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,...
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: Compatibility Le...
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: ...
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...
The distribution of data across tables affects execution plans. Uneven data distribution can lead to suboptimal plan choices, resulting in slow query performance. 4. Query Complexity The complexity of a query influences the optimizer's plan selection. Complex queries may hav...
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: ...
优化器(Optimizer) 优化器 解决“怎么做”问题的工具就是“优化器”。优化器也称查询优化器(Query Optimizer)【注意这里的“查询”并不仅仅指Select操作,包括Select,Update,Delete,Insert等等在内的任何带WHERE条件子句的SQL操作都包含查询操作的】。它的主要工作是优化数据访问,根据提交的SQL语句,综合各种已有的信息(主...
SQL Plan Management SQL plan management is a mechanism that enables the optimizer to automatically manage execution plans, ensuring that the database uses only known or verified plans. In SQL plan management, the optimizer has the following main objectives: ...