Frequently Asked Questions: Difference between revisions

Frequently Asked Questions (view source)

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 * resources needed by other, higher-priority jobs waiting to run
-Perforce, Slurm assumes
+The start times are conditional - <tt>Slurm</tt> invalidates these future plans if:
-* that time limits for running jobs are accurate, and
+* jobs end early, changing which resources become available;
-* new jobs will not arrive and perturb the priority list.
+* prioritization is perturbed: submission of higher-priority jobs or cancellation of queued jobs
-Both these assumptions are obviously wrong, the second one being perhaps the most problematic. On Compute Canada general purpose clusters, a new job is submitted on average about every five seconds, so any projection more than five seconds in the future is clearly at risk of changing.
-Most waiting jobs have a START_TIME of "N/A", which stands for "not available", meaning Slurm is not attempting to project a start time for that job.
+On Compute Canada general purpose clusters, new jobs are submitted about every five seconds, and 30-50% of jobs end early,
+so <tt>Slurm</tt> often discards and recomputes its future plans.
+Most waiting jobs have a START_TIME of "N/A", which stands for "not available", meaning <tt>Slurm</tt> is not attempting to project a start time for that job.
 For jobs which are already running, the start time reported by <tt>squeue</tt> is perfectly accurate.
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