Real Application Cluster
Oracle RAC allows multiple computers to run the Oracle RDBMS software simultaneously while accessing a single database. This is clustering in oracle.
In an Oracle database, a single instance accesses a single database. The "database" consists of a collection of data files, control files, and redo logs located on disk.
In an Oracle RAC environment, two or more computers (each with an instance) concurrently access a single database. This allows an application or user to connect to either computer and have access to a single coordinated set of data.
Computers/instances in an RAC access the same database, the overall system must guarantee the coordination of data changes on different computers. Oracle RAC refers to this functionality as Cache Fusion. Cache Fusion involves the ability of Oracle RAC to "fuse" the in-memory data cached physically separately on each computer into a single, global cache.
In RAC the node performing the write-transaction must take ownership of the relevant area of the database: typically this involves a request across the cluster interconnection (local IP network) to transfer the data-block ownership from another node to the one wishing to do the write. This takes a relatively long time (from few milliseconds to tens of milliseconds) compared to single database-node using in-memory operations.
To Install RAC Download
Download VMware Server
Download Enterprise Linux
Download Oracle Database(10201_database_linux32.zip) & Oracle clusterware (10201_clusterware_linux32.zip)