Service level thresholds enable you to compare actual service levels against required levels of service. This provides accountability for the delivery or the failure to deliver an agreed service level. The end goal is a predictable system that achieves service levels. There is no requirement to perform as fast as possible with minimum resource consumption; the requirement is to meet the quality of service.
AWR enables you to explicitly specify two performance thresholds for each service: the response time for calls (
ELAPSED_TIME_PER_CALL), and the CPU time for calls (
CPU_TIME_PER_CALL). The response time threshold indicates that the elapsed time for each user call for each service should not exceed a certain value, and the CPU time for calls threshold indicates that the time spent using the CPU for each call for each service should not exceed a certain value. Response time is a fundamental measure that reflects all delays and faults that might be blocking the call from running on behalf of the user. Response time can also indicate differences in node power across the nodes of an Oracle RAC database.
You must set these thresholds on each instance of an Oracle RAC database. The elapsed time and CPU time are calculated as the moving average of the elapsed, server-side call time. The AWR monitors the elapsed time and CPU time and publishes AWR alerts when the performance exceeds the thresholds. You can schedule actions using Oracle Enterprise Manager jobs for these alerts, or you can schedule actions to occur programmatically when the alert is received. You can respond to these alerts by changing the priority of a job, stopping overloaded processes, or by relocating, starting or stopping a service. This permits you to maintain service availability despite changes in demand.
This section includes the following topics: