Monday, September 3, 2012


Hello friend, this is my first article for RAC and in this article I am just going to discuss few basic evolutionary information about Oracle RAC. 

Very soon I'll write few other articles about RAC...

1. oracle cluster database was introduces with oracle 6 for DIGITAL VAX cluster product.

2. Oracle was the first product that support clustering at database level.

3. In the same version oracle create LOCK MANAGER for VAX/VMS  cluster but that was not very scalable and DB requires locking at block level.

4. Oracle 6.2 gave birth to OPS (OPS was used till 8i from 9i onward oracle start using RAC).

5. Oracle 6.2 was the first database that run the parallel server.

6. That time many UNIX vendor started cluster but they all were using Oracle DLM.

7. Oracle 7 OPS used vender-supplied clusterware.

8. OPS was avalaible for all vendor but main drawback was complexity with configuration.

9. Oracle 8 introduce GENERIC LOCK MANAGER

10. Then oracle intergrate LOCK MANAGER with oracle code with additional layer called OSD (OPERATING SYSTEM DEPENDENT).

WHAT IS OSD (Oracle Disk Manager)

Oracle provides cluster software (or OSD – operating system dependent layer) to the windows cluster for the use of RAC. This is different from the Microsoft Cluster Service software that Microsoft provides for windows clustering. The Microsoft MSC deals with the failover type of clustering.

Vendors provide the OSD clusterware for UNIX operating systems, and Oracle provides the OSD clusterware for Windows NT and Windows 2000 operating systems. The OSD has the following subcomponents:

a. The Cluster Manager
b. The Node Monitor
c. The Interconnect

The Cluster Manager

The cluster manager (CM) oversees internode messaging that travels over the interconnect to coordinate internode operations. The cluster manager also provides a global view of the cluster and the nodes and instances that are members of it. The cluster manager also controls cluster membership.

The Node Monitor

The cluster manager includes a subset of functionality known as a node monitor. The node monitor polls the status of each resource in the cluster including the nodes, the interconnect hardware and software, and the shared disks. In the Oracle-supplied Cluster Manager for Windows, the node monitor also polls the Oracle instances.

The cluster manager informs clients and the Oracle server when the status of cluster resources change. This is because Real Application Clusters manages cluster membership by reconfiguring the cluster database when a joining instance registers with the cluster manager or when an existing instance disconnects from it.

The node monitor also serves the cluster manager by:

- Providing node management interface modules
- Discovering and tracking the membership states of the nodes by providing a common view of node membership across the cluster
- Detecting and diagnosing changes in the states of active nodes and communicating information about those change events

The Interconnect

The interprocess communication (IPC) software, or interconnect, is another key OSD component. The IPC controls messaging among the nodes. Real Application Clusters also uses the IPC to transfer data blocks between instances.


11. Very soon Oracle's LOCK MANAGER intregated with oracle Kernel and became known as IDLM(Intregated Distributed Lock Manager).

12. Oracle 9i RAC start using IDLM but still It was using external clusterware.

13. With 9i oracle introduce its own clusterware but only for WINDOWS & LINUX.

14. From 10g onward its provide its own clusterware for all other OS.

15. In 11g its became more powerful with SERVERPOOL and with additional API to manage third party applications.

16. So finally with 9i oracle launch RAC but few constraints was there that was hampering the adoption of RAC and those constraints were-

a. The unavailability of general-purpose clusterware
b. The cluster-wide filesystem

17. With 9i, oracle solve both the issues that was hampering the adoption of RAC with the help of:

b. Oracle also developed cluster filesystem called as ORACLE CLUSTER FILESYSTEM (OCFS).

18. Now, stll few restriction was there with OCFS - OCFS has inherent limitations and was not very scalable large no. of cluster nodes and also OCFS was only ported for LINUX & WINDOWS.

19. So to solve the above limitation Oracle introduced another product in Oracle 9i Release 2 called ORACLE DISK MANAGER (ODM) for Solaris OS. 

Now the question is how ODM is good???

ODM was capable of handling file management operations and also ODM replaced FILE DISCRIPTER with FILE IDENTIFIER and start caching this FILE DISCRIPTER in SGA to reduce the kernel overheads for file lookups and file I/O operations.

20. With the success and wisdom gained by ODM, oracle was ready to launch fully functional and cluster-aware file system called ASM with oracle 10g.


1 comment:

  1. Thanks Ashish for sharing such detail information.