|Oracle® Real Application Clusters Deployment and Performance Guide
10g Release 1 (10.1)
Part Number B10768-02
This chapter discusses topics for deploying online (OLTP), data warehouse, and general purpose (hybrid) applications in Oracle Real Application Clusters (RAC) environments. The topics in this chapter are:
All single-instance application development and deployment techniques apply to RAC. If your applications run well on a single-instance Oracle database, then they will run well on a RAC database.
High availability in the event of failures
Scalability to accommodate increased system demands
Load balancing according to demand fluctuations
The high availability features of Oracle and RAC can re-distribute and load balance workloads to surviving instances without interrupting processing. RAC also provides excellent scalability so that if you add or replace a node, then Oracle re-masters resources and re-distributes processing loads.
To accommodate the frequently changing workloads of online transaction processing systems, RAC remains flexible and dynamic despite changes in system load and system availability. RAC addresses a wide range of service levels that, for example, fluctuate due to:
Varying user demands
Peak scalability issues like trading storms (bursts of high volumes of transactions)
Varying availability of system resources
This section discusses how to deploy data warehouse systems in RAC environments by briefly describing the data warehouse features available in shared disk architectures. The topics in this section are:
RAC is ideal for data warehouse applications because it augments the single instance benefits of Oracle. RAC does this by maximizing the processing available on all of the nodes that belong to a RAC database to provide speed-up for data warehouse systems.
The query optimizer considers parallel execution when determining the optimal execution plans. The default cost model for the query optimizer is CPU+I/O and the cost unit is time. In RAC, the query optimizer dynamically computes intelligent defaults for parallelism based on the number of processors in the nodes of the cluster. An evaluation of the costs of alternative access paths, table scans versus indexed access, for example, takes into account the degree of parallelism (DOP) available for the operation. This results in Oracle selecting the execution plans that are optimized for your RAC configuration.
RAC takes full advantage of parallel execution by distributing parallel processing across all available instances. The number of processes that can participate in parallel operations depends on the DOP assigned to each table or index.
See Also:Oracle Database Performance Tuning Guide for more information about the query optimizer
You can control the instances that allocate parallel execution server processes with instance groups. To do this, assign each active instance to at least one or more instance groups. Then dynamically control which instances spawn parallel processes by activating a particular group of instances.
Note:An instance can belong to one or more groups. You can enter several instance group names with the