Query processing also includes the execution of this generated QEP. While generating a QEP for a user submitted query the DBMS explores a large number of potential execution alternatives. To choose the best ones among those alternatives requires one or more (query) optimization phases. Historical ...
由于SQL是声明式语言(declarative),用户只告诉了DBMS想要获取什么,但没有指出如何计算。因此,DBMS需要将SQL语句转换成可执行的查询计划(Query Plan)。但是对同样的数据可以有多种查询方案,性能也差距很大,查询优化器(Query Optimizer)的任务就是从给定的查询中选择一个最优的方案。 最早的查询优化器实现是IBM在1970s...
By selecting the optimal execution plan for processing data, Query Optimization significantly improves database performance and minimizes latency. FAQs What is Query Optimization? Query Optimization is an aspect of DBMS that determines the most efficient way to execute a given query. Why is Query Opti...
Query processing refers to the sequence of steps that the DBMS will initiate to process the query. Queries can be broadly divided into two categories: single-scan queries and multiscan queries. In a single-scan query, a record (tuple) in the table (relation) being queried has to be ...
Query optimizationis the process of choosing the most efficient means of executing a SQL statement. SQL is a nonprocedural language, so the optimizer is free to merge, reorganize, and process in any order. The database optimizes each SQL statement based on statistics collected about the accessed...
Transaction Processing Performance Council, TPC Benchmark D (Decision Support) Standard Specification Revision 1.1, December, 1995 R.H.Wolniewicz and G.Graefe, Algebraic Optimization of Computations over Scientific Databases,Proc. Intl’ Conf. On Very Large Data Bases, Dublin, Ireland, August 1993,...
关键词:Query Optimization, Cost Model, MPP, Parallel Processing 前言 大数据带来了对查询优化的新兴兴趣,因为一种新型的数据管理系统在可扩展性、可用性和处理能力方面推动了前所未有的突破(例如,[9,18,20,21]),这使得数百TB甚至PB级别的大型数据集可以通过SQL或类似SQL的接口轻松进行分析。优化器的好坏差异一直...
This chapter discusses SQL processing, optimization methods, and how the query optimizer (usually called the optimizer) chooses a specific plan to execute SQL. The chapter contains the following sections: Overview of the Query Optimizer ...
in DBMSs, and Freytag [Fre87] and Graefe/DeWitt [GD87] have addressed some of the difficulties of extensible query optimization. The difficulty of specifying the repertoire of alternative QEPs in a high-level, declarative manner has prompted Frey- ...
This chapter discusses SQL processing, optimization methods, and how the query optimizer (usually called the optimizer) chooses a specific plan to execute SQL.The chapter contains the following sections:Overview of the Query Optimizer Overview of Optimizer Access Paths Overview of Joins Reading ...