Oracle Database 11 g - Online Public Access Catalog

140 CHAPTER 3 ■ DATABASE ADMINISTRATIONthe dedicated server, the connection is maintained for the lifetime of the connection, wastingcrucial memory resources in the bargain.By enabling resource sharing among middle-tier client applications, you can now scale upto a large number of user connections with a much smaller resource usage.How DRCP WorksWhen you use a dedicated server, the instance creates a new server process in response to anew client connection request, along with a new client session. Under DRCP, a connectionbroker assigns the new client connection to a pooled server, if one is already available. Theclient connection will release the pooled server back to the connection pool once its request isserviced by the database. In both the dedicated server and shared server methods, the clientconnection releases the memory and other resources back to the instance only after the terminationof the session.If the connection broker can’t find an available free pooled server to assign to the newclient connection, it will create a new pooled server. However, if the number of pooled serversis at the maximum level, the connection broker won’t be able to create a new pooled server.The client connection will have to go into a wait queue until an existing pooled server is releasedback to the connection pool by the client connections that are using the available pooled servers.Both the dedicated server method and the DRCP method allocate memory from the programglobal area (PGA). However, the big advantage of using the DRCP method lies in the fact thatthe memory requirement is proportional to the number of active pooled servers in the connectionpool, and not to the number of client connections, as is the case under the dedicated serverapproach. Here’s an example that shows the tremendous gains you can achieve in memoryusage by switching to DRCP from traditional dedicated server connections.Let’s say there are 10,000 client connections, with each client session requiring 200KB ofmemory and each server process requiring 5MB. Let’s assume that the maximum number ofpooled servers is 200. Here are the total requirements for a dedicated server approach and thenew DRCP method:Dedicated serverTotal memory required = 10000 X (200KB + 5MB) = 520GBDatabase Resident Connection PoolingTotal Memory Required = 200 X (200KB + 5MB) = 1.04 GBShared Server1000 X 200KB + 200 X 5MB = 21GBYou can see that DRCP requires only a little more than 1GB of memory for the 10,000 users,whereas the dedicated server approach will require a mammoth 520GB of memory!■Note You can’t shut down the database after connecting through a pooled server. You also can’t useencryption and certificates or connect to a connection pool on a different instance through a database link.