15.00 - Resource Accounting - Teradata Database

Teradata Database Utilities

Teradata Database
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Resource Accounting

Priority Scheduler resource accounting employs three user-settable parameters:

  • Age Time is the period of time over which Priority Scheduler measures the resource consumption of Allocation Groups in order to balance usage and priority.
  • Active Time is the period of time over which Priority Scheduler monitors the activity level of Allocation Groups. Groups with no tasks running for the length of time represented by the Active Time are removed from Priority Scheduler resource accounting for the period.
  • CPU Usage Limit is the total amount of CPU resource that can be used at any point in time by all Teradata Database sessions that are under the control of Priority Scheduler.
  • Resource use is tracked by means of a Scheduling Set data structure. There is one Scheduling Set allocated for every session.

    Age Time

    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.

    Active Time

    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:

  • Limits the total CPU resources consumed to a specified percentage value
  • Has no effect on the scheduling strategy defined by other Priority Scheduler parameters
  • Is enforced separately on individual nodes of the Teradata Database system, but is not enforced on PE-only nodes.