A Scalable Middleware Solution for Advanced Wide Area Web Services

To alleviate scalability problems in the Web, many researchers concentrate on how to incorporate advanced caching and replication techniques. Many solutions incorporate object-based techniques. In particular, Web resources are considered as distributed objects offering a well-defined interface. We argue that most proposals ignore two important aspects. First, there is little discussion on what kind of coherence should be provided. Proposing specific caching or replication solutions makes sense only if we know what coherence model they should implement. Second, most proposals treat all Web resources alike. Such a one-size-fits-all approach will never work in a wide-area system. We propose a solution in which Web resources are encapsulated in physically distributed shared objects. Each object should encapsulate not only state and operations, but also the policy by which its state is distributed, cached, replicated, migrated, etc

Loadable Smart Proxies and Native-Code Shipping for CORBA

Middleware platforms such as CORBA are widely considered as a promising technology path towards a universal service market. For now, however, no mechanisms are offered for dynamically integrating service-specific code (so-called smart proxies) at the client which is a major prerequisite for the development of generic clients that may connect to different service implementations offering different quality-of-service guarantees. In this paper, we therefore demonstrate how support for smart proxies can be integrated within CORBA by means of a native-code shipping service that only relies on the recent objects-by-value extension and portable-interceptors proposal. The feasibility of this approach is shown by a smart-proxy supported video service

A Generic Language for Dynamic Adaptation

International audienceToday, component oriented middlewares are used to design, develop and deploy distributed applications easily. They ensure the heterogeneity, interoperability, and reuse of software modules.Several standards address this issue: CCM (CORBA Component Model), EJB (Enterprise Java Beans) and .Net. However they offer a limited and fixed number of system services, and their deployment and configuration mechanisms cannot be used by any language nor API dynamically.As a solution, we present a generic high-level language to adapt system services dynamically in existing middlewares. This solution is based on a highly adaptable platform which enforces adaptive behaviours, and offers a means to specify and adapt system services dynamically. A first prototype was achieved for the OpenCCM platform, and good performances were obtained

Using Object Replication for Building a Dependable Version Control System

Abstract. Object-oriented technologies are frequently used to design and implement distributed applications. Object replication is a well-established approach to increase the dependability for such applications. Generic replication infrastructures often fail to meet non-standard application-specific requirements such as support for client-side computing. Our FTflex replication infrastructure combines the fragmented object model with semantic annotations in order to customize and optimize replication mechanisms, and thus provides a more flexible replication infrastructure. This paper presents DiGit, a replicated version control system based on the architecture of Git. DiGit is implemented with the help of the FTflex infrastructure for object replication. The contributions of this paper are twofold. First, the paper evaluates the fitness of our replication framework for a specific, complex application. We identify two advantages of the replication infrastructure: the ability to provide client-side code as a conceptually integral part of a remote service, and support for an optimized protocol for remote interaction. As a second contribution, the paper presents a powerful replicated version control system and shows the lessons learned from using object replication in such a system.

Fault-Tolerant Replication Based on Fragmented Objects

This paper describes a novel approach to fault-tolerance in distributed object-based systems. It uses the fragmented-object model to integrate replication mechanisms into distributed applications. This approach enables the use of customised code on a per-object basis to access replica groups and to manage consistency. The addition of fault tolerance to the infrastructure has only little overhead, is fully transparent for clients, and does not require internal modifications to the existing middleware. Semantic annotations at the interface level allow the developer to customise the provision of fault tolerance. Operations can be marked as read-only to allow an execution with weaker ordering semantics or as parallelisable to allow true multithreaded execution. A code-generation tool is provided to automatically produce object-specific fragment code for client access and for replica consistency management, taking into account the annotations, the interface specification, and the non-replicated implementation. A further contribution of our code-generation approach is the support of deterministic multithreading in replicated objects

Saperlipopette!: a Distributed Web Caching Systems Evaluation Tool

Designing a distributed cache infrastructure to improve the Web performance for the users of a large-scale organization is a difficult task. To guide the decisions of system administrators, we propose Saperlipopette!, a tool that can be used to evaluate, a-priori, the quality of the service offered by each potential configuration of the distributed cache infrastructure. Saperlipopette! is based on trace-driven simulations. Our methodology is two-fold. First, we monitor the targeted organizations' Web related activity. Second, we replay the organization's access pattern while simulating the distributed Web support infrastructure. This paper presents the information gathering as well as the design of the tool. We show that beyond a certain cache's size, the performance stays constant whereas the consistency continues to decrease. We also evaluated a number of distributed configurations, among which peer-to-peer Relais cooperation proved to be the best one. Keywords Web caches, configur..