Replicating Web Applications On-Demand

Many Web-based commercial services deliver their content using Web applications that generate pages dynamically based on user profiles, request parameters etc. The workload of these applications are often characterized by a large number of unique requests and a significant fraction of data updates. Hosting these applications drives the need for systems that replicates both the application code and its underlying data. We propose the design of such a system that is based on on-demand replication, where data units are replicated only to servers that access them often. This reduces the consistency overhead as updates are sent to a reduced number of servers. The proposed system allows complete replication transparency to the application, thereby allowing developers to build applications unaware of the underlying data replication. We show that the proposed techniques can reduce the client response time by a factor of 5 in comparison to existing techniques for a realworld e-commerce application used in the TPC-W benchmark. Furthermore, we evaluate our strategies for a wide range of workloads and show that on-demand replication performs better than centralized and fully replicated systems by reducing the average latency of read/write data accesses as well as the amount of bandwidth utilized to maintain data consistency. 1

An Architectural Style for Ajax

A new breed of web application, dubbed AJAX, is emerging in response to a limited degree of interactivity in large-grain stateless Web interactions. At the heart of this new approach lies a single page interaction model that facilitates rich interactivity. We have studied and experimented with several AJAX frameworks trying to understand their architectural properties. In this paper, we summarize three of these frameworks and examine their properties and introduce the SPIAR architectural style. We describe the guiding software engineering principles and the constraints chosen to induce the desired properties. The style emphasizes user interface component development, and intermediary delta-communication between client/server components, to improve user interactivity and ease of development. In addition, we use the concepts and principles to discuss various open issues in AJAX frameworks and application development.Comment: 2nd revision: references ordered, images resized, typo

Dash: A Novel Search Engine for Database-Generated Dynamic Web Pages

Office of Research, Singapore Management Universit

Comanche: aplicações web estendidas nos clientes

Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para obtenção do grau de Mestre em Engenharia InformáticaA Internet é uma rede de comunicações que permite a troca de informação entre computadores localizados em qualquer ponto do mundo. Vários serviços foram desenvolvidos utilizando esta rede de comunicações. Entre estes, encontra-se a Web, que permite a qualquer utilizador aceder, utilizando o protocolo HTTP, a documentos hipermédia identificados através de um URL. Com a popularidade da Web, surgiram várias propostas para melhorar o desempenho global da Web e permitir o desenvolvimento de aplicações complexas neste ambiente. Entre estas propostas encontram-se, por exemplo, novas versões do protocolo HTTP, sistemas de caching e replicação e sistemas de suporte à operação desconectada. Neste trabalho apresenta-se o desenho e implementação do sistema Comanche, que permite tratar pedidos HTTP na máquina do cliente, possibilitando a adição de novas funcionalidades sem alteração dos servidores. Esta aproximação permite ainda minimizar o número de pedidos que têm de ser tratados pelos servidores, diminuindo assim a quantidade de pedidos processados e o tráfego na rede. O Comanche é implementado como uma proxy de HTTP, que se encontra instalada na máquina do utilizador e consegue instalar e executar Java Web Applications. Estas aplicações permitem a criação local de respostas a pedidos HTTP. Estas aplicações podem também ser usadas para se adicionar funcionalidades extra, alterando as respostas ou recolhendo informação de valor para o utilizador, que pode ser posteriormente usada para fornecer outros serviços. O sistema permite combinar aplicações de forma a permitir a reutilização das mesmas, formando aplicações mais complexas, e disponibiliza uma funcionalidade de sincronização de recursos acessíveis por HTTP

Scalable hosting of web applications

Modern Web sites have evolved from simple monolithic systems to complex multitiered systems. In contrast to traditional Web sites, these sites do not simply deliver pre-written content but dynamically generate content using (one or more) multi-tiered Web applications. In this thesis, we addressed the question: How to host multi-tiered Web applications in a scalable manner? Scaling up a Web application requires scaling its individual tiers. To this end, various research works have proposed techniques that employ replication or caching solutions at different tiers. However, most of these techniques aim to optimize the performance of individual tiers and not the entire application. A key observation made in our research is that there exists no elixir technique that performs the best for allWeb applications. Effective hosting of a Web application requires careful selection and deployment of several techniques at different tiers. To this end, we present several caching and replication strategies, such as GlobeCBC, GlobeDB and GlobeTP, to improve the scalability of different tiers of a Web application. While these techniques and systems improve the performance of the individual tiers (and eventually the application), an application's administrator is not only interested in the performance of its individual tiers but also in its endto- end performance. To this end, we propose a resource provisioning approach that allows us to choose the best resource configuration for hosting a Web application such that its end-to-end response time can be optimized with minimum usage of resources. The proposed approach is based on an analytical model for multi-tier systems, which allows us to derive expressions for estimating the mean end-to-end response time and its variance.Steen, M.R. van [Promotor]Pierre, G.E.O. [Copromotor