On the Power of False Negative Awareness in Indicator-based Caching Systems

TL;DR

This paper investigates the impact of false negatives in indicator-based distributed caching systems, proposing new policies that reduce access costs by accounting for false-negative indications caused by indicator staleness.

Contribution

It introduces false-negative aware access policies that estimate false-negative ratios and adapt cache access strategies, with optimal solutions for homogeneous cases and approximation guarantees for heterogeneous cases.

Findings

False-negative aware algorithms significantly reduce access costs.

Proposed policies require fewer resources compared to existing methods.

Simulation results validate the effectiveness of the new policies.

Abstract

Distributed caching systems such as content distribution networks often advertise their content via lightweight approximate indicators (e.g., Bloom filters) to efficiently inform clients where each datum is likely cached. While false-positive indications are necessary and well understood, most existing works assume no false-negative indications. Our work illustrates practical scenarios where false-negatives are unavoidable and ignoring them has a significant impact on system performance. Specifically, we focus on false-negatives induced by indicator staleness, which arises whenever the system advertises the indicator only periodically, rather than immediately reporting every change in the cache. Such scenarios naturally occur, e.g., in bandwidth-constraint environments or when latency impedes the ability of each client to obtain an updated indicator. Our work introduces novel false-negative aware access policies that continuously estimate the false-negative ratio and sometimes access caches despite negative indications. We present optimal policies for homogeneous settings and provide approximation guarantees for our algorithms in heterogeneous environments. We further perform an extensive simulation study with multiple real system traces. We show that our false-negative aware algorithms incur a significantly lower access cost than existing approaches or match the cost of these approaches while requiring an order of magnitude fewer resources (e.g., caching capacity or bandwidth).