Introduction to Oracle RAC

 Introduction to Oracle RAC

Non-cluster Oracle database have a one-to-one relationship between the Oracle database and instance. Oracle RAC (Real Application Cluster) database have a one-to-many relationship between the database and instance.

A cluster comprises multiple interconnected computers or servers that appears as if they are one server to the users and applications.

Oracle RAC database differs architecturally from non-cluster database in that :

• Each instance has its own thread of redo groups.
• Each instance has its own Undo tablespace.

Oracle RAC used Oracle Clusterware software for the infrastructure to bind multiple servers so they operate as a single system.

Oracle Clusterware
Oracle Clusterware is a portable cluster management software that is integrated with Oracle RAC database and provides the infrastructure necessary to run Oracle RAC.
Oracle Clusterware also manages resources such as

• Virtual IP (VIP) adresses, 
• Databases, 
• Listeners, 
• Services and so on.

In addition, Oracle Clusterware enables both non-cluster Oracle database and Oracle RAC database to use the Oracle High Availability infrastructure. Oracle Clusterware and Oracle ASM enables you to create a clustered pool of storage to be used by any combination of non-cluster and Oracle RAC database.

Oracle clusterware is the only clusterware that you need for most platforms to operate Oracle RAC. If you use vendor clusterware, then you can use such clusterware in conjunction with Oracle clusterware if that vendor clusterware is certified for Oracle RAC.