A mechanism is provided for generating statistical information for query optimization in a data processing system. The mechanism comprises a first database engine maintaining a current first dataset currently being stored, a second database engine maintaining a second dataset. The second dataset is ...
What is Query Optimization? Query Optimization is a crucial aspect of database management systems (DBMS) that seeks to determine the most efficient way to execute a given query by considering a variety of query execution strategies. The goal is to minimize the system resources required to fulfill...
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...
P. Gassner, G. M. Lohman and K. B. Schiefer, Query Optimization in IBM's DB2 Family of DBMSs,IEEE Data Engineering Bulletin, 16(4), December 1993. G. Graefe, The Cascades Framework for Query Optimization,Bulletin of the Technical Committee on Data Engineering, Vol 18 No. 3, September ...
G.M. Lohman, “Grammar-Like Functional Rules for Representing Query Optimization Alternatives,” Proceedings of the ACM SIGMOD Conference, pp. 18–27 (June 1988). Google Scholar D. Maier, J. Stein, A. Otis, and A. Purdy, “Development of an Object-Oriented DBMS,” Proceedings of the AC...
The introduction of objects extended the supported datatypes and functions. The Extensible Indexing feature discussed in the previous chapter, introduces user-defined access methods. See Also: Oracle9i Database Concepts for an introduction to optimization Oracle9i Database Performance Guide and Reference...
9.对这个最优plan应用post-optimization rules,论文没有给出这个rules是什么,个人理解可能是topN之类的规则。 10.以bottom-up方式生成DSQL 11.对DSQL应用post-DSQL-generation rules 12.返回最终DSQL执行计划 Cost Model PDW优化器的代价评估模型中计算了data movement算子的代价。 Cost Model假设 从0开始建立代价评...
//find the best plan for a group with certain context O_GROUP::perform(context) { If(lower bound of the group greater than upper bound in the context) return; // impossible goal If(there is a winner for the context) Return; // done, no further optimization needed // else, more sear...
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 ...
mpp query optimization 一Query 1 Parsing 代码语言:javascript 代码运行次数:0 运行 AI代码解释 ParserQueryparser(end,settings.enable_debug_queries);ASTPtr ast;//把Query转化为抽象语法树ast=parseQuery(parser,begin,end,"",max_query_size); ASTPtrtryParseQuery(){//Token为lexer词法分析后的基本单位,...