Oracle: Real Application Clusters (RAC)


We are all aware of the fact that demand for Oracle is growing day by day in terms of knowledge, resources required in any firm and so on. Have you thought why Oracle? Why not SQL, MONGODB? In this article, you will find out after reading that Oracle has provided many wonderful features like Real Application Clusters (RAC), and that's why the demand is growing day by day.

In India, the big example and familiar example that I can give you is IRCTC. This is a superb example to explain. Have you ever booked tickets on a website (say, railway tickets) and have you seen how they pooled the connections? At any given point of time, lots of people are connected and tring to book the tickets during peak seasons. Have you ever noticed the page dropped or connectio was lost while booking a ticket? The answer is no, whether you are booking a normal ticket or a tatkal ticket; it seems to be super-fast. Here, IRCTC follows RAC architecture.


Today, for a successful firm or any business you need to be flexible, scalable,have high availability and so on, in order to be successful in terms of IT. Consider IRCTC, if that website wasn't available when you needed it the most. The Oracle Real time clustering, also called  real application clusters, has been the perfect solution to these kind of systems. The latest release of Oracle 12c had added some new features in Oracle RAC architecture. Let’s have a look at Oracle RAC Architecture. 


Image source - Google

Here, in this architecture you can clearly see the Application/Web Servers that are actually connecting the nodes. Here, the nodes are nothing but the clusters. Cluster Server is nothing but different Servers that share the same interface. 

The database here are HR, sales and call center follow cluster setup. The same multiple database instance is shared on the different Servers and the same database file is shared too. They are connected by a common RAC database.

Oracle Application Clusters (Detail)

Here an Oracle RAC consists of,
  • Oracle Cluster ware.
  • ASM(Automatic Storage Management).
  • Oracle cloud file system.

Let’s see one by one,

Oracle Cluster ware

Oracle cluster ware is the one that brings multiple nodes or clusters and treats it as a single entity. Oracle cluster ware is crucial for Oracle RAC architecture.

ASM (Automatic Storage management)

Since Oracle RAC follows a shared disk mechanism. With the help of ASM, Oracle RAC is possible and it’s a volume manager.

Oracle Cloud File System

It checks to store their up times, volumes, space and SAN. 

Oracle RAC Overview

Image source - Google and online multiple sources

In the diagram shown above, the client communicates with the shared Server environment. Now imagine the number of the clients are connected with a shared environment. With Oracle RAC, load balancing is possible, as with the failure of one node, you can redirect the traffic to another nodes as well.

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That’s all from Oracle RAC structure. If you have any doubts regarding this topic, feel free to ask.