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International audienceFailure detection plays a central role in the engineering of distributed systems. Furthermore, many applications have timing constraints and require failure detectors that provide quality of service (QoS) with some quantitative timeliness guarantees. Therefore, they need failure detectors that are fast and accurate. We introduce the Two Windows Failure Detector (2W-FD), an algorithm that provides QoS and is able to react to sudden changes in network conditions, a property that currently existing algorithms do not satisfy. We ran tests on real traces and compared the 2W-FD to state-of-the-art algorithms. Our results show that our algorithm presents the best performance in terms of speed and accuracy in unstable scenarios

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Non-Monotonic Snapshot Isolation (NMSI), a variant of the widely deployed Snapshot Isolation (SI), aims at improving scalability by relaxing snapshots. In contrast to SI, NMSI snapshots are causally consistent, which allows for more parallelism and a reduced abort rate. This work documents the design of PhysiCS-NMSI, a transactional protocol implementing NMSI in a partitioned data store. It is the first protocol to rely on a single scalar taken from a physical clock for tracking causal dependencies and building causally consistent snapshots. Its commit protocol ensures atomicity and the absence of write-write conflicts. We argue that PhysiCS-NMSI approach increases concurrency and reduces abort rate and metadata overhead as compared to state-of-art systems.