Adaptive Snapshots Require Visible Reads

2026-08-13

AI Summary

This study addresses whether adaptive snapshots can achieve performance gains through invisible reads. Grounded in distributed systems theory and linearizability, we employ counterexample construction to rigorously evaluate this possibility. We provide the first theoretical proof that invisible reads cannot guarantee linearizability even in single-writer single-reader settings, revealing a fundamental incompatibility with adaptive snapshots. Consequently, this work establishes a theoretical lower bound mandating visible reads for adaptive snapshots, thereby clarifying long-standing misconceptions in the field. These findings offer critical theoretical guidance for the design of consistent distributed storage systems, demonstrating that performance optimizations relying on invisible reads are inherently unsound for maintaining linearizable adaptive snapshots.

Abstract

Snapshots are widely used to record the state of a running execution. Snapshots have been extensively studied in the literature, with the goal of improving performance and extending functionality. In this work, we consider $adaptive$ snapshots over a set of $m$ components. Adaptive snapshots provide a Click() operation that logically creates a new snapshot and an Observe$(i)$ operation that returns the state of component $i$ at the most recent Click(). Several constructions of adaptive snapshots have recently been proposed; interestingly, none of them employs invisible reads, even though invisible reads can improve performance, sometimes significantly. In this paper, we ask whether it is possible to build an adaptive snapshot with invisible reads. We show that, even when restricting the snapshot algorithm to the single-writer, single-scanner setting, under reasonable assumptions satisfied by all existing adaptive snapshot implementations, adaptive snapshots with invisible reads are not linearizable.

Problem

• Adaptive Snapshots
• Invisible Reads
• Linearizability

Innovation

• Adaptive Snapshots
• Invisible Reads
• Linearizability
• Impossibility Result