An experimental evaluation of the Pastis peer-to-peer file system under churn

Ce papier présente une évaluation exprimentale du système de fichiers Pastis dans un réseau pair-à-pair dynamique. Nous évaluons le comportement de Pastis afin de déterminer sa capacité à s'adapter aux changements du réseau. Nous utilisons une version modifiée de la DHT PAST afin d'améliorer la gestion des données modifiables et la tolérance la volatilité du réseaux, c'est-à-dire, aux connexions et déconnexions des noeuds. Notre protocole de réplication distingue entre les blocs modifiables et immutables, ce qui diminue la probabilité de perte de données. Enfin, un protocole à base de quorums permet d'assurer la cohérence des données modifiables en présence de noeuds fautifs. Nos expérimentations utilisent Modelnet pour émuler les latences d'un réseau large échelle ainsi que la bande passante asyémtrique des clients connectés par des liens ADSL. Les résultats montrent que Pastis permet de conserver la cohérence des données même des taux de volatilitlés

Semantic Middleware for Designing Collaborative Applications in Mobile Environment

International audienceThe Telex middleware facilitates the design of collaborative applications in a mobile environment. It provides optimistic replication, tentative execution and disconnected work. It solves conflicts based on semantic information provided by applications. We study in particular a Shared Calendar (SC) application, whereby mobile users can create and manage meetings in a collection of shared calendars. The application provides Telex with objects representing (1) meeting creation and modification operations (actions), (2) dependence or conflict information between actions (constraints). When a conflict occurs, Telex proposes solutions to users. The advantage of this approach is a clean separation of concerns. The SC application writer concentrates on application logic, whereas Telex takes care of replication, consistency, conflicts, and commitment across all applications

Telex: Principled System Support for Write-Sharing in Collaborative Applications

The Telex system is designed for sharing mutable data in a distributed environment, particularly for collaborative applications. Users operate on their local, persistent replica of shared documents; they can work disconnected and suffer no network latency. The Telex approach to detect and correct conflicts is application independent, based on an action-constraint graph (ACG) that summarises the concurrency semantics of applications. The ACG is stored efficiently in a multilog structure that eliminates contention and is optimised for locality. Telex supports multiple applications and multi-document updates. The Telex system clearly separates system logic (which includes replication, views, undo, security, consistency, conflicts, and commitment) from application logic. An example application is a shared calendar for managing multi-user meetings; the system detects meeting conflicts and resolves them consistently

A Performance Evaluation of a Quorum-Based State-Machine Replication Algorithm for Computing Grids

Quorum systems are well-known tools that improve the performance and the availability of distributed systems. In this report we explore their use as a means to achieve low response time for network services that are replicated and accessed over computing grids. To that end, we propose both a quorum construction and a quorum-based state-machine replication algorithm that tolerates crash failures in a partially synchronous model. We show through the evaluation of a real implementation that although simple, this quorum construction and replication algorithm exhibit a response time 20% lower than that of a regular active replication algorithm in appropriate conditions

Telex: A Semantic Platform for Cooperative Application Development

International audienceDeveloping write-sharing applications is challenging. Remote and offline data sharing are increasingly important. We propose a generic platform called Telex to ease development and to provide guarantees. Telex is driven by application semantics. Telex takes care of replication and persistence, drives application progress, and ensures that replicas eventually agree on a correct, common state. We show by example how application design proceeds from high-level application invariants to application-provided parameters that guides Telex. The main data structure of Telex is a large, replicated, highly dynamic graph; we discuss the engineering trade-offs for such a graph and our solutions. Finally, we report an experimental evaluation of Telex based on a cooperative calendar application and on benchmarks

Idiosyncratic features in tRNAs participating in bacterial cell wall synthesis

The FemXWv aminoacyl transferase of Weissella viridescens initiates the synthesis of the side chain of peptidoglycan precursors by transferring l-Ala from Ala-tRNAAla to UDP-MurNAc-pentadepsipeptide. FemXWv is an attractive target for the development of novel antibiotics, since the side chain is essential for the last cross-linking step of peptidoglycan synthesis. Here, we show that FemXWv is highly specific for incorporation of l-Ala in vivo based on extensive analysis of the structure of peptidoglycan. Comparison of various natural and in vitro-transcribed tRNAs indicated that the specificity of FemXWv depends mainly upon the sequence of the tRNA although additional specificity determinants may include post-transcriptional modifications and recognition of the esterified amino acid. Site-directed mutagenesis identified cytosines in the G1–C72 and G2–C71 base pairs of the acceptor stem as critical for FemXWv activity in agreement with modeling of tRNAAla in the catalytic cavity of the enzyme. In contrast, semi-synthesis of Ala-tRNAAla harboring nucleotide substitutions in the G3–U70 wobble base pair showed that this main identity determinant of alanyl-tRNA synthetase is non-essential for FemXWv. The different modes of recognition of the acceptor stem indicate that specific inhibition of FemXWv could be achieved by targeting the distal portion of tRNAAla for the design of substrate analogues

A Comparison of Optimistic Approaches to Collaborative Editing of Wiki Pages

Wikis, a popular tool for sharing knowledge, are basically collaborative editing systems. However, existing wiki systems offer limited support for co-operative authoring, and they do not scale well, because they are based on a centralised architecture. This paper compares the well-known centralised MediaWiki system with several peer-to-peer approaches to editing of wiki pages: an operational transformation approach (MOT2), a commutativity-oriented approach (WOOTO) and a conflict resolution approach (ACF). We evaluate and compare them, according to a number of qualitative and quantitative metrics

ePOST, une expérience de courrier électronique pair-à-pair

National audienc

Pastis (un système pair à pair de gestion de fichier)

Pastis est un nouveau système de gestion de fichier pair à pair qui se démarque des systèmes existants par son architecture entièrement décentralisée et sa capacité à supporter un grand nombre d'utilisateurs. Pastis s'appuie sur la table de hachage distribuée Past, qui lui fournit ses propriétés d'auto-organisation, de tolérance aux fautes, de disponibilité et de passage à l'échelle. Pastis propose trois modèles de cohérence, permettant aux applications de choisir le compromis adéquat entre performance et cohérence des accès au système de fichiers. Ces modèles tirent parti des propriétés de localité de Past pour optimiser les accès réseau et augmenter les performances du système. Pastis garantit l'intégrité des données en s'appuyant sur des techniques cryptographiques et en implémentant un contrôle d'accès utilisant des ACL partagées. L'évaluation de Pastis en environnement émulé et simulé suggère que ses performances sont comparables ou supérieures à celles des systèmes existants.PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Mathématiques rech (751052111) / SudocSudocFranceF

Pastis : un système de fichiers pair-à-pair multi-écrivain passant l'échelle

National audienc