Monotonic Prefix Consistency in Distributed Systems

TL;DR

This paper investigates the limits of data consistency in distributed systems that are available and partition-tolerant, establishing Monotonic Prefix Consistency as the strongest achievable criterion.

Contribution

It proves that no consistency criterion stronger than Monotonic Prefix Consistency can be implemented in such distributed systems.

Findings

Monotonic Prefix Consistency is the strongest achievable consistency.

No stronger consistency criterion than MPC can be implemented.

The study clarifies the limits of consistency in available, partition-tolerant systems.

Abstract

We study the issue of data consistency in distributed systems. Specifically, we consider a distributed system that replicates its data at multiple sites, which is prone to partitions, and which is assumed to be available (in the sense that queries are always eventually answered). In such a setting, strong consistency, where all replicas of the system apply synchronously every operation, is not possible to implement. However, many weaker consistency criteria that allow a greater number of behaviors than strong consistency, are implementable in available distributed systems. We focus on determining the strongest consistency criterion that can be implemented in a convergent and available distributed system that tolerates partitions. We focus on objects where the set of operations can be split into updates and queries. We show that no criterion stronger than Monotonic Prefix Consistency (MPC) can be implemented.