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Job management

Job submission limits#

You may have encountered situations where your jobs get rejected at submission with errors like this:

sbatch: error: MaxSubmitJobsPerAccount
sbatch: error: MaxSubmitJobsPerUser

There are a number of limits on Sherlock, that are put in place to guarantee that all of the users can have a fair access to resources and a smooth experience while using them. One of those limits is about the total number of jobs a single user (and a single group) can have in queue at any given time. This helps ensuring that the scheduler is able to continue operating in an optimal fashion, without being overloaded by a single user or group.

Minimizing the number of jobs in queue#

It's generally a good practice to try reducing the number of jobs submitted to the scheduler, and depending on your workflow, there are various approaches for this. One solution may be to pack more work within a single job, which could help in reducing the overall number of jobs you'll have to submit.

Imagine you have a 100-task array job, where you run 1 app task per array item, which looks like this:

#SBATCH --array=1-100
#SBATCH -n 1


This script would create 100 jobs in queue (even though they would all be regrouped under the same job array), each using 1 CPU to run 1 task.

Instead of that 100-task array job, you can try something like this:

#SBATCH --array=0-99:10
#SBATCH -n 10

for i in {0..9}; do
    srun -n 1 ./app $((SLURM_ARRAY_TASK_ID+i)) &

wait # important to make sure the job doesn't exit before the background tasks are done
  • --array=1-100:10 will use job array indexes 0, 10, 20 ... 90
  • -n 10 will make sure each job can be subdivided in 10 1-CPU steps
  • the for loop will launch 10 tasks, with indexes from SLURM_ARRAY_TASK_ID to SLURM_ARRAY_TASK_ID + 9.

This would submit a 10-task array job, each of them running 10 steps simultaneously, on the 10 CPUs that each of the job array item will be allocated.

In the end, you'll have run the same number of app instances, but you'll have divided the number of jobs submitted by 10, and allow you to submit the same amount of work to the scheduler, while staying under the submission limits.