The West Encounters And Transformations Volume 2 Pdf' title='The West Encounters And Transformations Volume 2 Pdf' />Introduction to the Optimizer. This chapter discusses SQL processing, optimization methods, and how the optimizer chooses a specific plan to execute SQL. The chapter contains the following sections Overview of SQL Processing. SQL processing uses the following main components to execute a SQL query The Parser checks both syntax and semantic analysis. TEXTBOOK MAKING PHYSICS FUN KEY CONCEPTS CLASSROOM ACTIVITIES AND EVERYDAY EXAMPLES GRADES K 8 PDF EBOOKS advice for great cvs negotiating environment and science an. Issuu is a digital publishing platform that makes it simple to publish magazines, catalogs, newspapers, books, and more online. Easily share your publications and get. TEXTBOOK SUCH A SIMPLE LITTLE TALE SUCH A SIMPLE LITTLE TALE PDF EBOOKS card template for animals citroen c25 manual summary of short stories aqa anthology. 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The Optimizer uses costing methods, cost based optimizer CBO, or internal rules, rule based optimizer RBO, to determine the most efficient way of producing the result of the query. The Row Source Generator receives the optimal plan from the optimizer and outputs the execution plan for the SQL statement. The SQL Execution Engine operates on the execution plan associated with a SQL statement and then produces the results of the query. Figure 1 1 illustrates SQL processing. Figure 1 1 SQL Processing Overview. Text description of the illustration pfgrf. Overview of the Optimizer. The optimizer determines the most efficient way to execute a SQL statement after considering many factors related to the objects referenced and the conditions specified in the query. This determination is an important step in the processing of any SQL statement and can greatly affect execution time. A SQL statement can be executed in many different ways, including the following Full table scans. Index scans. Nested loops. Hash joins. Note The optimizer might not make the same decisions from one version of Oracle to the next. Best-Ideas-of-50-Essays-Pdf-With-Free-Download--1024x576.jpg' alt='The West Encounters And Transformations Volume 2 Pdf' title='The West Encounters And Transformations Volume 2 Pdf' />In recent versions, the optimizer might make different decisions, because better information is available. The output from the optimizer is a plan that describes an optimum method of execution. The Oracle server provides the cost based CBO and rule based RBO optimization. In general, use the cost based approach. Oracle Corporation is continually improving the CBO and new features require CBO. Note Oracle Corporation strongly advises the use of cost based optimization. The rule based optimization is available for backward compatibility with legacy applications and will be deprecated in a future release. You can influence the optimizers choices by setting the optimizer approach and goal, and by gathering representative statistics for the CBO. The optimizer goal is either throughput or response time. See Choosing an Optimizer Approach and Goal. Sometimes, the application designer, who has more information about a particular applications data than is available to the optimizer, can choose a more effective way to execute a SQL statement. The application designer can use hints in SQL statements to specify how the statement should be executed. Features that Require the CBOThe following features require use of the CBO Partitioned tables and indexes. Index organized tables. Reverse key indexes. Function based indexes. SAMPLE clauses in a SELECT statement. Parallel query and parallel DMLStar transformations and star joins. Extensible optimizer. Query rewrite with materialized views. Enterprise Manager progress meter. Hash joins. Bitmap indexes and bitmap join indexes. Index skip scans. Note Using any of these features enables the CBO, even if the parameter OPTIMIZERMODE is set to RULE. Optimizer Operations. For any SQL statement processed by Oracle, the optimizer performs the operations listed in Table 1 1. Table 1 1  Optimizer Operations. Choosing an Optimizer Approach and Goal. By default, the goal of the CBO is the best throughput. This means that it chooses the least amount of resources necessary to process all rows accessed by the statement. Oracle can also optimize a statement with the goal of best response time. This means that it uses the least amount of resources necessary to process the first row accessed by a SQL statement. The execution plan produced by the optimizer can vary depending on the optimizers goal. Optimizing for best throughput is more likely to result in a full table scan rather than an index scan, or a sort merge join rather than a nested loop join. Optimizing for best response time usually results in an index scan or a nested loop join. For example, suppose you have a join statement that can be executed with either a nested loops operation or a sort merge operation. The sort merge operation might return the entire query result faster, while the nested loops operation might return the first row faster. If your goal is to improve throughput, then the optimizer is more likely to choose a sort merge join. If your goal is to improve response time, then the optimizer is more likely to choose a nested loop join. Choose a goal for the optimizer based on the needs of your application For applications performed in batch, such as Oracle Reports applications, optimize for best throughput. Usually, throughput is more important in batch applications, because the user initiating the application is only concerned with the time necessary for the application to complete. Response time is less important, because the user does not examine the results of individual statements while the application is running. For interactive applications, such as Oracle Forms applications or SQLPlus queries, optimize for best response time. Usually, response time is important in interactive applications, because the interactive user is waiting to see the first row or first few rows accessed by the statement. The optimizers behavior when choosing an optimization approach and goal for a SQL statement is affected by the following factors OPTIMIZERMODE Initialization Parameter. The OPTIMIZERMODE initialization parameter establishes the default behavior for choosing an optimization approach for the instance. The possible values and description are listed in Table 1 2. Table 1 2  OPTIMIZERMODE Parameter Values. Value. Description. CHOOSEThe optimizer chooses between a cost based approach and a rule based approach, depending on whether statistics are available. This is the default value. Install Perl Module On Red Hat Linux Version'>Install Perl Module On Red Hat Linux Version. If the data dictionary contains statistics for at least one of the accessed tables, then the optimizer uses a cost based approach and optimizes with a goal of best throughput. If the data dictionary contains only some statistics, then the cost based approach is still used, but the optimizer must guess the statistics for the subjects without any statistics. This can result in suboptimal execution plans. If the data dictionary contains no statistics for any of the accessed tables, then the optimizer uses a rule based approach. ALLROWSThe optimizer uses a cost based approach for all SQL statements in the session regardless of the presence of statistics and optimizes with a goal of best throughput minimum resource use to complete the entire statement. FIRSTROWSn. The optimizer uses a cost based approach, regardless of the presence of statistics, and optimizes with a goal of best response time to return the first n number of rows n can equal 1, 1. FIRSTROWSThe optimizer uses a mix of cost and heuristics to find a best plan for fast delivery of the first few rows. Note Using heuristics sometimes leads the CBO to generate a plan with a cost that is significantly larger than the cost of a plan without applying the heuristic. FIRSTROWS is available for backward compatibility and plan stability. RULEThe optimizer chooses a rule based approach for all SQL statements regardless of the presence of statistics. You can change the goal of the CBO for all SQL statements in a session by changing the parameter value in initialization file or by the ALTERSESSIONSETOPTIMIZERMODE statement. Nokia Sl3 Unlock Server.