How does Database Resource Manager perform database resource management?

Are you preparing for IT certification? With practice questions, study notes, interactive quizzes, tips and technical articles, uCertify PrepKits ensure that you get a solid grasp of core technical concepts to ace your certification exam in first attempt.

How does Database Resource Manager perform database resource management?

Rating:

The Database Resource Manager (DRM) is a tool, which handles the resource allocation issues in a more efficient way than can probably be done by the operating system itself. Such issues include equal distribution of resources by the operating system to every active process, inability of the operating system to prioritize the tasks, and inability of the operating system to manage database-specific resources. This tool has been provided with all versions after Oracle7i. Before the introduction of this feature, resource management was only possible through the use of profiles.

Some of the tasks that can be performed by the DRM are as follows:

• Creating resource consumer groups and limiting the number of resources on each such group (Every user application is attached with a resource consumer group, hence each application has an upper limit on the number of resources that can be allocated to it).
• Distributing the processing time by allocating percentage of CPU time to each user application (The DRM does the processing distribution in a more effective way than the operating system by allocating the CPU time on a priority basis).
• Placing an upper limit on the number of user sessions that can be concurrently executed within a resource group.
• Controlling the degree of parallelism of every transaction that are carried out by users of a resource consumer group.
• Creating an active session pool that contains the maximum number of active sessions that are specified to be concurrently active within a group of users.
• Creating an undo pool that contains undo space for consumption by a group of users.

The DRM defines the following elements for database resource management:

• Resource consumer group - A resource consumer group is a logical grouping of user sessions on the basis of the resource requirements of each user session. Hence, there can be more than one resource consumer group with each having different resource requirements. Every user session can only belong to a single resource consumer group at an instance. At times, the resource requirement of a session is not met by the resource consumer group to which it belongs. In such cases, the session can automatically switch to a different resource consumer group depending on administrator settings.
• Resource plan - A resource plan directs the distribution of resources to the resource consumer groups. There can be more than one resource plan in a database. A plan within a plan is called a subplan. Subplans can also be created through the Database Resource Manager (DRM). Subplans increase the granularity of resource distribution by directing the number of resources that can be allocated to different users of an application within a resource consumer group.
• Resource allocation method - it is a policy used by the DRM for allocating a resource to a resource consumer group or resource plan. Although several resource allocation methods are available, a user can choose a specific method that best suites his requirements.
• Resource plan directive - A resource plan directive associates each resource consumer group to a specific resource plan, and directs the number of resources that can be allocated to each resource plan. It can be created using the CREATE_PLAN_DIRECTIVE procedure of the DBMS_RESOURCE_MANAGER package.

The DRM controls the distribution of resources among the various sessions by managing the execution schedule within the database. The DRM decides which session should be allowed to run next and for how long, in accordance with the plan directive.

The use of DRM reduces the performance overhead by not switching the processes as frequently as an operating system scheduler does. The DRM also executes fewer processes concurrently and never context switches a process that is holding a latch.

The DRM controls distribution of resources among consumer groups using plan-level resource allocation methods and directives. It handles the distribution of resources among sessions belonging to consumer groups through the consumer-group methods and directives.

Rating: