Presto: Optimizing Cross-Shard Transactions in Sharded Blockchain Architecture

Blockchain sharding technology has been used to enhance the scalability of blockchain systems. As the number of shards increases, the high latency inherent in cross-shard transactions gradually becomes a bottleneck, hindering improvements in overall system efficiency. Therefore, reducing the latency of cross-shard transactions is significantly important. However, existing mechanisms for handling cross-shard transactions fail to minimize the latency of cross-shard transactions and have not fully used the bandwidth available within shards. In this paper, we introduce Presto, a protocol designed for the account-state-based blockchain, which reduces the latency of handling cross-shard transactions. Presto leverages the concept of optimistic pre-execution along with pending tree to optimize cross-shard transaction processing. Presto also employs predistribution of cross-shard transactions with Erasure Coding to efficiently utilize bandwidth resources. We have developed an prototype and conducted extensive experiments on a cloud platform. The evaluation results indicate that Presto surpasses existing solutions in terms of system throughput, transaction confirmation latency, and mempool queue size, demonstrating Presto's potential to significantly improve blockchain scalability and user experience.