Asynchronous Latency and Fast Atomic Snapshot

TL;DR

This paper presents a new fast atomic-snapshot protocol for asynchronous systems, introduces a unifying latency metric, and demonstrates improved latency bounds over existing protocols.

Contribution

It proposes a novel atomic-snapshot algorithm with formally analyzed latency improvements using a new unifying time-complexity metric.

Findings

Optimal latency in fault-free runs without contention

Constant latency in fault-free runs with contention

Latency proportional to active failures in worst case

Abstract

This paper introduces a novel, fast atomic-snapshot protocol for asynchronous message-passing systems. In the process of defining what ``fast'' means exactly, we spot a few interesting issues that arise when conventional time metrics are applied to long-lived asynchronous algorithms. We reveal some gaps in latency claims made in earlier work on snapshot algorithms, which hamper their comparative time-complexity analysis. We then come up with a new unifying time-complexity metric that captures the latency of an operation in an asynchronous, long-lived implementation. This allows us to formally grasp latency improvements of our atomic-snapshot algorithm with respect to the state-of-the-art protocols: optimal latency in fault-free runs without contention, short constant latency in fault-free runs with contention, the worst-case latency proportional to the number of active concurrent failures, and constant, amortized latency.