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Auflistung nach Schlagwort "Query optimization"

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  • Zeitschriftenartikel
    Placement-Safe Operator-Graph Changes in Distributed Heterogeneous Data Stream Systems
    (Datenbank-Spektrum: Vol. 15, No. 3, 2015) Pollner, Niko; Steudtner, Christian; Meyer-Wegener, Klaus
    Data stream processing systems enable querying continuous data without first storing it. Data stream queries may combine data from distributed data sources like different sensors in an environmental sensing application. This suggests distributed query processing. Thus the amount of transferred data can be reduced and more processing resources are available.However, distributed query processing on probably heterogeneous platforms complicates query optimization. This article investigates query optimization through operator graph changes and its interaction with operator placement on heterogeneous distributed systems. Pre-placement operator graph changes may prevent certain operator placements. Thereby the resource consumption of the query execution may unexpectedly increase. Based on the operator placement problem modeled as a task assignment problem (TAP), we prove that it is NP-hard to decide in general whether an arbitrary operator graph change may negatively influence the best possible TAP solution. We present conditions for several specific operator graph changes that guarantee to preserve the best possible TAP solution.
  • Zeitschriftenartikel
    Speculative Dynamic Reconfiguration and Table Prefetching Using Query Look-Ahead in the ReProVide Near-Data-Processing System
    (Datenbank-Spektrum: Vol. 21, No. 1, 2021) Beena Gopalakrishnan, Lekshmi; Becher, Andreas; Wildermann, Stefan; Meyer-Wegener, Klaus; Teich, Jürgen
    FPGAs are promising target architectures for hardware acceleration of database query processing, as they combine the performance of hardware with the programmability of software. In particular, they are partially reconfigurable at runtime, which allows for the runtime adaptation to a variety of queries. However, reconfiguration costs some time, and a region of the FPGA is not available for computations during its reconfiguration. Techniques to avoid or at least hide the reconfiguration latencies can improve the overall performance. This paper presents optimizations based on query look-ahead, which follows the idea of exploiting knowledge about subsequent queries for scheduling the reconfigurations such that their overhead is minimized. We evaluate our optimizations with a calibrated model for various parameter settings. Improvements in execution time can be “calculated” even if only being able to look one query ahead.
  • Zeitschriftenartikel
    Unleashing XQuery for Data-Independent Programming
    (Datenbank-Spektrum: Vol. 14, No. 2, 2014) Bächle, Sebastian; Sauer, Caetano
    The XQuery language was initially developed as an SQL equivalent for XML data, but its roots in functional programming make it also a perfect choice for processing almost any kind of structured and semi-structured data. Apart from standard XML processing, however, advanced language features make it hard to efficiently implement the complete language for large data volumes. This work proposes a novel compilation strategy that provides both flexibility and efficiency to unleash XQuery’s potential as data programming language. It combines the simplicity and versatility of a storage-independent data abstraction with the scalability advantages of set-oriented processing. Expensive iterative sections in a query are unrolled to a pipeline of relational-style operators, which is open for optimized join processing, index use, and parallelization. The remaining aspects of the language are processed in a standard fashion, yet can be compiled anytime to more efficient native operations of the actual runtime environment. This hybrid compilation mechanism yields an efficient and highly flexible query engine that is able to drive any computation from simple XML transformation to complex data analysis, even on non-XML data. Experiments with our prototype and state-of-the-art competitors in classic XML query processing and business analytics over relational data attest the generality and efficiency of the design.