Manifoldchain: Maximizing Blockchain Throughput via Bandwidth-Clustered Sharding

TL;DR

Manifoldchain tackles the bandwidth bottleneck in PoW blockchains by introducing bandwidth-aware shard formation and a sharing mining paradigm that distributes honest hashing power across all shards. The approach includes asynchronous cross-shard commitment and data-availability verification via coded Merkle trees, backed by a formal security analysis that proves CP, CQ, and CG under a mildly adaptive adversary. The authors implement a Rust prototype and demonstrate substantial throughput improvements both horizontally (more shards) and vertically (higher bandwidth) compared to state-of-the-art full sharding protocols, with real-world experiments and simulated tests showing significant gains. This work has practical implications for scalable, secure PoW systems by leveraging bandwidth heterogeneity rather than treating all miners equivalently, and it provides a framework that could extend to PoS and permissioned settings.

Abstract

Bandwidth limitation is the major bottleneck that hinders scaling throughput of proof-of-work blockchains. To guarantee security, the mining rate of the blockchain is determined by the miners with the lowest bandwidth, resulting in an inefficient bandwidth utilization among fast miners. We propose Manifoldchain, an innovative blockchain sharding protocol that alleviates the impact of slow miners to maximize blockchain throughput. Manifoldchain utilizes a bandwidth-clustered shard formation mechanism that groups miners with similar bandwidths into the same shard. Consequently, this approach enables us to set an optimal mining rate for each shard based on its bandwidth, effectively reducing the waiting time caused by slow miners. Nevertheless, the adversary could corrupt miners with similar bandwidths, thereby concentrating hashing power and potentially creating an adversarial majority within a single shard. To counter this adversarial strategy, we introduce sharing mining, allowing the honest mining power of the entire network to participate in the secure ledger formation of each shard, thereby achieving the same level of security as an unsharded blockchain. Additionally, we introduce an asynchronous atomic commitment mechanism to ensure transaction atomicity across shards with various mining rates. Our theoretical analysis demonstrates that Manifoldchain scales linearly in throughput with the increase in shard numbers and inversely with network delay in each shard. We implement a full system prototype of Manifoldchain, comprehensively evaluated on both simulated and real-world testbeds. These experiments validate its vertical scalability with network bandwidth and horizontal scalability with network size, achieving a substantial improvement of 186% in throughput over baseline sharding protocols, for scenarios where bandwidths of miners range from 5Mbps to 60Mbps.

Figures (17)

• Figure 1: Basic insight of Manifoldchain. The hindrance imposed by bandwidth heterogeneity is alleviated by gathering the stragglers.
• Figure 2: USF vs BCSF. The first one uniformly distributes miners across shards while the second one clusters miners with similar bandwidths.
• Figure 3: Overview of sharing mining. An exclusive block extends the blockchain within a specific shard, whereas an inclusive block extends all blockchains across shards.
• Figure 4: Key insight of predictive mining and fork pruning. Blocks can extend potential parents and invalid forks are subsequently pruned.
• Figure 5: The proof roadmap of Theorem \ref{['informal_cp_property']} and \ref{['informal_tps_theorem']}.

Theorems & Definitions (50)

• Definition 1
• Lemma 1
• Theorem 1
• Theorem 2: Informal
• Definition 2
• Lemma 2
• proof
• Theorem 3: Cross-shard transaction atomicity
• proof
• Definition 3