Node and Instance in Oracle RAC

Balajidba

Hi ,

Can someone explain the below concept of instance and node in Oracle RAC with example?

An instance can access one and only one database. With Oracle RAC, there are multiple instances for one database. Each instance runs on a separate database server, called a node in the cluster

Regards,

Balaji

Markus Flechtner

node = host, server

instance = database instance running on a node

in a RAC database you've got multiple database instances (which are running on different nodes) which use the same database (=set of datafiles on shared storage)

There's a nice Oracle Documentation on that:

https://www.oracle.com/webfolder/technetwork/tutorials/architecture-diagrams/19/rac/main.html

HTH

Markus

Markus Flechtner

node = host, server

instance = database instance running on a node

in a RAC database you've got multiple database instances (which are running on different nodes) which use the same database (=set of datafiles on shared storage)

There's a nice Oracle Documentation on that:

https://www.oracle.com/webfolder/technetwork/tutorials/architecture-diagrams/19/rac/main.html

HTH

Markus

Balajidba

Thanks Markus for your explanations along with link.

Balajidba

Hi Markus,

The database instance can be relocated to another node in the cluster while maintaining application continuity. 

Could you please explain this sentence? To me only users will be relocated to another surviving node when the current node is down.

Regards,

Balaji

Balajidba

Hi Markus,

https://www.oracle.com/webfolder/technetwork/tutorials/architecture-diagrams/19/rac/main.html

The above link is for  Oracle Real Applications Cluster 19c Technical Architecture. Similarily can you send the link for Oracle11g or 12c.

Regards,

Balaji

Markus Flechtner

Hi,

taking the general architecture, there are no major differences between RAC in 11g, 12c, 18c and 19c.

If you want to know more about the differences between the versions you mentioned, please check the Oracle documentation:

https://docs.oracle.com/en/database/oracle/oracle-database/index.html

HTH

Markus

Markus Flechtner

Basically, not "users" but "user sessions" are moved to the other node.

Application continuity takes care that no statements are lost.

For more information, please see https://www.oracle.com/database/technologies/high-availability/app-continuity.html

HTH

Markus

Balajidba

Hi Markus,

If you want to know more about the differences between the versions you mentioned, please check the Oracle documentation:https://docs.oracle.com/en/database/oracle/oracle-database/index.html

You have shared Oracle database link. Kindly send Oracle RAC.

Markus Flechtner

There's a link "Clustering" ...

Balajidba

May I know where can I find that link

Regards,

Balaji

BPeaslandDBA

The database instance can be relocated to another node in the cluster while maintaining application continuity. Could you please explain this sentence? To me only users will be relocated to another surviving node when the current node is down.

In admin-managed RAC databases, which most of today's Oracle DBAs use, an instance cannot be relocated to another node in the cluster. The sessions can failover to another instance on another node, as already discussed, but the instance on the downed node is not moved.

If you use policy-managed RAC databases, then the instance can move to another node in the same server pool.

Cheers,

Brian

Balajidba

Thanks Brian for your explanation on RAC.

When user session is moved to another instance, it moves to node 2 or node 3 or based on workload it failovers.

Could you please explain this failover concept.

Regards,

Balaji

Sunny kichloo

Do check this

https://docs.oracle.com/en/database/oracle/oracle-database/19/rilin/load-balancing-of-connections-to-oracle-rac-databases.html#GUID-06B4373D-1217-44E4-BD86-DE353DA657F6

Balajidba

Hi Sunny,

Thanks for the link.

Regards,

Balaji

Sunny kichloo

Welcome

eronitascott

Helpful to me. thank you for sharing.

Oracle RAC is a cluster database with a shared cache architecture that overcomes the limitations of traditional shared-nothing and shared-disk approaches to provide highly scalable and available database solutions for all business applications.

Balajidba

Thank you