LFAMLedger: Account Migration Across Blockchain Shards Using a Lock-Free Mechanism

With the development of sharded blockchains, account migration mechanisms migrate accounts selected by account partition algorithms from the source shard to the target shard, aiming to reduce cross-shard transactions and balance the load. Moreover, the cost of account migration plays a critical role in determining the effectiveness of partitioning algorithms, as performance gains from resharding depend on cost-efficiency. Therefore, an efficient and low-overhead migration mechanism is critical to improving the performance of sharded blockchains. Existing migration approaches require cross-shard locks or intra-shard locks, which causes service interruption. However, we observe that account states remain unchanged during migration, indicating that such lock-based mechanisms are overly restrictive. To this end, we propose a novel Lock-Free Account Migration ledger, denoted as LFAMLedger, which consists of a prewrite phase and a migration phase. LFAMLedger ensures data consistency and lock-free migration through timestamp-based multi-version snapshots and a deferred validation mechanism. Furthermore, we propose optimistic snapshot isolation to decouple the source and target shards, and a flexible strategy to enable concurrent migration of accounts and their associated transactions to multiple target shards. We conduct extensive scalability experiments based on real Ethereum transaction histories. Compared with cross-shard lock-based and intra-shard lock-based migration approaches, our lock-free LFAMLedger achieves 1.9× and 1.8× higher throughput, and reduces latency by 2.35× and 1.75×, respectively, demonstrating significant improvements in efficiency.