Priority Scheduler resource accounting employs three user-settable parameters:
Resource use is tracked by means of a Scheduling Set data structure. There is one Scheduling Set allocated for every session.
Age Time tells Priority Scheduler how many seconds constitute “recent” in evaluating recent resource consumption. The default value for Age Time is 60 seconds. Decreasing this Age Time makes Priority Scheduler respond more quickly to changes in resource usage. This responsiveness affects the frequency and degree of changes in task (thread) priorities, and how Priority Scheduler manages resource allocation.
Note: In this case, responsiveness is not the same as query response time. Modifying Age Time does not necessarily affect query response time. You should monitor adjustments in Age Time carefully to judge their effects on Teradata Database system performance.
The default value for Active Time is 61 seconds. During this period, an Allocation Group continues to participate in relative weight calculations and resource allocations, even when no tasks are active, in anticipation of a new task being associated with the Allocation Group.
This period causes a smoothing effect in the scheduling algorithms when a few tasks are associated with an Allocation Group at interrupted intervals.
Note: If no task controlled by an Allocation Group has consumed resources within the preceding Active Time period, the Allocation Group is considered inactive. An Allocation Group and Scheduling Set are inactive when they have no active tasks during the active time interval. A Resource Partition is inactive when it has no active Allocation Group within the active time. Priority Scheduler considers only active Resource Partitions and Allocation Groups when computing the total weight used to calculate the relative weight of Resource Partitions and Allocation Groups. You should monitor adjustments to Active Time carefully to judge their effect onTeradata Database system performance.
Age Time and Active Time should be kept similar to each other. For example, if Age Time is reduced from the default of 60 to 30 seconds, change the Active Time from the default of 61 to 31.
Teradata Database System CPU Usage Limit
You can use an optional Priority Scheduler parameter to limit the total amount of CPU resources used by the Teradata Database sessions under its control. This limit does the following: