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The ubiquity of distributed agreement protocols, such as consensus, has galvanized interest in verification of such protocolsas well asapplications built on top of them. The complexity and unboundedness of such systems, however, makes their verification onerous in general, and, particularly prohibitive for full automation. An exciting, recent breakthrough reveals that, through careful modeling, it becomes possible to reduce verification of interesting distributed agreement-based (DAB) systems, that are unbounded in the number of processes, to model checking of small, finite-state systems. It is an open question if such reductions are also possible for DAB systems that aredoubly-unbounded, in particular, DAB systems that additionally have unbounded data domains. We answer this question in the affirmative in this work thereby broadening the class of DAB systems which can be automatically and efficiently verified. We present a novel reduction which leveragesvalue symmetryand a new notion ofdata saturationto reduce verification of doubly-unbounded DAB systems to model checking of small, finite-state systems. We develop a tool, Venus, that can efficiently verify sophisticated DAB system models such as the arbitration mechanism for a consortium blockchain, a distributed register, and a simple key-value store. 

Distributed agreement-based (DAB) systems use common distributed agreement protocols such as leader election and consensus as building blocks for their target functionality. While automated verification for DAB systems is undecidable in general, recent work identifies a large class of DAB systems for which verification is efficiently-decidable. Unfortunately, the conditions characterizing such a class can be opaque and non-intuitive, and can pose a significant challenge to system designers trying to model their systems in this class. In this paper, we present a synthesis-driven tool, CINNABAR, to help system designers building DAB systems ensure that their intended designs belong to an efficiently-decidable class. In particular, starting from an initial sketch provided by the designer, CINNABAR generates sketch completions using a counterexample-guided procedure. The core technique relies on compactly encoding root-causes of counterexamples to varied properties such as efficient-decidability and safety. We demonstrate CINNABAR ’s effectiveness by successfully and efficiently synthesizing completions for a variety of interesting DAB systems including a distributed key-value store and a distributed consortium system. 

The last decade has sparked several valiant efforts in deductive verification of distributed agreement protocols such as consensus and leader election. Oddly, there have been far fewer verification efforts that go beyond the core protocols and target applications that are built on top of agreement protocols. This is unfortunate, as agreement-based distributed services such as data stores, locks, and ledgers are ubiquitous and potentially permit modular, scalable verification approaches that mimic their modular design. We address this need for verification of distributed agreement-based systems through our novel modeling and verification framework, QuickSilver, that is not only modular, but also fully automated. The key enabling feature of QuickSilver is our encoding of abstractions of verified agreement protocols that facilitates modular, decidable, and scalable automated verification. We demonstrate the potential of QuickSilver by modeling and efficiently verifying a series of tricky case studies, adapted from real-world applications, such as a data store, a lock service, a surveillance system, a pathfinding algorithm for mobile robots, and more. 

Inspired by distributed applications that use consensus or other agreement protocols for global coordination, we define a new computational model for parameterized systems that is based on a general global synchronization primitive and allows for global transition guards. Our model generalizes many existing models in the literature, including broadcast protocols and guarded protocols. We show that reachability properties are decidable for systems without guards, and give sufficient conditions under which they remain decidable in the presence of guards. Furthermore, we investigate cutoffs for reachability properties and provide sufficient conditions for small cutoffs in a number of cases that are inspired by our target applications