Differentiated Consistency for Worldwide Gossips

• Published in: IEEE transactions on parallel and distributed systems Vol. 34; no. 1; pp. 1 - 15
• Main Authors: Frey, Davide, Mostefaoui, Achour, Perrin, Matthieu, Roman, Pierre-Louis, Taiani, Francois
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.01.2023; The Institute of Electrical and Electronics Engineers, Inc. (IEEE); Institute of Electrical and Electronics Engineers
• Subjects: Blockchain; Blockchains; Clocks; Computer networks; Computer Science; Consistency; Convergence; Cryptography; Cryptography and Security; Data structures; Delays; Distributed system; Distributed, Parallel, and Cluster Computing; epidemic protocol; Epidemiology; eventual consistency; Nodes; Protocols; Safety; Uninterruptible power systems; Eventual consistency; Distributed system; Epidemic protocol; Blockchain
• ISSN: 1045-9219; 1558-2183
• DOI: 10.1109/TPDS.2022.3209150

Eventual consistency is a consistency model that favors liveness over safety. It is often used in large-scale distributed systems where models ensuring a stronger safety incur performance that are too low to be deemed practical. Eventual consistency tends to be uniformly applied within a system, but we argue a demand exists for differentiated eventual consistency, e.g. in blockchain systems. We propose update-query consistency with primaries and secondaries (UPS) to address this demand. UPS is a novel consistency mechanism that works in pair with our novel two-phase epidemic broadcast protocol gossip primary-secondary (GPS) to offer differentiated eventual consistency and delivery speed. We propose two complementary analyses of the broadcast protocol: a continuous analysis and a discrete analysis based on compartmental models used in epidemiology. Additionally, we propose the formal definition of a scalable consistency metric to measure the consistency trade-off at runtime. We evaluate UPS in two simulated worldwide settings: a one-million-node network and a network emulating that of the Ethereum blockchain. In both settings, UPS reduces inconsistencies experienced by a majority of the nodes and reduces the average message latency for the remaining nodes.