Oracle RAC allows multiple computers to run the Oracle RDBMS software simultaneously while accessing a single database, thus providing a clustered database. In a non-RAC Oracle database, a single instance accesses a single database. Gartner analyzed the usage in early 2003 with Oracle Database 9i (9i) RAC. It was a very complex application at that time and required an skilled DBA to monitor it. But, in the last five years, Oracle made a significant improvement for RAC in terms of business value and lowered the skill level.
The notable points of Gartner after the survey is:
Oracle significantly improved RACs usage with Oracle Database 10g and Oracle Database 11g.
More than 15,000 companies are using RAC.
The key benefits of RAC are horizontal scalability on lower-cost hardware and sharing capacity across database management system (DBMS) instances in a grid.
Linux is an important platform to run Oracle DBMS. At least 30% of RAC installed bases are on Linux.
The specific benefits that Oracle customers mentioned in the survey are:
Shared infrastructure and storage: The Automated Store Manager is easier to use and enables customers to manage many databases in a single cluster of server nodes. Nodes can run any database instance. DBAs can optimize the capacity of each individual database by scheduling or manually initiating capacity increases or decreases.
Active/active processing: RAC enables full use of acquired capacity, rather than operating in active/passive mode.
Horizontal scale and lower-cost x86 servers: Many RAC customers buy into the grid concept by justifying using lower-cost x86 servers, rather than using more-expensive Unix SMP systems. Clients stated they found 80% or more scaling of new nodes added to the grid (10 to 18 nodes total).
Planned downtime: This referred to migrating instances between nodes to enable hardware and OS maintenance without affecting users.
Unplanned downtime: Failover time is typically less than one minute. However, depending on the type of application, some organizations measured failover time in tens of seconds.
DBA efficiencies of up to 50% savings over managing 9i RAC: DBAs can provision nodes faster, as well as manage storage and tune the environment with fewer resources.
Single integrated stack of software (RAC DBMS, ASM and Grid Control) with one-stop support: All the customers that Gartner spoke with reported outstanding support by Oracle for their RAC environments. While all these customers continued to use the OS supplier for OS support, those using Linux noted Oracles considerable knowledge on the OS side, which aided support calls.