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042-096

原创 Linux操作系统 作者:jbymy2000 时间:2012-03-15 04:16:35 0 删除 编辑
96. Which statement is true when you run the SQL Tuning Advisor with limited scope?
A) Access path analysis is not performed for the SQL statements.
B) SQL structure analysis is not performed for the SQL statements.
C) SQL Profile recommendations are not generated for the SQL statements.
D) The staleness and absence of the statistics are not checked for the objects in the query supplied to the SQL Tuning Advisor.
答案:C
如果选中“Limited(有限制)”选项,SQL 优化指导会根据统计信息检查、访问路径分析和 SQL 结构分析来生成建议案。
使用“Limited(限制)”选项不会生成SQL 概要文件建议(SQL Profile recommendations)。
SQL 概要文件:ATO 会验证它自身的估计值并收集辅助信息以消除估计错误。它使用辅助信息构建SQL 概要文件并提出创建SQL 概要文件的建议。创建 SQL 概要文件后,查询优化程序可使用这个文件生成合理优化的计划。
Editor’s notes:You can see the detail explaination of sql tuning advisor inb12411- 12 Automatic SQL Tuning
SQL Tuning Advisor provides options to manage the scope and duration of a tuning task. The scope of a tuning task can be set to limited or comprehensive.
If the limited option is chosen, the SQL Tuning Advisor produces recommendations based on statistics checks, access path analysis, and SQL structure analysis. SQL Profile recommendations are not generated.
If the comprehensive option is selected, the SQL Tuning Advisor carries out all the analysis it performs under limited scope plus SQL Profiling. With the comprehensive option you can also specify a time limit for the tuning task, which by default is 30 minutes.
dbms_sqltune.create_tuning_task (
sql_text => l_sql,user_name => 'SYS',scope => 'COMPREHENSIVE',
time_limit => 120,task_name => 'TEST');

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