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 ...
Relational Algebra Query Optimization in Distributed DBMS - Learn about relational algebra query optimization techniques in distributed database management systems to enhance performance and efficiency.
In a distributed database system, processing a query comprises of optimization at both the global and the local level. The query enters the database system at the client or controlling site. Here, the user is validated, the query is checked, translated, and optimized at a global level....
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...
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 ...
See Also: Oracle9i Database Concepts for an introduction to optimization Oracle9i Database Performance Guide and Reference for information about using hints in SQL statements The extensible optimizer feature allows authors of user-defined functions and indexes to create statistics collection, selectivity...
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- ...
The Query Optimizer 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 conta ...
FIG. 3 schematically illustrates query optimization by a database management system (DBMS). A query100is posed by a client computer12, for example, to the server computer16running database management software. The query100is initially parsed by a parser102which examines the syntax of the query ...
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