A Cluster requires an additional network to the Local Area Network (LAN) that a database server is attached to for application connections. A cluster require a second server is attached to for application connections. A cluster requires a second private network commonly known as the interconnect. Oracle recommends that you use 2 network interfaces for this network for high availability purposes. A network interface bonding external to Oracle should be used to provide fail over and load balancing. The interconnect is used by cluster for inter-node messaging. The interconnect is also used by RAC to implement the cache fusion technology.

Virtual Internet Protocol Address (VIP)

Oracle RAC 10g requires a virtual IP address for each server in the cluster. The virtual IP address is an unused IP address on the same subnet as LAN. This address is used by application to connect to the RAC database. If a node fails, the virtual IP is failed over to another node in the cluster to provide an immediate note down response to connection requests.

Benefits of Real Applications Clusters

Scalability

Scalability is the ability to add additional nodes to Real Application Clusters and achieve markedly improved performance. Real Application Clusters can take advantage of additional equipment and harness the processing power of multiple systems. All servers in the cluster must run the same operating system and same version of oracle but they do not have to be exactly the same capacity.

High Availability

The term high availability refers to systems with redundant components that provide consistent, uninterrupted service, even in the event of hardware or software failures. In most high availability configurations, nodes are isolated from each other so a failure at one node does not affect the entire system. In such a case, surviving nodes compensate for the loss of the failed node through recovery and the system continues to provide data access to users. This means data is consistently available, more so than it would be with a single node upon node failure. High availability also implies increased database availability.

Transparency

The concept of transparency is the functional equivalent of single instance Oracle and shared configurations that use Real Application Clusters. Applications that run on single instance Oracle execute with the same results using Real Application Clusters. An Oracle database can be configured to execute in three different modes:

• Single instance exclusive • Shared with a single instance • Shared with two or more instances

Buffer Cache Management

Within a single instance, Oracle stores resources, such as data block information, in a buffer cache that resides in memory. Storing this information locally reduces the disk Input/Output (I/O) necessary for database operations. Since each node in Real Application Clusters has its own memory that is not shared with other nodes, Real Application Clusters must coordinate the buffer caches of different nodes while minimizing additional disk I/O that could reduce performance. The Oracle Global Cache Service technology maintains the high-performance features of Oracle while coordinating multiple buffer caches.

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