Database Resource Manager (DRM).
Database Resource Manager (DRM).
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The Database Resource Manager (DRM) is a DBA tool available in Oracle 10g. It helps to allocate resources to various resource consumer groups based on the criticality of a particular task. It also gives the Oracle database server more control over resource management decisions.
The Database Resource Manager (DRM) was introduced in 8i and is improving with every subsequent releases of the Oracle. DRM is supported only for utilities that use technologies such as processor sets or domain to isolate each database instance into its own virtual partition. The main function of DRM is to manage resources of a system. DRM also handles the resource plans of a database. A resource plan comprises of the rules and the plan directives. These rules and the directives can be applied for consumer groups, resource plans, etc. However, only one plan can be active per database instance. By default, DRM remains disabled until any active plan is selected for a system. DRM should be enabled on each instance in any RAC environment, as it acts at the instance level. Oracle DRM is a tool that is considered for running a high loaded system with a variety of applications.
Following window describes how to create a resource plan.
A resource plan consists of consumer groups, subplans, etc. They let to finally control the resource allocation. Oracle EM can be used to create and manage all the elements of a database. The EM Database Control can be used to start the DRM. Before, creating a new resource plan a few consumer groups should be created. The switch_time_in_call and switch_time directives enhance the switching capability of the consumer groups. The DBMS_RESOURCE_MANAGER_PRIVS package is used to grant permission to switch consumer groups. The resource management and the system management are critical to maintain application and database performance, scalability, and availability. Therefore, DRM enables DBA's to allocate CPU resources among database users and applications as well as limit the degree of parallelism of any operation.
The enhancements in 9i can detect long running queries and operations and limits their resource consumption thereby preventing the system wide performance degradation. In rare cases, DRM prevents the operations from being started up, if they are expected to run for an unexpectedly long time, thereby consuming excessive system resources.
DRM allocates resources among users or applications based on a specific resource plan. A resource plan consists of directives that decide how resources should be distributed among various applications, sessions, and active users. Users or applications are grouped together into various resource consumer groups based on resource requirements and business priorities. A resource plan can be created to distribute system CPU resources among high, medium, and low priority consumer groups.
The nested plans are also known as subplans. Subplans are used to re-partition resources within an application. Available resources can also be allocated within a resource plan at multiple levels.
Following figure depicts how the resources are allocated within a resource plan at multiple levels:
An example of implementation of DRM in an online transaction processing is the ATM application. In the ATM application, online processing and batch processing go hand in hand. Therefore, resources are needed to be partitioned, such as for ATM users keep the 90% of the available resources and for batch processing keep the 10% of the available resources.
DRM is a fully integrated component of the database security system. The operations such as creating, updating, or deleting resource plans and resource consumer groups can be performed by using either a PL/SQL interface or a Oracle 9i EM console.
Earlier all database users and applications had been provided equal access to database resources, however, the concept of providing equal access to database resources failed to qualify the basic needs of a business. Some activities in an enterprise are more crucial and critical than others. Therefore, the system resources should be in a hierarchical order. The 8i DBAs were able to implement resource allocation policies to guarantee measured database services to enterprise, applications and users. The enhancement of DRM in 9i made it more automated, powerful, and proactive. It also made the existing services and predictable service levels easy to deliver with minimal human intervention and facilitates almost unlimited system scalability without compromising performance.
The elements of DRM are mentioned below:
- Resource Consumer Group
- Resource Plan
- Resource allocation method
- Resource Plan Directive
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