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How Good are Query Optimizers, Really?

How Good are Query Optimizers, Really?

陈傲天
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Finding a good join order is crucial for query performance. In this paper, we introduce the Join Order Benchmark (JOB) and experimentall revisit the main components in the classic query optimizer architecture using a complex, real-world data set and realistic multi-join queries. We investigate the quality of industrial-strength cardinality estimators and find that all estimators routinely produce large errors. We further show that while estimates are essential for finding a good join order, query performance is unsatisfactory if the query engine relies too heavily on these estimates.
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