Practically-self-stabilizing virtual synchrony

Abstract

The virtual synchrony abstraction was proven to be extremely useful for asynchronous, large-scale, message-passing distributed systems. Self-stabilizing systems can automatically regain consistency after the occurrence of transient faults.We present the first practically-self-stabilizing virtual synchrony algorithm that uses a new counter algorithm that establishes an efficient practically unbounded counter, which in turn can be directly used for emulating a self-stabilizing Multiple-Writer Multiple-Reader (MWMR). Other self-stabilizing services include membership, multicast, and replicated state machine (RSM) emulation. As we base the latter on virtual synchrony, rather than consensus, the system can progress in more extreme asynchronous executions than consensus-based RSM emulations. * A preliminary version of this work has appeared in the proceedings of the 17th International Symposium on Stabilization, Safety, and Security of Distributed Systems (SSS'15 ).Transient faults Transient violations of design assumptions can lead a system to an arbitrary state. For example, the assumption that error detection ensures the arrival of correct messages and the discarding of corrupted messages, might be violated since error detection is a probabilistic mechanism that may not detect a corrupt message. As a result, the message can be regarded as legitimate, driving the system to an arbitrary state after which, availability and functionality may be damaged forever, requiring human intervention. In the presence of transient faults, large multicomputer systems providing VS-based services can prove hard to manage and control. One key problem, not restricted to virtually synchronous systems, is catering for counters (such as view identifiers) reaching an arbitrary value. How can we deal with the fact that transient faults may force counters to wrap around to the zero value and violate important system assumptions and correctness invariants, such as the ordering of events? A self-stabilizing algorithm [13] can automatically recover from such unexpected failures, possibly as part of after-disaster recovery or even after benign temporal violations of the assumptions made in the design of the system. To the best of our knowledge, no stabilizing virtual synchrony solution exists. We tackle this issue in our work.Practically-self-stabilization A relatively new self-stabilization paradigm is practically-selfstabilization [1,7,16]. Consider an asynchronous system with bounded memory and data link capacity in which corrupt pieces of data (stale information) exist due to a transient fault. (Recall that transient faults can result in the appearance of corrupted information, which the system tends to spread and thus reach an arbitrary state.) These corrupted data may appear unexpectedly at any processor as they lie in communication links, or may (indefinitely) remain "hidden" in some processor's local memory until they are added to the communication links as a response to some other processor's input. Whilst these pieces of corrupted data ...

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