【OCP最新题库解析(052)--题29】 For which requirement should you config

Q

题目

For which requirement should you configure shared servers?

A. accommodating an increasing number of users who run short-duration, infrequent queries in an OLTP environment with limited memory.

B. using Recovery Manager(RMAN) to recover a database.

C. submitting backup jobs at regular, 24-hour intervals in an OLTP environment with limited memory.

D. accommodating an increasing number of users who run analytical queries in a DSS environment with limited memory.

E. performing bulk-load operations in a DSS environment with limited memory.

A

答案

Answer：A

使用连接共享功能，数据库服务器可以使空闲会话超时，从而使用其连接为活动会话提供服务。空闲会话逻辑上仍处于打开状态，当该会话下次发出请求时会自动重新建立物理连接。因此，Web应用程序可使用现有硬件来满足大量并发用户的需求。连接共享是通过共享服务器进行配置的。

Oracle共享服务器体系结构是一个有效的进程和内存使用模型，但是并不适用于所有的连接。由于存在公共请求队列，并且大量用户会共享分派程序响应队列，所以当存在必须处理大批数据的操作时共享服务器的性能并不是很好，如处理仓库查询或执行批处理时。使用Oracle Recovery Manager进行备份和恢复会话时，也会处理大量的数据集，因此也必须使用专用连接。

许多管理任务不能（无法）使用共享服务器连接执行，其中包括启动和关闭实例、创建表空间和数据文件、维护索引和表、分析统计信息，以及通常由DBA执行的其它多个任务。

所有DBA会话都必须选择专用服务器。

Using shared servers reduces the number of processes and the amount of memory consumed on the database host. Shared servers are beneficial for databases where there are many OLTP users performing intermittent transactions.

Using shared servers rather than dedicated servers is also generally better for systems that have a high connection rate to the database. With shared servers, when a connect request is received, a dispatcher is available to handle concurrent connection requests. With dedicated servers, however, a connection-specific dedicated server is sequentially initialized for each connection request.

Performance of certain database features can improve when a shared server architecture is used, and performance of certain database features can degrade slightly when a shared server architecture is used. For example, a session can be prevented from migrating to another shared server while parallel execution is active.

A session can remain nonmigratable even after a request from the client has been processed, because not all the user information has been stored in the UGA. If a server were to process the request from the client, then the part of the user state that was not stored in the UGA would be inaccessible. To avoid this situation, individual shared servers often need to remain bound to a user session.