Towards Establishing Monotonic Searchability in Self-Stabilizing Data Structures (full version)

TL;DR

This paper introduces a self-stabilizing overlay network protocol that guarantees monotonic searchability during recovery, ensuring reliable message delivery despite network changes and node departures, with a focus on the line topology.

Contribution

It presents the first protocol achieving monotonic searchability in self-stabilizing overlay networks, specifically for the line topology, and extends it to handle node departures.

Findings

Monotonic searchability is impossible with corrupted messages.

A self-stabilizing protocol for the line with monotonic searchability is proposed.

The protocol is extended to support node departures.

Abstract

Distributed applications are commonly based on overlay networks interconnecting their sites so that they can exchange information. For these overlay networks to preserve their functionality, they should be able to recover from various problems like membership changes or faults. Various self-stabilizing overlay networks have already been proposed in recent years, which have the advantage of being able to recover from any illegal state, but none of these networks can give any guarantees on its functionality while the recovery process is going on. We initiate research on overlay networks that are not only self-stabilizing but that also ensure that searchability is maintained while the recovery process is going on, as long as there are no corrupted messages in the system. More precisely, once a search message from node $u$ to another node $v$ is successfully delivered, all future search messages from $u$ to $v$ succeed as well. We call this property monotonic searchability. We show that in general it is impossible to provide monotonic searchability if corrupted messages are present in the system, which justifies the restriction to system states without corrupted messages. Furthermore, we provide a self-stabilizing protocol for the line for which we can also show monotonic searchability. It turns out that even for the line it is non-trivial to achieve this property. Additionally, we extend our protocol to deal with node departures in terms of the Finite Departure Problem of Foreback et. al (SSS 2014). This makes our protocol even capable of handling node dynamics. This is the full version of a correspondent paper published at OPODIS'15.