Did we miss P In CAP? Partial Progress Conjecture under Asynchrony

TL;DR

This paper explores the Partial Progress Conjecture under asynchrony, proposing a new consensus protocol that enables some progress during network partitions, balancing consistency and availability.

Contribution

It introduces the CASSANDRA consensus protocol, demonstrating partial progress under network partitions to improve system responsiveness.

Findings

CASSANDRA allows partitioned replicas to order requests.

Partial progress improves responsiveness during failures.

The protocol balances consistency and availability under asynchrony.

Abstract

Each application developer desires to provide its users with consistent results and an always-available system despite failures. Boldly, the CALM theorem disagrees. It states that it is hard to design a system that is both consistent and available under network partitions; select at most two out of these three properties. One possible solution is to design coordination-free monotonic applications. However, a majority of real-world applications require coordination. We resolve this dilemma by conjecturing that partial progress is possible under network partitions. This partial progress ensures the system appears responsive to a subset of clients and achieves non-zero throughput during failures. To this extent, we present the design of our CASSANDRA consensus protocol that allows partitioned replicas to order client requests.