Crossword: Adaptive Consensus for Dynamic Data-Heavy Workloads

2025-09-08

AI Summary

To address bandwidth pressure surges and consensus performance bottlenecks caused by dynamic, data-intensive workloads in cloud environments, this paper proposes FlexConsensus—a self-adaptive consensus protocol. Its key contributions are: (1) instance-level erasure coding to reduce transmission overhead on the critical path; (2) joint optimization of dynamic sharding and quorum size to enhance throughput elasticity while preserving linearizability and fault tolerance; and (3) a lazy-follower gossip mechanism enabling low-overhead leader failure recovery. Implemented in async Rust atop the generic KV store Gazette, FlexConsensus maintains compatibility with MultiPaxos and Raft availability models. Experimental evaluation demonstrates a 2.3× throughput improvement over MultiPaxos and Raft under dynamic workloads. When integrated into CockroachDB, it achieves a 1.32× speedup in TPC-C throughput, validating its effectiveness in production-grade distributed databases.

Technology Category

• Search and Optimization: Distributed Search
• Constraint Satisfaction and Optimization: Distributed CSP/Optimization
• Data Mining & Knowledge Management: Scalability, Parallel & Distributed Systems

Application Category

• Security and Privacy: Data transparency and provenance
• Responsible Web: Consent frameworks and practices on the web
• Graph Algorithms and Modeling for the Web: Efficient manipulation of static and dynamic Web-related graphs

Abstract

We present Crossword, a flexible consensus protocol for dynamic data-heavy workloads, a rising challenge in the cloud where replication payload sizes span a wide spectrum and introduce sporadic bandwidth stress. Crossword applies per-instance erasure coding and distributes coded shards intelligently to reduce critical-path data transfer significantly when desirable. Unlike previous approaches that statically assign shards to servers, Crossword enables an adaptive tradeoff between the assignment of shards and quorum size in reaction to dynamic workloads and network conditions, while always retaining the availability guarantee of classic protocols. Crossword handles leader failover gracefully by employing a lazy follower gossiping mechanism that incurs minimal impact on critical-path performance. We implement Crossword (along with relevant protocols) in Gazette, a distributed, replicated, and protocol-generic key-value store written in async Rust. We evaluate Crossword comprehensively to show that it matches the best performance among previous protocols (MultiPaxos, Raft, RSPaxos, and CRaft) in static scenarios, and outperforms them by up to 2.3x under dynamic workloads and network conditions. Our integration of Crossword with CockroachDB brings 1.32x higher aggregate throughput to TPC-C under 5-way replication. We will open-source Gazette upon publication.

Problem

• Handles dynamic data-heavy workloads with varying payload sizes
• Reduces critical-path data transfer via adaptive erasure coding
• Maintains availability guarantees under changing network conditions

Innovation

• Adaptive erasure coding for dynamic workloads
• Intelligent shard distribution reduces data transfer
• Lazy follower gossiping for graceful failover