transactions. However, we show, through comprehensive system deployment and measurement studies, that the main culprit is the imbalanced transaction load on different blockchain shards. To address this problem, we propose a novel sharding system, called LB-Chain, which dynamically balances the transaction load on different shards by periodically migrating active accounts from heavily-loaded shards to less-loaded ones. We have implemented a prototype of LB-Chain, and evaluated its performance through large-scale blockchain deployment using real-world transaction traces. Extensive experiments confirm that LB-Chain significantly boosts sharding performance, reducing the transaction confirmation delays by up to 90% while increasing the transaction throughput by more than 10%. The delay difference between different accounts is also reduced dramatically, leading to improved fairness in the system.