137. Your database instance is currently configured to support 1,500 connections. The Web application
that uses the database allows a large number of users to work with the database simultaneously. Some
users of the Web application do not interact with the server all the time.
You want to increase the scalability by configuring the database instance to handle more connections. As
a DBA, which configuration would you set to support more than 1,500 connections at a time?
A.You would configure more listeners for the database.
B.You would configure the database in shared server mode to use the connection pooling feature.
C.You would increase the value of the PGA_AGGREGATE_TARGET initialization parameter that assigns
more session memory to users.
D.You would decrease the value of the PRIVATE_SGA resource limit in the profiles used by the users to
accommodate more session information.
Answer: B
答案解析：
共享服务器连接是一种在程序编写的时候通常会用到的连接池(pool)的概念。采用这种模式的话，在数据库的初始化的时候就会创建一批服务器连接的进程，然后把这些连接进程放入一个连接池来进行管理。初始化的池中的进程数量在数据库初始化建立的时候是可以手动设置的。在连接建立的时候，Listener首先接受到客户端的建立连接的请求，然后Listener去生成一个叫做调度器(dipatcher)的进程与客户端进行连接。调度器把把客户端的请求放在SGA(系统全局域)的一个请求队列中，然后再共享服务器连接池中查找有无空闲的连接，然后让这个空闲的服务器进行处理。处理完毕以后再把处理结果放在SGA的相应队列中。调度器通过查询相应队列，得到返回结果，再返回给客户端。这种连接模式的优点在于服务器进程的数量可以得到控制，不大可能出现因为连接人数过多而造成服务器内存崩溃。但是由于增加了复杂度以及请求相应队列，可能性能上有所下降。