Submitting Array Jobs

Parameterized and repeated execution of the same set of operations that are contained in a job script is an ideal application for the array job facility of the grid engine system. Typical examples of such applications are found in the Digital Content Creation industries for tasks such as rendering. Computation of an animation is split into frames. The same rendering computation can be performed for each frame independently.

The array job facility offers a convenient way to submit, monitor, and control such applications. The grid engine system provides an efficient implementation of array jobs, handling the computations as an array of independent tasks joined into a single job. The tasks of an array job are referenced through an array index number. The indexes for all tasks span an index range for the entire array job. The index range is defined during submission of the array job by a single qsub command.

You can monitor and control an array job. For example, you can suspend, resume, or cancel an array job as a whole or by individual task or subset of tasks. To reference the tasks, the corresponding index numbers are suffixed to the job ID. Tasks are executed very much like regular jobs. Tasks can use the environment variable SGE_TASK_ID to retrieve their own task index number and to access input data sets designated for this task identifier.

Submitting an Array Job With QMON

Follow the instructions in How To Submit a Simple Job With QMON, additionally taking into account the following information.

The submission of array jobs from QMON works virtually identically to how the submission of a simple job is described in How To Submit a Simple Job With QMON. The only difference is that the Job Tasks input window that is shown in Figure 3–5 must contain the task range specification. The task range specification uses syntax that is identical to the qsub -t command. See the qsub(1) man page for detailed information about array index syntax.

For information about monitoring and controlling jobs in general, and about array jobs in particular, see Monitoring and Controlling Jobs and Monitoring and Controlling Jobs From the Command Line. See also the man pages for qstat(1), qhold(1), qrls(1), qmod(1), and qdel(1).

Array jobs offer full access to all facilities of the grid engine system that are available for regular jobs. In particular, array jobs can be parallel jobs at the same time. Array jobs also can have interdependencies with other jobs.

Array tasks cannot have interdependencies with other jobs or with other array tasks.

Submitting an Array Job From the Command Line

To submit an array job from the command line, type the qsub command with appropriate arguments.

The following is an example of how to submit an array job:

% qsub -l h_cpu=0:45:0 -t 2-10:2 render.sh data.in

The -t option defines the task index range. In this case, 2-10:2 specifies that 2 is the lowest index number, and 10 is the highest index number. Only every second index, the :2 part of the specification, is used. Thus, the array job is made up of 5 tasks with the task indices 2, 4, 6, 8, and 10. Each task requests a hard CPU time limit of 45 minutes with the -l option. Each task executes the job script render.sh once the task is dispatched and started by the grid engine system. Tasks can use SGE_TASK_ID to find their index number, which they can use to find their input data record in the data file data.in.