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Oracle RAC Cluster Tips by Burleson Consulting

This is an excerpt from the bestselling book Oracle Grid & Real Application Clusters.  To get immediate access to the code depot of working RAC scripts, buy it directly from the publisher and save more than 30%.

While not shown in the diagram, every component requires a connection to the others. This connection is usually via a network interface card (NIC) or host bus adapter (HBA) interface. These NIC or HBA interfaces should be the fastest possible, especially in the case of the cluster interconnect and disk connect. Failed NIC interfaces result in the loss of that component, unless a second NIC card is immediately failed over to. A failure of the HBA results in loss of connection to the disk array. At a minimum, a spare NIC and HBA for each and every component must be available. Wherever possible, use interchangeable NIC and HBA interfaces.

Provide Redundancy at Each Level

It is easy to see that redundancy at the hardware level is vital. At each level of the hardware layout an alternate access path must be available. Duplicating all equipment and configuring the automatic failover capabilities of the hardware reduce the chances of failure to virtually nil. It is also critical to have spares on hand for non-redundant equipment such as NIC and HBA cards and interface cables.

By providing the required levels of redundancy, the system becomes highly available. Once there is an HA configuration, it is up to the manager to plan any software or application upgrades to further reduce application downtime. In Oracle Database 10g using grid control, rolling upgrades are supported, further increasing reliability. At the SAN level, appropriate duplication software such as Veritas must be used to ensure the SAN arrays are kept synchronous. Oracle Database 10g allows for use of the Oracle Automatic Storage Management or ASM. ASM allows for automated striping, backup and database flashback capability.

Designing for High Performance

Designing for high performance means that every tier of the design must eliminate contention for resources. If there is no contention, each process gets the resources it needs to perform optimally.  Resources fall into multiple categories: physical, as in disk and network; and internal, such as CPU speed and memory capacity. Designing for performance means utilizing these resources properly and not relying on memory or disk resources to make up for poor application design.

As with normal databases, the application design will drive performance. The finest equipment will not make up for a poor application design. In the days of Oracle Parallel Server (OPS), Oracle recommended partitioning the application data and the servers to make OPS perform. Now, Oracle salesmen insist that any application can be run with RAC, with no need for changes.

To add capacity, the solution is to just add a server and bingo, more capacity is provided and more users, no matter what they do with the application, can connect. This all sounds wonderful until the manual, Oracle9i Real Application Clusters Deployment and Performance, Release 1 (9.0.1)", Part No. A96598-01, Chapter 3, Scaling Applications for Real Application Clusters, and Chapter 4, Scaling Applications for Real Application Clusters, is consulted. There, Oracle recommends partitioning both the application data and the users to optimize performance. This unfortunate fact is omitted from the 9.2 and 10g versions of the manual which seems to indicate the automated tuning features of 9.2 and 10g relieve the DBA of this arduous task.

Of course, the difference is that now partitioning is based on reducing intra-node block pinging between instances over the cluster interconnects, instead of reducing disk pinging. At most, a factor of 40 improvements can be expected for the same application running on a RAC server versus an OPS-based server. Once the various system latencies are added, the speed difference between memory operations and disk operations falls to approximately a factor of 40 between a disk ping and an intra-node memory ping. The speed is dependent upon the speed of the interconnect. Still, a factor of 4000% (40) is nothing to sneeze at.

Designing applications for better performance on RAC involves:

* Assigning transactions with similar data access characteristics to specific nodes.

* Creating data objects with parameters that enable more efficient access when globally shared.

* Automating free space allocation and de-allocation through the use of locally managed tablespaces.

* Automating block management through local freelist management.

* Using sequences properly by using sequence ranging triggers for each instance.

* Optimizing all SQL in the application.

* Understanding the workload on the system and planning the application to properly utilize resources.

These factors should be considered for proper application design one-by-one in order to see how they can be utilized to make RAC applications perform optimally.


This is an excerpt from the bestselling book Oracle Grid & Real Application Clusters, Rampant TechPress, by Mike Ault and Madhu Tumma.

You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts.


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Note: This Oracle documentation was created as a support and Oracle training reference for use by our DBA performance tuning consulting professionals.  Feel free to ask questions on our Oracle forum.

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