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Sunday, August 31, 2014

Instance Caging to Manage CPU Usage in 11g R2

Managing CPU usage can be an issue when trying to consolidate multiple databases on to a single server, because if one database starts to hog all the CPU on the server, all the other databases will be affected.

Instance caging is a new feature in the Enterprise Edition of Oracle Database 11g Release 2 (11.2) that simplifies the management of CPU usage in consolidation environments. By enabling Resource Manager and setting the CPU_COUNT parameter in each instance, you can limit the maximum amount of CPUs/Cores the instance can use.

Enabling Resource Manager:

Resource Manager is not enabled by default, so it must be enabled by specifying a resource plan before instance caging can take effect. Oracle provide a number of resource plans out of the box.

    SELECT plan FROM dba_rsrc_plans;


    10 rows selected.


If you have no specific resource management needs within the instance, the simplest solution is to use the default plan.


Remember, the maximum utilization of each consumer group within a resource plan is a proportion of the total CPU for the instance, specified by the
CPU_COUNT parameter. If a consumer group is limited to 50% of the total CPU and the CPU_COUNT is set to 2, then the consumer group is limited to 1 CPU.
Keep this in mind when using resource plans that control CPU utilization within the instance.

Setting CPU_COUNT:

With the Resource Manager active, you must set the CPU_COUNT for each instance running on the server. The CPU_COUNT parameter is dynamic, but it is not recommended to change it too often, or by too large an amount. The following command shows how to set the parameter.

    ALTER SYSTEM SET cpu_count = 2;

Setting the parameter is easy, but knowing what to set it too can take a little thought. There are two basic approaches:

Over-Provisioning: Each instance has its CPU_COUNT set to value less than the total number of CPUs on the server, but they add up to a value greater than the CPU count of the server. This prevents any one instance hogging all the server CPU, but if all instances are busy at the same time, the server can still get swamped.

Partitioning: The sum of CPU_COUNT values of all the instances on the server are less than or equal to the total number of CPUs on the server.
This way it is unlikely that any one instance will affect the performance of any other instance from a CPU perspective.

Monitoring Instance Caging:

The throttling effect of Resource Manager can be displayed using the CONSUMED_CPU_TIME and CPU_WAIT_TIME columns of the following views.


The CONSUMED_CPU_TIME is the number of milliseconds of CPU time consumed by the consumer group, while the CPU_WAIT_TIME is the time waiting for CPU due to Resource Manager throttling.

    SELECT name, consumed_cpu_time, cpu_wait_time
    FROM v$rsrc_consumer_group;

    NAME                             CONSUMED_CPU_TIME   CPU_WAIT_TIME
    -------------------------------- ----------------------------       -----------------------
    SYS_GROUP                                               45155            226
    OTHER_GROUPS                                          310                 4
    ORA$AUTOTASK_MEDIUM_GROUP     23805           864
    ORA$AUTOTASK_URGENT_GROUP       3777            17
    ORA$AUTOTASK_STATS_GROUP                  0             0
    ORA$AUTOTASK_SPACE_GROUP                  0             0
    ORA$AUTOTASK_SQL_GROUP                       0             0
    ORA$AUTOTASK_HEALTH_GROUP               0             0
    ORA$DIAGNOSTICS                                       375            13
    _ORACLE_BACKGROUND_GROUP_               0             0

    10 rows selected.


    ALTER SESSION SET nls_date_format='DD-MON-YYYY HH24:MI:SS';

    SELECT begin_time,
    FROM   v$rsrcmgrmetric_history
    ORDER BY begin_time;

  -------------------- -------------------------------------    --------------------------------- -----------------------
    03-NOV-2012 14:31:20 ORA$AUTOTASK_HEALTH_GROUP              0             0
    03-NOV-2012 14:31:20 ORA$DIAGNOSTICS                                          0             0
    03-NOV-2012 14:31:20 ORA$AUTOTASK_STATS_GROUP                   0            0
    03-NOV-2012 14:32:20 SYS_GROUP                                                     515            0
    03-NOV-2012 14:32:20 OTHER_GROUPS                                                0             0
    03-NOV-2012 14:32:20 ORA$AUTOTASK_MEDIUM_GROUP             0             0
    03-NOV-2012 14:32:20 ORA$AUTOTASK_URGENT_GROUP             0             0
    03-NOV-2012 14:32:20 _ORACLE_BACKGROUND_GROUP_             0             0
    03-NOV-2012 14:32:20 ORA$AUTOTASK_SPACE_GROUP                  0            0
    03-NOV-2012 14:32:20 ORA$AUTOTASK_SQL_GROUP                       0            0
    03-NOV-2012 14:32:20 ORA$AUTOTASK_HEALTH_GROUP               0            0
    03-NOV-2012 14:32:20 ORA$DIAGNOSTICS                                           0            0
    03-NOV-2012 14:32:20 ORA$AUTOTASK_STATS_GROUP                    0            0

    420 rows selected.


1 comment:

Sridevi K said...

Sridevi Koduru (Senior Oracle Apps Trainer
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