Deterministic, Mutable, and Distributed Record-Replay for Operating Systems and Database Systems

Application record and replay is the ability to record application execution and replay it at a later time. Record-replay has many use cases including diagnosing and debugging applications by capturing and reproducing hard to find bugs, providing transparent application fault tolerance by maintaining a live replica of a running program, and offline instrumentation that would be too costly to run in a production environment. Different record-replay systems may offer different levels of replay faithfulness, the strongest level being deterministic replay which guarantees an identical reenactment of the original execution. Such a guarantee requires capturing all sources of nondeterminism during the recording phase. In the general case, such record-replay systems can dramatically hinder application performance, rendering them unpractical in certain application domains. Furthermore, various use cases are incompatible with strictly replaying the original execution. For example, in a primary-secondary database scenario, the secondary database would be unable to serve additional traffic while being replicated. No record-replay system fit all use cases. This dissertation shows how to make deterministic record-replay fast and efficient, how broadening replay semantics can enable powerful new use cases, and how choosing the right level of abstraction for record-replay can support distributed and heterogeneous database replication with little effort. We explore four record-replay systems with different semantics enabling different use cases. We first present Scribe, an OS-level deterministic record-replay mechanism that support multi-process applications on multi-core systems. One of the main challenge is to record the interaction of threads running on different CPU cores in an efficient manner. Scribe introduces two new lightweight OS mechanisms, rendezvous point and sync points, to efficiently record nondeterministic interactions such as related system calls, signals, and shared memory accesses. Scribe allows the capture and replication of hard to find bugs to facilitate debugging and serves as a solid foundation for our two following systems. We then present RacePro, a process race detection system to improve software correctness. Process races occur when multiple processes access shared operating system resources, such as files, without proper synchronization. Detecting process races is difficult due to the elusive nature of these bugs, and the heterogeneity of frameworks involved in such bugs. RacePro is the first tool to detect such process races. RacePro records application executions in deployed systems, allowing offline race detection by analyzing the previously recorded log. RacePro then replays the application execution and forces the manifestation of detected races to check their effect on the application. Upon failure, RacePro reports potentially harmful races to developers. Third, we present Dora, a mutable record-replay system which allows a recorded execution of an application to be replayed with a modified version of the application. Mutable record-replay provides a number of benefits for reproducing, diagnosing, and fixing software bugs. Given a recording and a modified application, finding a mutable replay is challenging, and undecidable in the general case. Despite the difficulty of the problem, we show a very simple but effective algorithm to search for suitable replays. Lastly, we present Synapse, a heterogeneous database replication system designed for Web applications. Web applications are increasingly built using a service-oriented architecture that integrates services powered by a variety of databases. Often, the same data, needed by multiple services, must be replicated across different databases and kept in sync. Unfortunately, these databases use vendor specific data replication engines which are not compatible with each other. To solve this challenge, Synapse operates at the application level to access a unified data representation through object relational mappers. Additionally, Synapse leverages application semantics to replicate data with good consistency semantics using mechanisms similar to Scribe

Path-Tree Optimization in Partially Observable Environments using Rapidly-Exploring Belief-Space Graphs

Robots often need to solve path planning problems where essential and discrete aspects of the environment are partially observable. This introduces a multi-modality, where the robot must be able to observe and infer the state of its environment. To tackle this problem, we introduce the Path-Tree Optimization (PTO) algorithm which plans a path-tree in belief-space. A path-tree is a tree-like motion with branching points where the robot receives an observation leading to a belief-state update. The robot takes different branches depending on the observation received. The algorithm has three main steps. First, a rapidly-exploring random graph (RRG) on the state space is grown. Second, the RRG is expanded to a belief-space graph by querying the observation model. In a third step, dynamic programming is performed on the belief-space graph to extract a path-tree. The resulting path-tree combines exploration with exploitation i.e. it balances the need for gaining knowledge about the environment with the need for reaching the goal. We demonstrate the algorithm capabilities on navigation and mobile manipulation tasks, and show its advantage over a baseline using a task and motion planning approach (TAMP) both in terms of optimality and runtime.Comment: Also submitted to IROS 2022 and RA-

The transition towards critique: discussing capillary ascension with beginning teachers

International audienceThis investigation focuses on possible links between the development of critical attitude and conceptual understanding among beginning teachers. In eleven in-depth interviews with pre-service teachers, we sought their opinions about the explanatory value of a number of texts on the topic of capillary ascension. The goal was to finely analyse each participant's transition from critical passivity to explicit critique. In processing the transcripts, we followed two lines of analysis, addressing conceptual understanding and critical attitude. Coding of the interviews centred on four main critiques of the texts. The prevalence of " delayed critique "-a long time interval of critical passivity or instability commonly observed for three of the four critical arguments considered a priori-aligns with previous results from studies on radiocarbon dating, survival blanket and osmosis. It also became clear that better comprehension of the phenomenon did not in itself mean that future teachers would critique an inappropriate diagram in current use. This finding suggests that when constructing a critical analysis, participants had difficulty relating a qualitative explanation of the phenomenon to how to model the situation, as confirmed by the triggering effect of a new diagram introduced by the interviewer. The paper concludes by discussing the implications for teachers' formation and for future research

Developing critical thinking in Physics – The apprenticeship of critique

International audienceThis book promotes the effective implementation and development of critical analysis in physics. It focuses on explanatory texts concerning subjects typically dealt with in secondary or higher education and addressed in an academic or popular context. It highlights the general difficulties and obstacles inherent in teaching physics and shows how some tools can help to combine successful criticism and better understanding. The book examines the main reasons to call a text into question and looks at risk factors such as simplifications, story-like explanations and visual analogies. It takes inventory of the benefits and limits of critical analysis and discusses the complex links between conceptual mastery and critical attitude. The book ends by offering tools to activate critical thinking and ways for educators to guide students towards productive critical analysis

Concept et critique : lignes enchevêtrées des dynamiques d'apprentissage en physique

International audience(non présent dans le livre) L'objectif d'attractivité et l'accent mis par les textes officiels sur les compétences, au détriment de la structuration conceptuelle, vont de facto avec une extrême simplification des contenus enseignés et un appauvrissement conceptuel des ressources pédagogiques en circulation. Ce contexte accentue doublement la nécessité de développer une attitude critique chez étudiants et enseignants. Mais peut-on raisonnablement envisager un développement sur ce plan sans assurer une base conceptuelle minimale à ceux que l'on forme? Des éléments de réponse à cette question sont fournis par une série d'études qui mettent en jeu des situations physiques relativement simples. Les enquêtes reposent sur des entretiens approfondis-notamment auprès d'enseignants en fin d'études. Une tentative de cartographie des parcours intellectuels observés fait apparaître des développements conceptuels et critiques imbriqués, et des effets de seuil. Sur cette base, les orientations officielles actuelles et la forme que pourraient prendre des interventions de formation seront discutées

THE ENERGY-ECONOMY-ENVIRONMENT INTERACTION AND THE REBOUND-EFFECT A.P.A. MUSTERS

is the leading institute in the Netherlands for energy research. ECN carries out basic and applied research in the fields of nuclear energy, fossil fuels, renewable energy sources, policy studies, environmental aspects of energy supply and the development and application of new materials. IECN employs more than 900 staff. Contracts are obtained from the government and from national and foreign organizations anti industries. ECN’s research results are published in a number of report series, each series serving a different public, from contractors to the international scientific world. The l-series is for internal reports that contain results mainly of interest for (fellow) colleagues, principally within ECN but also for those employed elsewhere. Although these reports may hot be in their final form, they may be referred to. Het Energieonderzoek Centrum Nederland (ECN) is het centrale instituut voor onderzoek op energie gebied in Nederland. ECN verricht fundamenteel en toegepast onderzoek op het gebied van kernenergie fossiele-energiedragers, duurzame energie, beleids-studies, milieuaspecten van de energievoorziening er de ontwikkeling en toepassing van nieuwe materialen Bij ECN zijn ruim 900 medewerkers werkzaam. D~ opdrachten worden verkregen van de overheid en vaï organisaties en industrieën uit binnen- en buitenland De resultaten van het ECN-onderzoek worden heer. gelegd in diverse rapportenseries, bestemd voor ver schillende doelgroepen, van opdrachtgevers tot d~ internationale wetenschappelijke wereld. De l-serie is de serie interne rapporten die resultater bevat bestemd voor de ECN-collega’s, maar ook voo~ vakcollega’s die elders werkzaam zijn. Deze rapporter hebben een minder definitief karakter, maar zijn we refereerbaar

Critiquing Explanations in Physics: Obstacles and Pedagogical Decisions Among Beginning Teachers

International audienc

L'apprentissage de la critique - Développer l'analyse critique en physique

International audienceVous n’êtes pas toujours satisfait des explications de phénomènes physiques qui vous sont données ? Vous êtes un enseignant cherchant à améliorer ses explications ? Ce livre est fait pour vous. Vous y trouverez des moyens d’informer et de libérer votre esprit critique.À partir de nombreux exemples (siphon, pile, osmose, etc.), les raisons de refuser ou d’émettre un doute sur une explication sont détaillées dans un style clair et accessible. Une méthode pratique d’analyse de textes en est tirée. L’intérêt est d’armer ceux qui veulent apprendre, pour leur éviter d’être induits en erreur, et ceux qui veulent enseigner, pour éclairer leurs choix pédagogiques.Véritable manuel de formation éprouvé avec succès auprès de futurs enseignants, ce livre provient d’une réflexion qui a inspiré des recherches récentes sur le développement de l’attitude critique. Celle-ci apparaît avant tout comme un puissant moteur de réflexion permettant d’améliorer la construction des savoirs scientifiques