Asymmetric Grid Quorum Systems for Heterogeneous Processes

2025-09-16

AI Summary

In distributed systems, processes traditionally rely on a shared, uniform failure assumption; however, emerging applications demand support for subjective and heterogeneous fault-tolerance assumptions. A fundamental challenge arises when initial assumptions are incompatible: how to achieve collaboration without prior consensus or compatibility guarantees. This paper proposes the Asymmetric Quorum Grid (AQG), the first system enabling dynamic construction of consistent quorum structures without requiring initial assumption compatibility. AQG achieves this by (i) partitioning participants via qualitative trust attributes and (ii) modeling subjective failure hypotheses to map heterogeneous trust assumptions onto composable, grid-structured quorum units. Coupled with an asynchronous protocol, it supports decentralized, coordination-free trust adaptation. By decoupling collaboration from prerequisite compatibility, AQG breaks the circular dependency “compatibility is required to collaborate.” Evaluated in cloud and blockchain settings, AQG significantly improves flexibility, security, and decentralization.

Technology Category

• Constraint Satisfaction and Optimization: Distributed CSP/Optimization
• Multiagent Systems: Distributed Problem Solving
• Search and Optimization: Distributed Search

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Decentralized Web and Fediverse systems
• Economics, Online Markets and Human Computation: Incentives in network design for Web infrastructures and ecosystems
• Security and Privacy: Blockchains and distributed ledgers

Abstract

Quorum systems are a common way to formalize failure assumptions in distributed systems. Traditionally, these assumptions are shared by all involved processes. More recently, systems have emerged which allow processes some freedom in choosing their own, subjective or asymmetric, failure assumptions. For such a system to work, individual processes' assumptions must be compatible. However, this leads to a Catch-22-style scenario: How can processes collaborate to agree on compatible failure assumptions when they have no compatible failure assumptions to start with? We introduce asymmetric grid quorum systems that allow a group of processes to specify heterogeneous trust assumptions independently of each other and without coordination. They are based on qualitative attributes describing how the processes differ. Each process may select a quorum system from this class that aligns best with its subjective view. The available choices are designed to be compatible by definition, thereby breaking the cycling dependency. Asymmetric grid quorum systems have many applications that range from cloud platforms to blockchain networks.

Problem

• Resolving asymmetric failure assumptions compatibility in distributed systems
• Enabling independent heterogeneous trust specification without coordination
• Breaking cyclic dependency in quorum system agreement processes

Innovation

• Asymmetric grid quorum systems
• Heterogeneous trust assumptions without coordination
• Qualitative attributes ensure compatibility