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Abstract. We consider the use of a database cluster for Application Service Provider (ASP). In the ASP context, applications and databases can be update-intensive and must remain autonomous. In this paper, we describe the Leganet system which performs freshness-aware transaction routing in a database cluster. We use multi-master replication and relaxed replica freshness to increase load balancing. Our transaction routing takes into account freshness requirements of queries at the relation level and uses a cost function that takes into account the cluster load and the cost to refresh replicas to the required level. We implemented the Leganet prototype on a 11-node Linux cluster running Oracle8i. Using experimentation and emulation up to 128 nodes, our validation based on the TPC-C benchmark demonstrates the performance benefits of our approach.

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ABSTRACT. We consider the use of a cluster system for Application Service Provider (ASP

Abstract. Grid systems provide access to huge storage and computing resources at large scale. While they have been mainly dedicated to scientific computing for years, grids are now considered as a viable solution for hosting data-intensive applications. To this end, databases are replicated over the grid in order to achieve high availability and fast transaction processing thanks to parallelism. However, achieving both fast and consistent data access on such architectures is challenging at many points. In particular, centralized control is prohibited because of its vulnerability and lack of efficiency at large scale. In this article, we propose a novel solution for the distributed control of transaction routing in a large scale network. We leverage a cluster-oriented routing solution with a fully distributed approach that uses a large scale distributed directory to handle routing metadata. Moreover, we demonstrate the feasibility of our implementation through experimentation: results expose linear scale-up, and transaction routing time is fast enough to make our solution eligible for update intensive applications such as world wide online booking.

We consider the use of a cluster system for managing autonomous databases. In order to improve the performance of read-only queries, we strive to exploit user requirements on replica freshness. Assuming mono-master lazy replication, we propose a freshness model to help specifying the required freshness level for queries. We propose an algorithm to optimize the routing of queries on slave nodes based on the freshness requirements. Our approach uses non intrusive techniques that preserve application and database autonomy. We provide an experimental validation based on our prototype Refresco. The results show that freshness control can help increase query throughput significantly. They also show significant improvement when freshness requirements are specified at the relation level rather than at the database level.

Abstract. Nowadays, many applications are interested in detecting and discovering changes on the web to help users to understand page updates and more generally, the web dynamics. Web archiving is one of these fields where detecting changes on web pages is important. Archiving institutes are collecting and preserving different web site versions for future generation. A major problem encountered by archiving systems is to understand what happened between two versions of web pages. In this paper, we address this requirement by proposing a new change detection approach that computes the semantic differences between two versions of HTML web pages. Our approach, called Vi-DIFF, detects changes on the visual representation of web pages. It detects two types of changes: content and structural changes. Content changes include modifications on text, hyperlinks and images. In contrast, structural changes alter the visual appearance of the page and the structure of its blocks. Our Vi-DIFF solution can serve for various applications such as crawl optimization, archive maintenance, web changes browsing, etc. Experiments on Vi-DIFF were conducted and the results are promising.

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