Serveur web

Résumé

vignette|Serveurs de la Wikimedia Foundation. Un serveur web est soit un logiciel de service de ressources web (serveur HTTP), soit un serveur informatique (ordinateur) qui répond à des requêtes du World Wide Web sur un réseau public (Internet) ou privé (intranet), en utilisant principalement le protocole HTTP. Un serveur informatique peut être utilisé à la fois pour servir des ressources du Web et pour faire fonctionner en parallèle d'autres services liés, comme l'envoi de courriers électroniques, l'émission de flux en streaming, le stockage de données dans des bases de données, le transfert de fichiers par . Présentation Les serveurs web publics sont reliés à Internet et hébergent des ressources (pages web, images, vidéos) du Web. Ces ressources peuvent être statiques (servies telle quelles) ou dynamiques (construites à la demande par le serveur). Certains serveurs sont seulement accessibles sur des réseaux privés (intranets) et hébergent des sites

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The mean-field behavior of processor sharing systems with general job lengths under the SQ(d) policy

Arpan Mukhopadhyay

This paper addresses the mean-field behavior of large-scale systems of parallel servers with a processor sharing service discipline when arrivals are Poisson and jobs have general service time distributions when an SQ(d) routing policy is used. Under this policy, an arrival is routed to the server with the least number of progressing jobs among d randomly chosen servers. The limit of the empirical distribution is then used to study the statistical properties of the system. In particular, this shows that in the limit as N grows, individual servers are statistically independent of others (propagation of chaos) and more importantly, the equilibrium point of the mean-field is insensitive to the job length distributions that has important engineering relevance for the robustness of such routing policies used in web server farms. We use a framework of measure-valued processes and martingale techniques to obtain our results. We also provide numerical results to support our analysis. (C) 2018 Elsevier B.V. All rights reserved.

ELSEVIER SCIENCE BV2018

Chargement

This thesis introduces a new implementation of the LAIO api, liblaiogen. LAIO stands for Lazy Asynchronous I/O. It is an api for performing asynchronous I/O. Among several benefits, one of the most important is that LAIO is lazy, in the sense that it creates a continuation only when an operation actually blocks. LAIO was introduced along with an implementation for FreeBSD using scheduler activations to provide this lazy characteristic. Our objective is to provide a cross-platform implementation. To achieve this, liblaiogen uses threads eagerly instead of relying on scheduler activations to save threads for non blocking operations. By doing this we challenge the argument that kernel threads are inherently expensive, which is the justification for the need of a mechanism such as scheduler activa- tions. We compare the performances of liblaiogen in the scope of event- driven web servers, using the same web server and the same benchmark that was used to benchmark the original FreeBSD implementation of LAIO. We show that on recent versions of Linux with lightweight threading sup- port, the web server using liblaiogen performs better than the one using LAIO on FreeBSD. We highlight the different component of the operating system that are responsible for the differences in performance.

2005

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Cooperative Data Exchange and Private Information Retrieval

Su Li

Coding techniques have been well studied and used for improving communication quality by combating noise and mitigating interference. Recently, it has been shown that the same coding techniques can also be exploited to further improve communication performance and provide specific communication features even when the communication channel is ideal. In this thesis, we study two problems where coding techniques are used for improving communications in distributed systems and protecting the privacy of the client from untrusted servers, respectively.\ The first part of this thesis studies the cooperative data exchange problem for fully connected networks. While many previous studies have shown that the problem can be solved by algorithms based on submodular function minimization, we tackle this problem via a concept we refer to as "conditioning basis", which is closely linked to linear coding schemes with particular additional properties. We show that such special linear coding schemes are optimal for the cooperative data exchange problem. Hence, by searching the existence of such a conditioning basis and special linear coding schemes, we can solve this problem with lower complexity. We propose a deterministic algorithm for this problem and briefly show how to construct the optimal linear coding schemes starting from a Vandermonde matrix. Moreover, we show that our new method can be used to solve two generalized problems, which are cooperative data exchange with weighted cost and successive local omniscience problems.\ The second part of this thesis investigates the problem of private information retrieval with side information. Specifically, three different extensions are studied: multi-message, multi-server, and multi-user, respectively. For each problem, we provide a proof of the converse for the download rate as well as propose efficient approaches to construct optimal coding schemes. For multi-message and multi-server cases, we give closed-form expressions for the download rates and introduce two useful tools, {\it conditioning answer string} and {\it virtual private information}, to analyze the problem. For multi-user cases, we show that the optimal download rate can be obtained by solving an optimization problem over all partitions of the total number of messages and propose a novel algorithm based on dynamic programming to solve the optimization problem.\

EPFL2020

Chargement

Cooperative Data Exchange and Private Information Retrieval

Su Li

EPFL2020