To ensure that the data remains accessible to users, Teradata Database enforces limits on the quantity of system resources that can be used by extract and load utilities. These limits affect use of the following operators:
Each time one of these operators is referenced in an APPLY statement counts as one task. Limits are controlled by two DBSControl settings:
The system counts the total number of tasks attempting to run concurrently and then the settings of the two fields are applied to that total, and task limits are enforced, where necessary.
To get a general idea of total concurrent Teradata PT tasks for your site, consider the following basic rules:
- Each operator specified in an APPLY statement that interfaces with the Teradata Database constitutes one task. For example:
- A job that moves data between a Teradata Database and either a second, separate Teradata Database or an external source or target requires only one task, because only a single operator interfaces with each Teradata Database at one time.
- A job that moves data within a single Teradata Database requires two tasks, because both the extract and load operators interface with the database at the same time.
Keep in mind that job steps within a single job execute sequentially, so the maximum number of concurrent tasks in a single job is two.
- If more than one job script is running concurrently, the total number of tasks applied to the MaxLoad calculations is based on the total number of operators that run concurrently in all jobs.
- Default MaxLoad settings allow concurrent execution of approximately 15 tasks, so you may need to reset the MaxLoad values.
Actual limits are subject to additional factors. For details on how to set the MaxLoadAWT and MaxLoadTasks fields in the DBSControl GDO, and how those settings will affect Teradata PT jobs, see the section on the DBSControl utility in Utilities (B035-1102).