LB-Louvain: Balancing Transaction Locality and Shard Load in Account-Based State Sharding

Account-based state sharding improves blockchain parallelism by distributing account states and transaction execution across physical shards, but effective placement must preserve transaction locality without concentrating processing demand on a small number of shards. This paper presents LB-Louvain, a coarse-to-fine account-partitioning heuristic in which standard Louvain first extracts logical communities, followed by load-aware community-to-shard assignment and restricted boundary-account refinement. In controlled BlockEmulator experiments using 300,000 replayed Ethereum transactions and five repeated system runs per configuration, relative to CLPA, the complete LB-Louvain pipeline reduces the mean cross-shard transaction ratio by approximately 2.1%, increases active throughput by approximately 19.7%, and reduces average confirmation latency by approximately 9.4%. Component-wise ablation confirms complementary roles for load-aware assignment and boundary refinement. The evaluated behavior remains stable over β∈[1,4], while partition-only profiling keeps the measured partition computation below 100 ms across the tested 50,000–300,000 transaction prefixes and 4–24 physical shards. An auxiliary migration experiment further shows that Fine-Grained activation reduces the observed migration-deferred set by approximately 39.8% relative to Full Locking while maintaining comparable throughput and confirmation latency. Broader archived experiments with Monoxide and CLPA are retained separately from the controlled revision results.