Petr Kouznetsov

PeerReview: practical accountability for distributed systems

We describe PeerReview, a system that provides accountability in distributed systems. PeerReview ensures that Byzantine faults whose effects are observed by a correct node are eventually detected and irrefutably linked to a faulty node. At the same time, PeerReview ensures that a correct node can always defend itself against false accusations. These guarantees are particularly important for systems that span multiple administrative domains, which may not trust each other.PeerReview works by maintaining a secure record of the messages sent and received by each node. The record isused to automatically detect when a nodes behavior deviates from that of a given reference implementation, thus exposing faulty nodes. PeerReview is widely applicable: it only requires that a correct nodes actions are deterministic, that nodes can sign messages, and that each node is periodically checked by a correct node. We demonstrate that PeerReview is practical by applying it to three different types of distributed systems: a network filesystem, a peer-to-peer system, and an overlay multicast system.

Mutual exclusion in asynchronous systems with failure detectors

This paper considers the fault-tolerant mutual exclusion problem in a message-passing asynchronous system and determines the weakest failure detector to solve the problem, given a majority of correct processes. This failure detector, which we call the trusting failure detector, and which we denote by T, is strictly weaker than the perfect failure detector P but strictly stronger than the eventually perfect failure detector @?P. The paper shows that a majority of correct processes is necessary to solve the problem with T. Moreover, T is also the weakest failure detector to solve the fault-tolerant group mutual exclusion problem, given a majority of correct processes.

The weakest failure detectors to boost obstruction-freedom

It is considered good practice in concurrent computing to devise shared object implementations that ensure a minimal obstruction-free progress property and delegate the task of boosting liveness to independent generic oracles called contention managers. This paper determines necessary and sufficient conditions to implement wait-free and non-blocking contention managers, i.e., contention managers that ensure wait-freedom (resp. non-blockingness) of any associated obstruction-free object implementation. The necessary conditions hold even when universal objects (like compare-and-swap) or random oracles are available in the implementation of the contention manager. On the other hand, the sufficient conditions assume only basic read/write objects, i.e., registers. We show that failure detector

On the weakest failure detector ever

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Synchronizing without locks is inherently expensive

is the weakest to convert any obstruction-free algorithm into a wait-free one, and Ω*, a new failure detector which we introduce in this paper, and which is strictly weaker than

On Failure Detectors and Type Boosters

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