SQL Server优化器原来的搜索空间就很大,引入data movement(DMS)算子后,进一步增大了。除非query非常简单,否则原有的枚举算法已经不太适用了。本节,论文描述了一种bottom-up的搜索策略。目前,PDW QO使用了bottom-up的搜索策略,top-down的剪枝技术。伪代码如下: PWDOptimizer方法对应于图2步骤4的QueryOptimizer: 将SQL ...
(c)在单机SQL Server中完成单机优化,形成Final (Serial) Memo,传递给PDW optimizer,枚举Shuffle/Replicate等算子,生成Augmented (Parallel) Memo。 (d)从c的Parallel Memo中选出最优分布式计划 (e)转换为DSQL的plan描述,其中包括DMS operation + SQL operation... 总结 SQL Server PDW的并行优化方案还是非常优雅的...
Query Optimizer inside the SQL Server Parallel Data Warehouse product (PDW QO). We leverage existing QO technology in Microsoft SQL Server to implement a cost-based optimizer for distributed query execution. By properly abstracting metadata we can readily reuse existing logic for query simplification,...
Summary: Microsoft SQL Server 2008 collects statistical information about indexes and column data stored in the database. These statistics are used by the SQL Server query optimizer to choose the most efficient plan for retrieving or updating data. This paper describes what data is collected, where...
In SQL Server 2016 we have introduced a number of new Query Optimizer improvements. This article summarizes some them and explains you can leverage the benefits of the new enhancements. Expect deep dive follow up articles for some of the enhancements. Here is the short list: ...
The query optimizer in SQL Server is cost-based. This means that it selects query plans that have the lowest estimated processing cost to execute. The query optimizer determines the cost of executing a query plan based on two main factors: ...
What's New for Statistics in SQL Server 2005? SQL Server 2005 has a number of new statistics features that allow the query optimizer to choose better query plans for a broader range of queries, or otherwise improve the management of statistics. These include the following enhancements: ...
SQL Server内置的查询优化器负责对一个给定的SQL语句执行判断作出最合理的查询计划。因为查询优化器并没有过多的内容展示于外界,因此不像SQL引擎 中的其他组件那样为人熟知。第八章(The Query Optimizer)主要介绍查询优化器及其工原理,本章读完后,你应该会加深在较高层次的优化架构的理解,并熟知一个特定的查询计划为...
3. If updating the stats and fixing the parameter sniffing doesn’t resolve the issue it is more likely optimizer is not able to create efficient plan because of lack of indexes and correct statistics. Run the query which is driving the CPU in database tuning advisor and apply the recommenda...
正确性是说生成的查询计划对标原sql,能不能保证结果集的正确性;有效性是说,对原sql执行RBO+CBO变换后,得到的执行计划是不是高效的。 这篇论文描述了测试查询优化器时遇到的一些独特问题,概述了验证微软SQL Server的查询优化器的测试技术,给出了优化器测试过程中的成功经验和教训,最后讨论了测试器测试中持续存在的...