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Thread: ADDM for RAC 11G

  1. #1
    Expert Oracle Administrator
    Join Date
    Oct 2011
    New Delhi, India

    ADDM for RAC 11G

    One of the challenges with RAC is that it has it's own set of unique performance issues that need to be dealt with. In Oracle 10g and earlier you would need to use a number of GV$ views to analyze cluster related issues. Oracle 11g ADDM has a new layer of RAC specific analysis that has been added to it specifically designed to make ADDM RAC-aware.

    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, 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 new RAC specific ADDM processes are run after each AWR snapshot by default. ADDM can now provide reporting on the following conditions:

    - Excessive use of global resources such as IO and global locks

    - High-load SQL and resulting hot blocks

    - Global cache interconnect traffic

    - Network latency issues

    - Skewing in instance response times

    You enable RAC aware ADDM by calling the set_default_task_parameter attribute of the Oracle-supplied dbms_advisor PL/SQL package. Through this call you can set the value of the instances parameters, which will indicate which instances should receive Database ADDM analysis. The following table provides a look at the different settings you can use for the instances parameter.

    Instances Setting ADDM Analysis Mode Enabled

    UNUSED - Disables Database ADDM for all instances (default value)

    Comma-separated list of instances (numeric) Database ADDM will be done only for the instances listed
    ALL Enables ADDM for all instances

    Here are some examples of setting this parameter:

    Disable Database ADDM for all instances:
    Exec dbms_advisor.set_default_task_parameter('ADDM','IN STANCES','UNUSED');

    Configure Database ADDM for instances 1 and 3 only:
    Exec dbms_advisor.set_default_task_parameter('ADDM','IN STANCES','1,3');
    Configure Database ADDM for all instances

    Exec dbms_advisor.set_default_task_parameter('ADDM','IN STANCES','ALL');
    The results of the ADDM RAC analysis can be found in a OEM. For example, there is the Cluster database home page that displays information specific to cluster performance. A manual RAC report is also available with the dbms_addm package.

    To call the task may look like the following:

    exec dbms_addm.analyze_db(‘ADDM’, 10, 15);

    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(‘ADDM’) from dual;

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