RAC

Real Application Clusters (RAC) allows multiple computers to Run RDBMS software, simultaneously, while accessing a single database and providing a clustered database.

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 of the computer and have access to a single coordinated set of data. RAC addresses areas such as fault tolerance, load balancing, and scalability.