Serveur d'applications

Résumé

vignette|Logo symbolisant une application serveur Un serveur d'applications est un logiciel d'infrastructure offrant un contexte d'exécution pour des composants applicatifs. Le terme est apparu dans le domaine des applications web. Au sens strict les composants hébergés par le serveur d'applications ne sont pas de simples procédures ou scripts mais de réels composants logiciels conformes à un modèle de composants (EJB, COM, Fractal, etc.). Les clients des serveurs d'application sont : des programmes autonomes (standalone application), des applets ou d'autres composants. La structuration en couches des différents composants mis à disposition par le serveur d'application permet une prise en compte des besoins métier, des interactions avec les utilisateurs, des connexions avec les bases de données, etc. Les serveurs d'applications sont des logiciels occupant la couche centrale dans une architecture multicouche, qu'elle soit classique trois tiers (postes clients, serveur d'applications,

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Séances de cours associées (12)

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Caching Dynamic Web Content in J2EE Applications: An Automated Solution Using Aspect Programming

Sumit Mittal, Willy Zwaenepoel

Caching is an effective means for reducing load on web servers, especially for those that dynamically generate web documents in J2EE applications. While adding caching to the application server can greatly reduce response times for requests, the logic to ensure consistency with the backend database requires considerable effort to develop. Much of the complexity is in minimizing unnecessary page invalidations, a key goal for improving the cache hit rate and response times. In this paper we explore a range of invalidation policies that are progressively more precise. A contribution of this work is in achieving precise invalidations at the application server layer automatically. To explore these issues, we introduce AutoWebCache, a system for adding caching for dynamic content automatically to J2EE server-side applications having a back-end database. It uses aspect oriented programming for injecting the cache code automatically into an application, but this method requires the SQL query analysis-- needed for invalidation-- be performed at run-time, which is costly. We demonstrate how to eliminate this run-time analysis overhead through effective caching of intermediate analysis results. In two e-commerce benchmarks, RUBiS and TPC-W, we show our method can be highly effective, reducing the response times, 63% and 97%, respectively.

2004

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Using Code Transformation for Consistent and Transparent Caching of Dynamic Web Content

Sumit Mittal, Willy Zwaenepoel

We present a consistent and transparent caching system for dynamic web pages produced by a server-side application using a back-end database. Cached pages always reflect current database values. No intervention from the programmer is necessary to implement caching. The system is an improvement on earlier methods that either did not guarantee consistency and/or relied on substantial programmer intervention. The novel idea is that a compiler analyzes and transforms the server-side application code to include cache checks, inserts, and invalidations. In order to provide precise invalidations and attendant good hit ratios, we check the intersection of the database table columns used by the read and the write queries, augmented by uniqueness information from the database schema and comparison of the query selection predicates against values inserted in the database. We use Java bytecode rewriting to implement the transformation of the server-side application. Using the Rubis benchmark, we demonstrate that transparent and consistent caching achieves substantial improvements in response time and throughput.

2003

Chargement

C-JDBC: Flexible Database Clustering Middleware

Emmanuel Cecchet, Willy Zwaenepoel

Large web or e-commerce sites are frequently hosted on clusters. Successful open-source tools exist for clustering the front tiers of such sites (web servers and application servers). No comparable success has been achieved for scaling the backend databases. An expensive SMP machine is required if the database tier becomes the bottleneck. The few tools that exist for clustering databases are often database-specific and/or proprietary. Clustered JDBC (C-JDBC) addresses this problem. It is a freely available, open-source, flexible and efficient middleware for database clustering. C-JDBC presents a single virtual database to the application through the JDBC interface. It does not require any modification to JDBC-based applications. It furthermore works with any database engine that provides a JDBC driver, without modification to the database engine. The flexible architecture of C-JDBC supports large and complex database cluster architectures offering various performance, fault tolerance and availability tradeoffs. We present the design and the implementation of C-JDBC, as well as some uses of the system in various scenarios. Finally, performance measurements using a clustered implementation of the TPC-W benchmark show the efficiency and scalability of C-JDBC.

2004

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