139273
Applications-driven parallel I/O
The authors investigate the needs of some massively parallel applications running on distributed-memory parallel computers at Argonne National Laboratory and identify some common parallel I/O operations. For these operations, routines were developed that hide the details of the actual implementation (such as the number of parallel disks) from the application, while providing good performance. An important feature is the ability for the application programmer to specify that a file be accessed either as a high-performance parallel file or as a conventional Unix file, simply by changing the value of a parameter on the file open call. These routines are examples of a parallel I/O abstraction that can enhance development, portability, and performance of I/O operations in applications. Some of the specific issues in their design and implementation in a distributed-memory toolset are discussed.
9657478
Computational Electromagnetics and Parallel Dense Matrix Computations
We present computational results using CORAL, a parallel, three-dimensional, nonlinear magnetostatic code based on a volume integral equation formulation. A key feature of CORAL is the ability to solve, in parallel, the large, dense systems of linear equations that are inherent in the use of integral equation methods. Using the Chameleon and PSLES libraries ensures portability and access to the latest linear algebra solution technology.
16053840
Parallel computation of three-dimensional nonlinear magnetostatic problems
We describe a general-purpose parallel electromagnetic code for computing accurate solutions to large computationally demanding, 3D, nonlinear magnetostatic problems. The code, CORAL, is based on a volume integral equation formulation. Using an IBM SP parallel computer and iterative solution methods, we successfully solved the dense linear systems inherent in such formulations. A key component of our work was the use of the PETSc library, which provides parallel portability and access to the latest linear algebra solution technology.
38463254
Locating and Ranking XML Documents Based on Content and Structure Synopses
We present a new framework for indexing, locating and ranking XML documents based on content and structural synopses extracted from the documents. Instead of indexing each single element or term in a document, we extract a structural summary and a small number of data synopses from the document, which are indexed in an efficient way suitable for query evaluation. Our query language is XPath extended with full-text search. The result of query evaluation is a ranked list of document locations that best match the query. We propose a novel aggregated ranking scheme, which is integrated into the query evaluation to score the documents based on those data synopses. Our experimental evaluation shows that our indexing scheme outperforms the standard XML indexing scheme based on inverted lists and our ranking scheme is effective in terms of precision and recall.
17053048
Performance Testing of a Parallel Multiblock CFD Solver
A distributed-memory version of the OVERFLOW computational fluid dynamics code was evaluated on several parallel systems and compared with other approaches using test cases provided by the NASA-Boeing High-Speed Civil Transport program. A principal goal was to develop partitioning and load-balancing strategies that led to a reduction in computation time. We found multipartitioning, in which the aspect ratio of the multipartition is close to the aspect ratio of the grid zone, offered the best performance. The (uniprocessor) performance of the CRAY vector systems was superior to all other systems tested. However, the distributed-memory version when run on an SGI Origin system offers a price performance advantage over the CRAY vector systems.Performance on personal computer systems is promising but faces several hurdles.
15495414
A tool based methodology for development of automatically scalable and reusable parallel code
Program performance may be improved by efficiently programming some key sections of the software. We present a methodology for converting selected portions of source code into automatically scalable multithreaded routines, without forcing programmers to concentrate on parallel programming issues. These developed routines can be reused across various projects, operating systems and system architectures. To support this methodology two separate but tightly coupled tools have been developed -PARSA/sup (TM)/ software development environment (SDE) and the ThreadMan/sup (TM)/ thread manager. The SDE addresses programming issues by allowing a graphical object based approach to develop multithreaded routines that abstracts the users from parallel programming. ThreadMan manages the software developed using SDE. ThreadMan is a user-level thread manager that automatically spawns and schedules threads at runtime. Two examples have been developed using this methodology to demonstrate that there is virtually no degradation in performance when compared to sequential code, in a single processor system and scalability is achieved as the number of processors is increased.
6198667
CABOB: A Fast Optimal Algorithm for Combinatorial Auctions
Combinatorial auctions where bidders can bid on bundles of items can lead to more economical allocations, but determining the winners is NP-complete and inapproximable. We present CABOB, a sophisticated search algorithm for the problem. It uses decomposition techniques, upper and lower bounding (also across components), elaborate and dynamically chosen bid ordering heuristics, and a host of structural observations. Experiments against CPLEX 7.0 show that CABOB is usually faster, never drastically slower, and in many cases drastically faster. We also uncover interesting aspects of the problem itself. First, the problems with short bids that were hard for the first-generation of specialized algorithms are easy. Second, almost all of the CATS distributions are easy, and become easier with more bids. Third, we test a number of random restart strategies, and show that they do not help on this problem because the run-time distribution does not have a heavy tail (at least not for CABOB).
11997775
XML Query Routing in Structured P2P Systems
This paper addresses the problem of data placement, indexing, and querying large XML data repositories distributed over an existing P2P service infrastructure. Our architecture scales gracefully to the network and data sizes, is fully distributed, fault tolerant and self-organizing, and handles complex queries efficiently, even those queries that use full-text search. Our framework for indexing distributed XML data is based on both meta-data information and textual content. We introduce a novel data synopsis structure to summarize text that correlates textual with positional information and increases query routing precision. Our processing framework maps an XML query with full-text search into a distributed program that migrates from peer to peer, collecting relevant document locations along the way. In addition, we introduce methods to handle network updates, such as node arrivals, departures, and failures. Finally, we report on a prototype implementation, which is used to validate the accuracy of our data synopses and to analyze the various costs involved in indexing XML data and answering queries.