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The Domus architecture for distributed hash tables (DHTs) is specially designed to support the concurrent deployment of multiple and heterogeneous DHTs, in a dynamic shared-all cluster environment. The execution model is compatible with the simultaneous access of several distributed/parallel client applications to the same or different running DHTs. Support to distributed routing and storage is dynamically...
The e-commerce Web sites receive a great and varied number of visitors every day. These visitors share the application server's limited resources and when there are too many clients connecting to the Web site, it is possible that they hinder between them, even to overload the application server. These visitors can be divided in different categories, depending on their importance from site viewpoint...
Grid computing technologies are mature enough to be successfully applied to computationally intensive scientific applications. However, the current process of applying grid computing to them is still hard and difficult for the least experienced users. In this paper we describe the adaptations made to the GMarte metascheduling framework in order to provide an ubiquitous access to its functionality...
This paper presents a programming language for parallel computing based on code annotations. It has similar goals and philosophy as OpenMP but it is more tightly coupled to the object oriented paradigm. We include annotations for most common concurrency patterns and mechanisms, namely, one-way, futures, barriers, reads/writers and thread-local. Our current prototype is implemented using Java 5 annotations...
As the complexity of parallel file systems' software stacks increases it gets harder to reveal the reasons for performance bottlenecks in these software layers. This paper introduces a method which eliminates the influence of the physical storage on performance analysis in order to find these bottlenecks. Also, the influence of the hardware components on the performance is modeled to estimate the...
Overlay networks are a fascinating field in the area of distributed systems. They combine challenges from self-organisation to extreme scalability and provide an interesting middleware layer for server-free Internet applications. The design aspects of their implementations, however, remained largely at the prototype level, which renders their integration and deployment in real applications hard. This...
In this paper we propose a Markovian model of BitTorrent. Unlike already developed works which capture demographic dynamics, it focuses on the behavior of individual peers. To this end, we center our attention on a generic peer, called tagged peer (TP); for each possible logical state of a BT peer-to-peer connection maintained by the TP, we consider a stochastic process which counts the number of...
We present an algorithm to compute the cycle structure of large directed graphs where each node has exactly one outgoing edge. Such graphs appear as state diagrams of finite state machines such as pseudorandom number generators in cryptography. The size of the graphs necessitates that the adjacency list is kept on hard disks. Our algorithm uses multiple processing units, so that a parallel storage...
This paper presents multiple-phase collective I/O, a novel collective I/O technique for distributed memory multiprocessors. Multiple-phase collective I/O is a refinement of two-phase collective I/O technique. The communication phase is structured into several steps, which progressively increase the locality of the data to be written to a file system. Besides the description of multiple-phase collective...
Computer modeling and simulation efforts are most useful when they can provide an optimal solution to a problem. Toward this goal we need a vertical hierarchy of algorithmic capabilities and software tools, all of which must work together to make optimal solutions possible. In this presentation we discuss efforts in the Trilinos project to enable optimal solutions for scientific and engineering applications...
Scientific and engineering programming has been around since the beginning of computing, often being the driving force for new system development and innovation. At the same time a continual focus on new modeling capabilities, and some apparent cultural issues, find software processes for many computational science and engineering (CSE) software projects lacking. Certainly there are notable exceptions,...
The branch and bound (B&B) algorithm is one of the most used methods to solve in an exact way combinatorial optimization problems. This article focuses on the multi-objective version of this algorithm, and proposes a new parallel approach adapted to grid computing systems. This approach addresses several issues related to the characteristics of the algorithm itself and the properties of grid computing...
The paper presents a study of medium and coarse grain numerical computations in a new cluster-based shared memory parallel architecture oriented into implementation in "Systems on Chip" (SoC) technology. The assumed architecture is based on dynamic processor clusters, organized around shared memory modules. Fast shared data transfers between processors from different clusters are performed...
Composition of Web services is of great interest to support business-to-business collaboration and provide value added services with desired properties or capabilities. Nevertheless, the standard languages used to create business processes from composite Web services lack of formal definition of their semantics and tools to support the analysis of a business process. In this paper we provide a practical...
The running times of large-scale computational science and engineering parallel applications, executed on clusters or grid platforms, are usually longer than the mean-time-between-failures (MTBF). Hardware failures must be tolerated by the parallel applications to ensure that no all computation done is lost on machine failures. Checkpointing and rollback recovery is a very useful technique to implement...
Due to the network technology advances, an order-of-magnitude jump has been produced in the network bandwidth. This fact has reawake the interest in protocol offloading (particularly in protocols such as TCP, that require a lot of CPU resources to process the stack), since network communication is one key factor for the system performance. Nevertheless, there are controversial studies on protocol...
In this paper we describe an accelerator based on FPGA technology and interfaced to an external host computing system through standard bus connections; it is conceived to accelerate double precision floating point operations, present in the energy calculation of Monte Carlo (MC) metropolis particle system simulations. The accelerator plays the role of coprocessor giving a speed-up factor equal to...
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