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RAC Workload ManagementA new feature is Real Application Clusters Guard II. Real Application Clusters Guard II supports comprehensive workload management to maintain high availability for Real Application Clusters databases and their applications. Real Application Clusters Guard II transfers application load based on the concept of service names. Therefore, Real Application Clusters Guard II supports workload management based on service levels, as well as applications using database services. Service names now support high availability because you do not have to make application changes to implement them. In Oracle9i, service names replace the old sid names used in previous releases in the tnsnames.ora file and in the listener.ora files. The database can now register with the listener process, providing the listener with the service names, instance names, and network addresses of the database, as well as the current state and load of all instances and shared server dispatchers. With this information, the listener can forward client connection requests to the appropriate dispatchers and dedicated servers, depending on the setting of load balancing options in the tnsnames.ora file. In addition, service names provide location transparency to the database instances that offer the service. Service names enable a single-system image that simplifies the configuration, operation, and recovery of workloads. The benefits of Oracle9i RAC are many. The major benefits are scalability, high availability, and transparency. Let's discuss each in the following sections. RAC ScalabilityOracle9i RAC offers nearly linear scalability, meaning that you can continue to add servers indefinitely to keep up with processing demands. Tests performed by companies such as Compaq, SUN, HP, DELL, and Intel all confirm that Oracle9i RAC scales nearly linearly. Figure 4.5 shows example results for scalability tests using Intel 4 way servers with Intel Xeon processors. Figure 4.5: Example Oracle9i RAC Scalability (Data From: Deploying Oracle9i Real Application Clusters on Intel Architecture-based Servers, Rick Jacobson, Intel, 2002) The results in Figure 4.5 mirror the test results from all other companies. The scalability for Oracle9i RAC usually runs at a minimum 1.9 scalability ratio (this means that for 2 servers you get 1.9 times the transactions possible on 1 server). Tests performed by PolyServe and XIOTech, documented in "The Tens: Creating a Very Large Database On Intel-Based Servers with Oracle9i Real Applications Clusters," illustrated clusters using 10 - Intel based servers running Linux served up 10 terabytes of data to over 5000 users with an average response time of less than 3 seconds. On HPUX using 4 - HP N-class servers with 8-550 Mhz CPUs and 32 GB RAM each, a scaling factor for all four nodes was 3.76 (this means that if you did 100 QPS on a single node you could do 376 QPS on a 4-node cluster), an almost linear scalability. This is shown in Figure 4.6. Figure 4.6: HPUX RAC Scale Factor and Queries per Second As you can see, whether it is measured by a scaling factor or by queries per second, Oracle9i RAC gives true scalability to an application. What about high availability? Let's examine that in the next section. High AvailabilityPerformance issues aside, the major reason for utilizing Oracle9i RAC is high availability. If one node in an Oracle9i RAC cluster fails, the other nodes pick up the load. There are multiple options that can be utilized with Oracle9i RAC to ensure nearly seamless failover in the event of node or instance failure. These configuration options for high availability will be discussed in detail in the chapters that follow. TransparencyOracle9i RAC is the first parallel server Oracle database system that provides true transparency for applications. COTS software that runs on Oracle9i can be placed on an Oracle9i RAC cluster with no changes. This application transparency is due to Oracle9i cache fusion technology. Once the application killers such as true and false pinging were eliminated, application transparency was achieved. For more information, see the book Oracle 11g Grid and Real Application Clusters - 30% off if you buy it directly from Rampant TechPress . Written by top Oracle experts, this RAC book has a complete online code depot with ready to use RAC scripts.
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