Site icon Radu Pârvu

Understanding RAC One Node: Benefits and Drawbacks

Radu

“If it is not right do not do it; if it is not true do not say it.”
Marcus Aurelius

RAC OneNode (Real Application Clusters OneNode) is a feature of Oracle RAC (Real Application Clusters) that allows you to run a single instance of an Oracle database on one node of a clustered environment, with the option to easily relocate to another node if needed. It combines some of the high availability benefits of Oracle RAC with simpler management compared to a full RAC setup. This feature is a classic in the on-prem scenario but not seen too often in Cloud or even multi-Cloud implementation. Recently, I was asked to look into the feasibility of using it for ODAA. Here’s a breakdown of the benefits and cons of using RAC OneNode:

Benefits of RAC OneNode:
  1. Improved High Availability:
    RAC OneNode provides failover capabilities. If the primary node fails, the database instance can be relocated to another node in the cluster, minimizing downtime.
  2. Simplified Management Compared to Full RAC:
    Unlike a full RAC configuration, which requires managing multiple database instances across multiple nodes, RAC OneNode simplifies operations by running just one instance, but still allows relocation (switchover or failover).
  3. Scalability:
    You can easily scale up by converting the RAC OneNode to a full RAC configuration if the database workload increases, without needing significant changes to the infrastructure.
  4. Lower Cost Compared to Full RAC:
    RAC OneNode is generally more cost-effective than running a full RAC because it requires fewer licenses and resources since you’re only using one active node at a time.
  5. Workload Management:
    RAC OneNode supports Oracle Clusterware’s workload management features, such as server pools and policies, to help distribute load and manage resources in the cluster efficiently.
  6. Online Relocation:
    With RAC OneNode, the database instance can be relocated to another node without downtime using Oracle’s “online instance relocation” feature, which is beneficial for load balancing or performing maintenance on the current node.
  7. Database Consolidation:
    RAC OneNode allows the consolidation of multiple databases on a single node, enabling more efficient resource utilization across nodes in a cluster.
Cons of RAC OneNode:
  1. Not standard feature of ODAA but still supported as a manual setup according to Oracle
  2. Limited Node Usage:
    Unlike full RAC, where multiple nodes can handle the same database workload in parallel, RAC OneNode only uses one node at a time. This limits the performance benefits of distributing workloads across multiple nodes.
  3. Less Availability than Full RAC:
    Although RAC OneNode offers high availability through instance relocation, it doesn’t provide the same level of availability as full RAC, where multiple nodes can failover instantly.
  4. Relocation Complexities:
    While instance relocation is supported as you can use the srvctl, strange “feature” is that the instance name changes depending are you doing a failover or switchover. Ref: Instance Name changes during RAC One Node Failover/Switchover (Doc ID 1540629.1). This may not meet the high availability requirements of certain critical systems.
  5. Potential for Single Point of Failure:
    If proper planning is not in place, RAC OneNode could still face downtime during a node failure before relocating to another node, which isn’t as robust as full RAC’s instant failover.
  6. Complex Licensing:
    Oracle licensing can be complex, and RAC OneNode might still incur higher costs compared to non-RAC solutions. Also, if you decide to upgrade to a full RAC configuration, additional licensing costs will apply.
  7. Not Ideal for Heavy Workloads:
    If your database is under heavy load and needs to use multiple nodes simultaneously, RAC OneNode may not be sufficient, and a full RAC setup would be better suited for such workloads.
  8. Requires Oracle Clusterware:
    RAC OneNode still depends on Oracle Clusterware for management and failover capabilities, so it doesn’t eliminate the need for managing cluster infrastructure.

In summary, RAC One Node is ideal for users who need high availability and scalability with simplified management compared to full RAC, but its limitations in node usage and potential downtime during relocation make it less ideal for very high availability or performance-critical environments.

Statement re the feature being supported in Cloud

I was told by Oracle that the RAC One Node feature is not supported nor certified on any Cloud database offerings. Nevertheless, the only Oracle white paper on One Node advertises it as it is actually a good solution for Cloud deployments! So the Clients might find themselves into a no man’s zone when it comes to supporting this feature on Cloud. Hopefully, Oracle will decide to clarify this soon.

Exit mobile version