Overview - Teradata Database

Overview

Priority Scheduler consists of the following three-tiered control structure to group user sessions for scheduling purposes:

Resource Partition

Performance Group

Allocation Group

Each of these components includes parameters that relate them to each other. You define and associate these components to design an environment that favors or inhibits the performance of individual sessions based on their logon account attributes.

The following figure shows the hierarchical structure of Priority Scheduler.

The following table briefly summarizes the components of Priority Scheduler.

Component	Descriptions
Resource Partition	A Resource Partition is a collection of prioritized Performance Groups. A Resource Partition carries a weight that will be compared to other Resource Partition weights. A Resource Partition can limit the total amount of CPU used by sessions assigned to its Performance Groups. Priority Scheduler provides Resource Partition zero as the default partition. You can define four additional Resource Partitions.
Performance Group	You define Performance Groups within each additional Resource Partition. The Performance Group name matches an entry in the account ID string, which is used for logons and stored in the AccountName column of the user record in the data dictionary. Each Performance Group name must be unique.
Performance Period	You must define at least one Performance Period, but you can have up to eight Performance Periods per Performance Group. A Performance Period links a Performance Group to an Allocation Group. Optionally, a Performance Period allows you to change Allocation Group assignments based on time-of-day or resource usage.
Allocation Group	An Allocation Group carries a weight that will be compared to other Allocation Group weights. An Allocation Group can limit the total amount of CPU used by sessions under its control. Several Performance Groups within a single Resource Partition might share the same Allocation Group.

Every Teradata Database logon session is assigned to a Performance Group. Performance Groups control the prioritization of jobs started by sessions under their control. When a Performance Group is defined, it is assigned to a Resource Partition.

Each Resource Partition has a “weight” that determines the proportion of resources available to it relative to the other defined Resource Partitions. More resources are made available to Resource Partitions with higher weights. These weights participate in determining the priorities of Teradata Database jobs.

Allocation Groups are also associated with Performance Groups. Like Resource Partitions, Allocation Groups have weights that determine the proportion of resources allocated to jobs under their control, relative to the other Allocation Groups that are active within the same Resource Partition.

The combination of Resource Partition and Allocation Group parameters, acting through their common Performance Groups, determines the precise priorities of jobs running on Teradata Database.

Each Performance Group is associated with one Allocation Group at any time, however, as an option, a Performance Group's Allocation Group can change as system conditions change. Consequently, the jobs controlled by a Performance Group may have different priorities assigned to them at different times, and their priorities can change as the jobs run.

The association between a Performance Group and an Allocation Group is mediated by the Performance Group's Performance Periods. Performance Periods link Performance Groups to Allocation Groups. As an option, the Allocation Group associated with a Performance group can be dynamically changed based on current resource usage or time of day. A Performance Group can define from one to eight Performance Periods, however the most common approach is to define only a single Performance Period per Performance Group.

For more information on Priority Scheduler components, see the following:

“Resource Partitions” on page 705

“Performance Groups” on page 707

“Performance Periods” on page 710

“Allocation Groups” on page 715

To configure Priority Scheduler, see “Schmon Utility (schmon) (SLES 10 only)” on page 725.