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Oracle 11g Cluster Performance

Oracle 11g New Features Tips by Burleson Consulting
June 29, 2008

Oracle 11g SQL New Features Tips

Oracle RAC carries the promise of better performance through horizontal scalability.  With proper load balancing, dividing the work among multiple nodes allows for greater throughput overall.  For instance, if a single instance is highly I/O bound, the CPU may be wasted due to the physical I/O bottleneck.  With RAC and services, the load can be distributed to multiple servers, allowing more resources to be used across the board.

In order to monitor and tune the system, Oracle introduced the AWR and Automatic Database Diagnostic Monitor ADDM in Oracle 10g.  The AWR is not only responsible for storing database snapshot statistics for automatic tuning, but also for producing reports that are useable by a Remote DBA to further tune their system.  ADDM creates human readable suggestions on ways to optimize the performance by eliminating bottlenecks based on information from the AWR.  In Oracle 11g, ADDM reports have been extended to also provide diagnostic information about RAC clusters.


The Automatic Database Diagnostic Monitor (ADDM) was introduced in Oracle 10g.  Using information from the AWR, ADDM would provide “plain English” solutions to the Remote DBA in the form of findings.  The report would show the impact of issues on a database instance and offer solutions to fix the problem.

In Oracle 11g, ADDM has been extended to include RAC, and provides information on the entire cluster including latency issues on the cluster interconnect, global cache hot blocks (blocks with concurrency issues across multiple nodes), and general object usage information across multiple nodes.

The key to using ADDM for RAC is running the tool in database mode.  Remember that a RAC cluster is a single database with multiple instances; normally ADDM is run against an instance.  In database mode, a single instance system will run the same; however, a RAC cluster will report on multiple nodes.

Creating an ADDM Task

If the object is to run in database mode, the following syntax can be used:

exec dbms_addm.analyze_db( -
task_name => ‘name for your task’, -
begin_snapshot => begin_snapshot_num, -
end_snapshot => end_snapshot_num, -
db_id => db_id_optional –

For example, a call to the report may look like the following:

exec dbms_addm.analyze_db(‘My ADDM Task’, 100, 102); 

Note that an ADDM report can also be run for RAC across a subset of instances in the cluster using DBMS_ADDM.ANALYZE_PARTIAL.  For instance:

exec dbms_addm.analyze_partial(‘My Partial ADDM Task’, ‘1,2’, 100, 102); 

The second parameter (with value ‘1,2’) represents the instance numbers that should be analyzed ADDM report.

Gathering the Report

The report can be gathered via a function called DBMS_ADDM.GET_REPORT.  The task name that was assigned the ADDM run will be needed.

set long 9999999
set pages 0
select dbms_addm.get_report(‘My ADDM Task’) from dual;

The reports in Database Control can also be viewed on the Cluster Database home page.  The report is found under the “Diagnostic Summary” area by clicking the link next to “ADDM Findings”.  Doing so will allow a graphical version of the ADDM report to be viewed. 

High Availability

The high availability enhancements to Oracle 11g primarily focus upon upgrading, which is considered planned downtime.  However, there are times when planning downtime is difficult.  Oracle 11g alleviates this issue by allowing cluster nodes to be patched to the latest release one node at a time, allowing the entire cluster to remain online longer.

Please note that it is always advisable to perform a backup before attempting any upgrade, rolling or otherwise.  In addition, rolling upgrades are not possible if a shared home is used for the Clusterware, ASM, or Oracle Database.

This is an excerpt from the new book Oracle 11g New Features: Expert Guide to the Important New Features by John Garmany, Steve Karam, Lutz Hartmann, V. J. Jain, Brian Carr.

You can buy it direct from the publisher for 30% off.

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