Instance Caging to Manage CPU Usage in Oracle Database 11g Release 2
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 has been available in the Oracle database since Oracle 8i and has gone through significant improvements in every major release. You can read more about it here:
- Resource Manager in Oracle 8i
- Resource Manager Enhancements in Oracle 9i
- Resource Manager Enhancements in Oracle 10g
- Resource Manager Enhancements in Oracle 11g
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; PLAN ------------------------------ DEFAULT_PLAN INTERNAL_QUIESCE INTERNAL_PLAN APPQOS_PLAN DEFAULT_MAINTENANCE_PLAN ETL_CRITICAL_PLAN MIXED_WORKLOAD_PLAN ORA$AUTOTASK_SUB_PLAN ORA$AUTOTASK_HIGH_SUB_PLAN DSS_PLAN 10 rows selected. SQL>
If you have no specific resource management needs within the instance, the simplest solution is to use the default plan.
ALTER SYSTEM SET RESOURCE_MANAGER_PLAN = 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_COUNTset 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_COUNTvalues 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.
The diagram below gives and example of the two provisioning methods on an 8 CPU/Core server.
The CPU_COUNT can vary for each instance, to indicate their relative performance requirements.
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.
SQL>
ALTER SESSION SET nls_date_format='DD-MON-YYYY HH24:MI:SS';
SET LINESIZE 100
SELECT begin_time,
consumer_group_name,
cpu_consumed_time,
cpu_wait_time
FROM v$rsrcmgrmetric_history
ORDER BY begin_time;
BEGIN_TIME CONSUMER_GROUP_NAME CPU_CONSUMED_TIME CPU_WAIT_TIME
-------------------- ------------------------------ ----------------- -------------
.
.
.
03-NOV-2012 14:31:20 ORA$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.
SQL>For more information see:
- Managing Multiple Database Instances on a Single Server
- Resource Manager in Oracle 8i
- Resource Manager Enhancements in Oracle 9i
- Resource Manager Enhancements in Oracle 10g
- Resource Manager Enhancements in Oracle 11g
Hope this helps. Regards Tim...
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