Catálogo de publicaciones - libros

Meanwhile production Grids are robust and reliable Grid systems they are not able to progress as fast as Grid research would enable it and they do not grow as fast as they were originally expected. The remedy for the first problem could be the introduction of volunteer services that can extend production Grids with new services based on the latest Grid research results. Solution for the second problem could be the extension of production Grids with volunteer Grid sites deploying either the same or different Grid middleware used by the production Grid. Advance Grid portal service is a good example for the volunteer Grid services. Combining it with other volunteer services like legacy code service, brokering, monitoring it can even help in solving the second problem by enabling the adoption of volunteer Grid sites without compromising the robustness of the core production Grid. The acceptance of the volunteer service and site concept can contribute to the long term sustainability of production Grids.

Data grid replication is critical for improving the performance of data intensive applications. Most of the used techniques for data replication use Replica Location Services (RLS) to resolve the logical name of files to its physical locations. An example of such service is Giggle, which can be found in the OGSA/Globus architecture. Classical algorithms also need some catalog and optimization services. For example, the EGEE DataGrid project, based in Globus open source components, implements for this purpose the Replica Optimization Service (ROS) and the Replica Metadata Catalog (RMC). In this paper we propose a new approach for improving the performance of Data grid replication. With this aim, we apply Emergent Artificial Intelligence (EAI) techniques to data replication. The paper describes a new algorithm for replica selection in grid environments based on a PSO-LRU (Particle Swarm Optimization) approach. For evaluating this technique we have implemented a grid simulator called SiCoGrid. The simulation results presented in the paper demonstrate that the new technique improve the performance compared with traditional solutions.

This paper presents ModRunner, a scientific model execution manager running on a Grid platform. ModRunner is part of the MODENA environment. Besides model execution, MODENA also deals with knowledge management in scientific models. It also works as a model library allowing for cataloguing, searching, reusing and generating scientific models. ModRunner is a simple and effective Grid Computing access system that facilitates management of independent task execution on the Grid. In this paper, we present ModRunner running over the Grid Computing middleware OurGrid. As a case study we have been using ModRunner to schedule, submit and manage tasks for the execution of Population Dynamics models.

Relaxing replica freshness has been exploited in database clusters to optimize load balancing. However, in most approaches, refreshment is typically coupled with other functions such as routing or scheduling, which makes it hard to analyze the impact of the refresh strategy itself on performance. In this paper, we propose to support routing-independent refresh strategies in a database cluster with mono-master lazy replication. First, we propose a model for capturing existing refresh strategies. Second, we describe the support of this model in Refresco, a middleware prototype for freshness-aware routing in database clusters. Third, we describe an experimental validation to test some typical strategies against different workloads. The results show that the choice of the best strategy depends not only on the workload, but also on the conflict rate between transactions and queries and on the level of freshness required by queries. Although there is no strategy that is best in all cases, we found that one strategy is usually very good and could be used as default strategy.

Data visualization is important in the context of grid applications, especially when successive refinements are iteratively realized based on intermediate results. We mainly focus on code coupling grid applications, structured as a set of distributed, autonomous, weakly-coupled codes. We consider the case where the codes are able to interact using the abstraction of a shared data space. In previous work, we have proposed an efficient visualization scheme by introducing a new operation called , as an extension to the model. This operation can efficiently take place without locking, in parallel with operations. On the other hand, the user has to relax the consistency constraints, and accept slightly older versions of the data, whose “freshness” can however still be controlled. In this paper, we discuss and extensively evaluate the proposed consistency protocol, whose efficiency is clearly demonstrated by our experimental results.

Many scientific experiments deal with data-intensive applications and the orchestration of computational workflow activities. These can benefit from data parallelism exploited in parallel systems to minimize execution time. Due to its complexity, robustness and efficiency to exploit data parallelism, grid infrastructures are widely used in some e-Science areas like bioinformatics. Workflow techniques are very important to bioinformatics experiments, allowing the e-scientist to describe and enact experimental process in a structured, repeatable and verifiable way. The main purpose of this paper is to describe our experience with Tavena Workbench and PeDRo, which are part of Grid project. Taverna is provided with a workflow toolset and enactor, allowing the specification of processing units, data transfer and execution constraints. As a data entry tool, PeDRo provides a model, a controlled vocabulary and field validations for Web Services descriptions, leveraging the knowledge associated to the workflows. The main contribution of this work is a summary of some considerations drawn by our experience with the use of these tools, emphasizing its advantages and negative aspects, together with proposals for some future improvements.