Oracle Database 11 g - Online Public Access Catalog

CHAPTER 3 ■ DATABASE ADMINISTRATION 139Using Restore Points for Creating Archival BackupsIn Oracle Database 11g, you can use restore points during the implementation of archivalbackups. We explain archival backups in Chapter 6.Database Resident Connection PoolingTraditionally, Oracle offered you two different types of server processes, which handle therequests of use processes. These are the dedicated server process, which handles one userprocess at a time, and the shared server process, which serves multiple user processes simultaneouslythrough dispatchers. By default, an Oracle database always allows a dedicated serverprocess, but the shared server process needs special configuration. Shared server processesoffer an efficient way to scale up when faced with large numbers of user connections by eliminatingthe need to start a dedicated server for each user connection.It’s common for web-based client applications that have similar database credentials andthat use identical schema to share or reuse sessions. Huge numbers of client connections alsomean memory requirements become a problem if connections and scalability of the middletier and database tiers are an issue. Web-based applications aren’t always “active” throughouta session. Rather, they show bursts of activity, and they don’t maintain state through the timethey are connected to the database. You can use database connection pooling so a small numberof database sessions can service a large number of end users, increasing both performance andscalability. However, technologies such as PHP can’t take advantage of connection pooling viathe application server, since they require a separate database connection for each web serverprocess. Even if an application can use application-server-level connection pooling, it will stillbe stymied by a high number of database connections when dealing with large numbers ofapplication servers.In Oracle Database 11g, you can configure scarce resources even better in a large-userenvironment by using the new database resident connection pooling (DRCP) feature. DRCPemploys a pool of dedicated servers for servicing larger numbers of connections and is capableof handling tens of thousands of simultaneous connections to the database while using verylittle memory when compared to both a dedicated server and a shared server approach. Applicationsthat currently can’t avail of application server connection pooling, as well as applicationsthat run on large application server farms, can take advantage of this feature to increase scalability.DRCP is especially designed to help architectures that use multiprocess, single-threadedapplication servers (PHP with Apache, for example) that are incapable of middle-tier connectionpooling. Using DRCP, these applications can now effortlessly scale to tens of thousands ofsimultaneous connections.DRCP is similar to the traditional dedicated server connection model, which is the defaultmethod of connection to an Oracle database but doesn’t need an exclusive dedicated server foreach user connection throughout the lifetime of the connection. The server in DRCP works justlike the dedicated server while the user connection is actually working with it, but is referred toas a pooled server. The pooled servers combine an Oracle server process and user session, justas a dedicated server does. The server is a pooled server rather than a dedicated server, becauseeach connection acquires a server for a temporary period from a pool of servers. When the userconnection is done using the database, it relinquishes the server connection back to the serverpool. In a dedicated server connection method, on the other hand, the server connection isterminated only after the client connection is terminated. So, even if a client isn’t actively using