Asynchronous failure detectors

Abstract

Failure detectors -oracles that provide information about process crashes -are an important abstraction for crash tolerance in distributed systems. Although current failuredetector theory provides great generality and expressiveness, it also poses significant challenges in developing a robust hierarchy of failure detectors. We address some of these challenges by proposing a variant of failure detectors called asynchronous failure detectors and an associated modeling framework. Unlike the traditional failure-detector framework, our framework eschews real time completely. We show that asynchronous failure detectors are sufficiently expressive to include several popular failure detectors. Additionally, we show that asynchronous failure detectors satisfy many desirable properties: they are self-implementable, guarantee that stronger asynchronous failure detectors solve more problems, and ensure that their outputs encode no information other than process crashes. We introduce the notion of a failure detector being representative of a problem to capture the idea that some problems encode the same information about process crashes as their weakest failure detectors do. We show that a large class of problems, called finite problems, do not have representative failure detectors.

Consensus using Asynchronous Failure Detectors

“…In [5,6] we introduced a new formulation of failure detectors. Unlike the traditional failure detectors of [3,2], ours are modeled as asynchronous automata, and defined in terms of the general I/O automata framework for asynchronous concurrent systems.…”

“…Our model narrowed the scope of failure detectors sufficiently so that AFDs satisfy several desirable properties, which are not true of the general class of traditional failure detector. For example, (1) AFDs are self-implementable; (2) if an AFD D is strictly stronger than another AFD D, then D is sufficient to solve a strict superset of the problems solvable by D. See [6] for details. Working entirely within an asynchronous framework allowed us to take advantage of the general results about I/O automata and to prove our results rigorously without too much difficulty.…”

“…Since our framework is entirely asynchronous and all our definitions are based on an established concurrency theory foundation, we are able to provide rigorous proofs for the (unproven) assertions from [2]. In order to prove the main result of this paper, we modified certain definitions from [6]. However, these modifications do not invalidate any of the results from [5,6].…”

“…In order to prove the main result of this paper, we modified certain definitions from [6]. However, these modifications do not invalidate any of the results from [5,6].…”

Solvability-Based Comparison of Failure Detectors

“…In the work presented here, we focus on this assumption and explore the nature of relations that compare failure detectors. Incidentally, the robustness of the CT relation has been challenged in recent work [JT08,CBHW10,CLS12,CLS13], where it was observed that the relation has several drawbacks; for instance, CT is not reflexive. To overcome the drawbacks of the CT relation, new relations have been proposed in [JT08] and [CBHW10].…”