Modélisation et contrôle de la performance et de la disponibilité des systèmes de serveurs Les serveurs informatiques permettent de mettre en œuvre un large éventail de services en ligne et d'applications telles que les services Web, les services de messagerie ou les services de base de données. Cependant, leur configuration ad hoc soulève des problématiques cruciales liées à la performance, la disponibilité et le coût économique des applications. Dans cette thèse, nous étudions l'impact de la configuration des serveurs sur le compromis central entre performance et disponibilité du service. Dans une première partie, nous modélisons le comportement de serveurs uniques à l'aide d'approximations fluides et développons des lois de commandes novatrices pour le contrôle d'admission sur les systèmes de serveurs centralisés. Nous proposons plusieurs lois de commande pour différentes combinaisons d'objectifs de qualité de service et de niveau de service. Parmi elles, AM-C garantit un objectif de performance du service en maximisant sa disponibilité; PM-C garantit un objectif de disponibilité du service en maximisant sa performance. Nous évaluons expérimentalement le modèle ainsi que les stratégies de contrôle sur TPC-C, un benchmark industriel reconnu qui reproduit un service d'e-commerce, implémenté sur le serveur de base de données PostgreSQL. Nos expériences montrent que les techniques proposées améliorent jusqu'à 30% les performances du service tout en garantissant les contraintes de disponibilité. Dans une deuxième partie, nous étendons ce travail aux systèmes de serveurs distribués, qui sont largement utilisés par les applications Internet évoluant sur des systèmes multi-niveaux hébergés par des clusters de serveurs. Nous présentons un modèle de serveur distribué comme un modèle continu non linéaire en faisant une analogie avec les systèmes transferts de fluide. Nous formalisons alors un problème d'optimisation pour le contrôle de ces systèmes. Nous fournissons un contrôle d'admission qui permet d'obtenir la disponibilité de service la plus élevée tout en garantissant un objectif de performance. Une évaluation numérique du modèle proposé et du contrôle distribué associé est présentée et montre que la configuration optimale de ces systèmes n'est pas intuitive.

Server technology provides a means to support a wide range of online services and applications. However, their ad hoc configuration poses significant challenges to the performance, availability, and economical costs of applications. In this paper, we examine the impact of server configuration on the central trade-off between service performance and availability. First, we present a server model as a nonlinear continuous-time model using fluid approximations. Second, we develop concurrency control on server systems for an optimal configuration. We primarily provide two control laws for two different QoS objectives. AM-C is an availability-maximizing server control that achieves the highest service availability given a fixed performance constraint; and PM-C is a performance-maximizing control law that meets a desired availability target with the highest performance. We then improve the control with two additional multilevel laws. AA-PM-C is an availability-aware performance-maximizing control, and PA-AM-C is a performance-aware availability-maximizing control. In this paper, we present ConSer, a novel system for the control of servers. We evaluate ConSer's fluid model and control techniques on the TPC-C industry-standard benchmark. Our experiments show that the proposed techniques successfully guarantee performance and availability constraints.

Multi-tier architectures are widely used by internet applications. Guaranteeing the performance, and more generally the quality of service (QoS), of such applications remains a crucial issue. In this paper we propose a methodology to get the optimal admission control of multi-tier server systems under high loads for one QoS objective. First we present a model of multi-tier server systems using fluid approximations. Second, we state and solve an optimization problem which consists in finding the configuration that maximizes the availability of the system for a given performance constraint. Simulations of both model and control from this preliminary work are presented. They show that the optimal configuration of such systems is not always intuitive.

Servers technology is a mean to support different Internet services and applications ranging from web servers, to email systems, streaming media services, enterprise servers, and database servers. However, the ad-hoc configuration of servers poses significant challenges to the performance and economical costs of applications. This paper precisely addresses this issue. Firstly, we present the design of a server model as a non-linear continuous-time model. A fluid flow approach allows us to partly free ourselves from accurate stochastic considerations. Secondly, a utility function for characterizing the impact of server configuration on performance and cost is presented. Thirdly, a utility-aware capacity planning algorithm is developed to efficiently control the configuration of servers. Model and control algorithm were implemented and applied to the standard PostgreSQL database server running the TPC-C warehouse application. The experiments show that the proposed method provides significant benefits for database servers management.

Dans cet article nous etudions l'influence de la configuration d'un serveur sur les aspects antinomiques de performance et de disponibilite du service. Dans un premier temps nous presentons un modele de serveur construit a partir d'approximations de type fluide. Ensuite nous developpons deux lois de controle d'admission qui visent a optimiser la configuration du serveur afin de respecter deux objectifs de QoS. Le premier objectif consiste a maximiser la disponibilite de service tout en garantissant une contrainte sur sa performance. Le second consiste a maximiser la performance du service tout en garantissant une contrainte sur sa disponibilite. Le modele et les lois de commandes sont evaluees experimentalement sur le banc d'essai TPC-C.

Although server technology provides a means to support a wide range of online services and applications, their ad-hoc configuration poses significant challenges to the performance, availability and economical costs of applications. In this paper, we examine the impact of server configuration on the central tradeoff between service performance and availability. First, we present a server model as a nonlinear continuous-time model using fluid approximations. Second, we develop admission control of server systems for an optimal configuration. We provide two control laws for two different QoS objectives. AM-C is an availability-maximizing admission control that achieves the highest service availability given a fixed performance constraint; and PM-C is a performance-maximizing admission control that meets a desired availability target with the highest performance. We evaluate our fluid model and control techniques on the TPC-C industry-standard benchmark. Our experiments show that the proposed techniques improve performance by up to 30 % while guaranteeing availability constraints.

Although server technology provides a mean to support a wide range of online services and applications, their ad-hoc configuration poses significant challenges to the performance, availability and economical costs of applications. One of the main concerns is that under a heavy load, the delay introduced by a server in the transaction process may grow unbounded. This paper precisely addresses this issue. First, we present the design of a server model as a non-linear continuous-time model. Second, we develop an admission control algorithm that allow to ensure a maximum average delay on the server. Model and control algorithm were implemented and applied on the standard PostgreSQL database server running the TPC-C warehouse application. The experiments show that the proposed method provides significant benefits for database servers management.