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Real Application Clusters (RAC) is a parallel database environment that takes advantage of the processing power of multiple computers. The Oracle database is the physical data stored in tablespaces on disk, while the Oracle instance is a set of processes and shared memory that provide access to the physical database. Specifically, the instance involves server processes acting on behalf of clients to read data into shared memory and make modifications to it, and background processes to write changed data to disk.
In traditional environments, only one instance accesses a database at a specific time. SF Oracle RAC enables all nodes to concurrently run Oracle instances and execute transactions against the same database. This software coordinates access to the shared data for each node to provide consistency and integrity. Each node adds its processing power to the cluster as a whole and can increase overall throughput or performance.
At a conceptual level, SF Oracle RAC is a cluster that manages applications (instances), networking, and storage components using resources contained in service groups. SF Oracle RAC clusters have many of the same properties as Veritas Cluster Server (VCS) clusters:
SF Oracle RAC adds the following technologies, engineered specifically to improve performance, availability, and manageability of Oracle RAC environments, to a failover cluster environment:
SF Oracle RAC provides an environment that can tolerate failures with minimal downtime and interruption to users. If a node fails as clients access the same database on multiple nodes, clients attached to the failed node can reconnect to a surviving node and resume access. Recovery after failure in the SF Oracle RAC environment is far quicker than recovery for a failover database because another Oracle instance is already up and running. The recovery process involves applying outstanding redo log entries from the failed node.
SF Oracle RAC architecture
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