RAC is a feature of Oracle Database beginning with Oracle 9i. OPS is a feature of Oracle 7 and Oracle 8 databases. GRID is a term that is over used in the industry. Oracle provides an enterprise grid architecture. RAC is an infrastructure used by many when implementing an enterprise grid architecture. I am sure if you do a bit of work you will find many white papers etc that give you more information
your answers are most valuable for me. especially i was considering that OPS is being rename to RAC in oracle 9i. so my understand about RAC and Grid is:
RAC is used for availbility purposes to avoid SPOF. RAC also acts a load balancing. But RAC is just a cluster its not many computer acting as one big computer. For example if we do parallel query in oracle RAC will only perform computing on the node on which query executed. RAC uses Net8 for load balancing.
acts as one big computer (MPP). if i run parallel query on one maching some part of the query will be executed on each maching provided these machine have sufficent resources.
Real Application Clusters provides the framework for parallel execution. Parallel execution performs efficiently in Real Application Clusters because it can distribute portions of a large SQL statement across multiple instances. The transaction is completed more quickly because it executes on multiple CPUs.
In Real Application Clusters, Oracle determines at runtime whether it will run parallel execution server processes on only one instance, or whether it will run processes on multiple instances. In general, Oracle tries to use only one instance when sufficient resources are available. This reduces cross-instance message traffic
Here Rac can do parallel processing acting as one big computer. I wonder then why they introduce grid.
RAC is a product that lets you use many machines for one purpose.
Enterprise Grid computing is an architectural approach where to achieve a shared, dynamic, flexible infrastructure for many applications or workloads on pools of machines at each layer (midtier, database, storage), w/ RAC as a tool at the database layer to allow this capacity pooling. See Gartner's Real Time Infrastructure definition for what the Enterprise Grid computing is trying to achieve.
Before knowing what is RAC you must know what a cluster is A cluster is a collection of servers (called nodes) operating as one unit. A cluster is useful for high performance and high availability. If your nodes cannot handle the tasks, add more nodes, which adds more resources to get the job done. If a node fails, the work can still continue on the other nodes. when it is used with RAC Real Application Cluster provides application support from any server (node) if any server is down or crashed your application is still working and ready to used from others node.
Grid computing enables the virtualization of distributed computing and data resources such as processing, network bandwidth.