A Hierarchical Sharded Blockchain Balancing Performance and Availability

TL;DR

PyloChain is a hierarchical sharded blockchain that balances performance and availability by combining local chains with a main DAG-based chain for cross-shard transactions, achieving higher throughput and lower latency.

Contribution

It introduces PyloChain, a novel hierarchical sharding architecture that balances availability and performance, with a DAG-based main chain and speculative local transaction execution.

Findings

Achieves 1.49x higher throughput than state-of-the-art.

Reduces latency by 2.63x compared to existing solutions.

Provides a fine-grained auditing mechanism for fault mitigation.

Abstract

Blockchain networks offer decentralization, transparency, and immutability for managing critical data but encounter scalability problems as the number of network members and transaction issuers grows. Sharding is considered a promising solution to enhance blockchain scalability. However, most existing blockchain sharding techniques prioritize performance at the cost of availability (e.g., a failure in a few servers holding a shard leads to data unavailability). In this paper, we propose PyloChain, a hierarchical sharded blockchain that balances availability and performance. PyloChain consists of multiple lower-level local chains and one higher-level main chain. Each local chain speculatively executes local transactions to achieve high parallelism across multiple local chains. The main chain leverages a directed-acyclic-graph (DAG)-based mempool to guarantee local block availability and to enable efficient Byzantine Fault Tolerance (BFT) consensus to execute global (or cross-shard) transactions within a collocated sharding. PyloChain speculatively executes local transactions across multiple local chains to achieve high parallelism. In order to reduce the number of aborted local transactions, PyloChain applies a simple scheduling technique to handle global transactions in the main chain. PyloChain provides a fine-grained auditing mechanism to mitigate faulty higher-level members by externalizing main chain operations to lower-level local members. We implemented and evaluated PyloChain, demonstrating its performance scalability with 1.49x higher throughput and 2.63x faster latency compared to the state-of-the-art balanced hierarchical sharded blockchain.