Introduction and considerations

Oracle Parallel Server (OPS) and Real Application Cluster (RAC) offer superior scalability through the distribution of workload across nodes, and high availability through multiple nodes accessing the database. If one node fails, the database is still accessible through the surviving nodes.

Approaches discussed above use the IP-failover mechanism and use clustering software to manage the resource group. The failover time is usually in the range of one to five minutes. Some parallel database servers, such as Oracle Parallel Server (OPS) and Real Application Cluster (RAC) not only provide greater scalability, but also facilitate faster failover, since the instance is pre-existent in the backup system. Although OPS is not registered with or managed by the cluster resource group manager, it still relies on a clustering software layer to query cluster information. Therefore, platform-specific clustering software such as HACMP, MC/ServiceGuard, or Sun Cluster, is required for OPS/RAC to function in a clustered environment. The OPS/RAC system consists of an operating system-dependent layer (platform-specific cluster software), Oracle 8i/9i Enterprise Edition, Oracle Parallel Server Option, and Oracle Parallel Server Management. Inside OPS, there are Integrated Distributed Lock Management (DLM), Parallel Cache Management (PCM), and Oracle Parallel Query.

You can configure OPS/RAC to use the shared-disk architecture of the cluster software. In this configuration, a single database is shared among multiple instances of OPS/RAC that access the database concurrently. The Oracle Distributed Lock Manager controls conflicting access to the same data. If a process or a node crashes, the DLM is reconfigured to recover from the failure. If a node failure occurs in an OPS/RAC environment, you can configure Oracle clients to reconnect to the surviving server without the use of the IP failover, as detailed in 12.1, WebSphere with IBM HACMP through 12.6, Programming clients for transparent failover. The multiple Oracle instances cooperate to provide access to the same shared database. The Oracle clients can use any of the instances to access the database. Thus, if one or more instances have failed, clients can connect to a surviving instance and continue to access the database.

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