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首页> 外文会议>British National Conference on Databases(BNCOD 23); 20060718-23; Belfast(GB) >On the Optimal Ordering of Maps, Selections, and Joins Under Factorization
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On the Optimal Ordering of Maps, Selections, and Joins Under Factorization

机译：分解条件下映射，选择和联接的最优排序

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摘要

We examine the problem of producing the optimal evaluation order for queries containing joins, selections, and maps. Specifically, we look at the case where common subexpressions involving expensive UDF calls can be factored out. First, we show that ignoring factorization during optimization can lead to plans that are far off the best possible plan: the difference in cost between the best plan considering factorization and the best plan not considering factorization can easily reach several orders of magnitude. Then, we introduce optimization strategies that produce optimal left-deep and bushy plans when factorization is taken into account. Experiments (1) confirm that factorization is a critical issue when it comes to generating optimal plans and (2) we show that to consider factorization does not make plan generation significantly more expensive.
机译：我们研究了为包含联接，选择和映射的查询生成最佳评估顺序的问题。具体来说，我们看一下可以排除涉及昂贵的UDF调用的常见子表达式的情况。首先，我们表明在优化过程中忽略因式分解会导致计划与最佳方案相去甚远：考虑因式分解的最佳计划与不考虑因式分解的最佳计划之间的成本差异很容易达到几个数量级。然后，我们引入了优化策略，当考虑到因式分解时，该策略可产生最佳的左深和浓密计划。实验（1）确认分解对于生成最佳计划而言是一个关键问题，并且（2）我们表明考虑分解不会使计划的生成变得更加昂贵。

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