Dataflow query execution in a parallel main-memory environment |
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Authors: | Annita N Wilschut Peter M G Apers |
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Affiliation: | (1) University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands;(2) University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands |
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Abstract: | In this paper, the performance and characteristics of the execution of various join-trees on a parallel DBMS are studied. The results of this study are a step into the direction of the design of a query optimization strategy that is fit for parallel execution of complex queries.Among others, synchronization issues are identified to limit the performance gain from parallelism. A new hash-join algorithm is introduced that has fewer synchronization constraints than the known hash-join algorithms. Also, the behavior of individual join operations in a join-tree is studied in a simulation experiment. The results show that the introduced Pipelining hash-join algorithm yields a better performance for multi-join queries. The format of the optimal join-tree appears to depend on the size of the operands of the join: A multi-join between small operands performs best with a bushy schedule; larger operands are better off with a linear schedule. The results from the simulation study are confirmed with an analytic model for dataflow query execution. |
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Keywords: | parallel query processing multi-join queries simulation analytical modeling |
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