Sharding is one of the most promising technologies for significantly increasing blockchain transaction throughput. However, as the number of shards increases, the ratio of cross-shard transactions in existing blockchain sharding protocols gradually approaches 100%. Since cross-shard transactions consume many times more resources than intra-shard transactions, the processing overhead of cross-shard transactions already accounts for the majority of the total overhead of the sharding system. There is a very large gap between the transaction throughput of the sharding system and its theoretical upper limit. In this article, we propose Estuary, a novel low cross-shard blockchain sharding protocol. Taking the state model as an entry point, Estuary designs a multi-level state model and state splitting and aggregation mechanism. It decouples the identity and quantity of state units, enabling transactions between users to be completed within one shard. Only when the state quantity for all shards of a user is insufficient a small number of cross-shard transactions are required. On this basis, we propose a community overlap propagation algorithm for sharding. It defines the users’ belonging coefficients of each shard and optimizes the state distribution so that the state distribution can better match the transaction characteristics between users. Finally, we develop an analysis framework for the sharding protocol and experiment with real Bitcoin transactions. The evaluation results show that compared to the state-of-the-art sharding protocol, Estuary reduces the ratio of cross-shard transactions by 88.54% and achieves more than 1.85 times the throughput improvement (92.98% of the theoretical upper limit).

In the Interplanetary File System (IPFS), consumers can help each other protect data against hardware failures and improve data availability through replication. While previous replication methods in peer-to-peer (P2P) networks can be used to increase data availability in the IPFS network, they are either hostile to peers with limited availability, preventing them from achieving adequate data availability, or lack flexibility. An ideal replication method should optimize data availability in a manner equitable to all peers while providing flexibility. To achieve this goal, this paper introduces a blockchain-based file replication mechanism. Leveraging the non-tamperable and traceable nature of blockchain technology, our mechanism achieves secure storage and trustworthy query of peers’ information used in the file replication process. Unlike most earlier methods, our mechanism employs an Arweave-inspired file replication algorithm that prioritizes the less available files within the system for replication until all files’ availabilities are optimized. Replicating files according to predefined system-wide cooperation rules like this not only limits the selfishness of peers but also facilitates timely adjustments in response to changes in the P2P system. In addition, our mechanism also uses smart contracts to judge and exclude dishonest peers, thereby fostering honest cooperation among peers without involving any third party.

The account allocation mechanism is a crucial component affecting the performance of sharding blockchain systems. A well-designed account allocation mechanism must reduce the number of cross-shard transactions while balancing the workload across shards. State-of-the-art mechanisms, which are semi-static, typically adjust account partitions based on historical transactions at regular intervals. However, in real-world applications, unpredictable new scenarios in historical transactions or sudden workload changes can impact shard performance. These existing mechanisms can neither foresee such scenarios to avoid cross-shard transactions nor dynamically adjust account partitions to improve workload issues, leading to suboptimal performance until the next re-allocation. To this end, we propose Orbit, a dynamic account allocation mechanism based on the pending transactions in the pool. Orbit can promptly detect new situations and changes in pending transactions and provide updated allocation strategies. Moreover, through its off-chain scheduling mechanism, Orbit can deploy these strategies before transaction packaging to enhance shard performance. Experimental results show that compared to the state-of-the-art allocation mechanisms, Orbit improves throughput by 2.02 times, reduces cross-shard transactions to 11.9%, and achieves a more balanced shard workload. Additionally, Orbit excels in various other aspects, including latency, transaction queue size, and bandwidth overhead, outperforming the state-of-the-art mechanisms.

Sharding is a prevalent approach for addressing performance issues in blockchain. To reduce governance complexities and ensure system security, a common practice involves a relay chain to coordinate cross-shard transactions. However, with a growing number of shards and cross-shard transactions, the single relay chain usually first suffers from performance bottleneck and shows poor scalability, thus making the relay chain's scalability vital for sharding systems. To solve this, we propose Mitosis, the first multi-relay architecture to improve the relay chain's scalability by sharding the relay chain itself. Our proposed relay sharding algorithm dynamically adjusts the number of relays or optimizes the topology between relays and shards to adaptively scale up relay chain's performance. Furthermore, to guarantee the security of the multi-relay architecture, a new validator reconfiguration scheme is designed, accompanied by a comprehensive security analysis of Mitosis. Through simulation experiments on two mainstream relay chain paradigms, we demonstrate that Mitosis can achieve high scalability and outperform state-of-the-art baselines in terms of workload of relays, relay chain throughput, and transaction latency