Core Grid technologies are rapidly maturing, but there remains a shortage of real Grid applications. One important reason is the lack of a simple and high-level application programming toolkit, bridging the gap between existing Grid middleware and application-level needs. The Grid Application Toolkit (GAT), as currently developed by the EC-funded project GridLab [1], provides this missing functionality. As seen from the application, the GAT provides a unified simple programming interface to the Grid infrastructure, tailored to the needs of Grid application programmers and users. A uniform programming interface will be needed for application developers to create a new generation of "Grid-aware" applications. The GAT implementation handles both the complexity and the variety of existing Grid middleware services via so-called adaptors. Complementing existing Grid middleware, GridLab also provides high-level services to implement the GAT functionality.We present the GridLab software architecture, consisting of the GAT, environment-specific adaptors, and GridLab services. We elaborate the concepts underlying the GAT and outline the corresponding application programming interface. We present the functionality of GridLab's high-level services and demonstrate how a dynamic Grid application can easily benefit from the GAT. All GridLab software is open source and can be downloaded from the project Web site.

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Consistent hashing is at the core of many P2P protocols. It evenly distributes the keys over the nodes, thereby enabling logarithmic routing effort 'with high probability'. However, consistent hashing incurs unnecessary overhead as shown in this paper.By removing consistent hashing from Chord, we derived a protocol that has the same favorable logarithmic routing performance but needs less network hops for updating its routing table. Additionally, our Chord # protocol supports range queries, which are not possible with Chord. Our empirical results indicate that Chord # outperforms Chord even under high churn, that is, when nodes frequently join and leave the system.

SUMMARYWe present a scheme for reserving job resources with imprecise requests. Typical parameters such as the estimated runtime, the start time or the type or number of required CPUs need not be fixed at submission time but can be kept fuzzy in some aspects. Users may specify a list of preferences which guide the system in determining the best matching resources for the given job. Originally, the impetus for our work came from the need for efficient co-reservation mechanisms in the Grid where rigid constraints on multiple job components often make it difficult to find a feasible solution. Our method for handling fuzzy reservation requests gives the users more freedom to specify the requirements and it gives the Grid Reservation Service more flexibility to find optimal solutions. In the future, we will extend our methods to process co-reservations. We evaluated our algorithms with real workload traces from a large supercomputer site. The results indicate that our scheme greatly improves the flexibility of the solution process without having much affect on the overall workload of a site. From a user's perspective, only about 10% of the nonreservation jobs have a longer response time, and from a site administrator's view, the makespan of the original workload is extended by only 8% in the worst case.