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ROX: Run-Time Optimization of XQueries   Riham Abdel Kader

ROX: Run-Time Optimization of XQueries

244 страниц. 2011 год.
LAP Lambert Academic Publishing
Relational query optimizers are not always robust. They depend on statistics and cost models which are often inaccurate, and sometimes absent. They fail to detect correlations, and cannot efficiently handle the large search space of big queries. Those challenges and their impact on the quality of the chosen plan are aggravated in the context of XML. In fact, in XML, it is harder to collect and maintain representative statistics. Moreover, the search space of plans is usually larger than that of relational queries, due to the higher number of joins in a typical XQuery. ROX, our Run-time Optimizer for XQueries, is autonomous, not depending on statistics and cost models, is robust in always finding a good execution plan benefiting from the detected correlations, and is efficient in exploring the space of plans. ROX moves the optimization to run-time, and interleaves it with query execution, defining the plan incrementally. Sampling techniques are used to accurately estimate the...
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