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Add a cron-like real time scheduling mode? #3188

hjoliver opened this issue Jun 10, 2019 · 1 comment


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commented Jun 10, 2019

I described (or attempted to) the difference between date-time cycling and real time scheduling, and (conceptually) how to force Cylc to do the latter, in this Discourse post (and the one before it):

If you really only need cron-like real-time scheduling, e.g. to replace a crontab with a Cylc suite, then this is unnecessarily difficult because it requires an understanding of date-time cycling, and how to tie the cycle down onto a real time schedule.

A new real time scheduling mode would make this much easier:

  • graph recurrence relations would define a real time schedule
    • (not just date-time cycle point labels for tasks, as now)
  • no need to set initial cycle point - it is always the next real time schedule point beyond "now" (at suite start-up).
  • every task would automatically get a zero-offset @wall_clock trigger
    • (this is what makes the cycle/recurrence into a real time schedule)
    • (strictly speaking only the first task(s) at the top of the workflow need a clock trigger, but it's easier to give to all tasks - which has the same effect, and should be efficient with shared xtriggers).

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commented Jun 10, 2019

If I haven't missed something important, this would be useful - e.g. to replace crontabs quite easily even if you have a tenuous grip on concept of date-time cycling.

My main concern is that many users (particularly those with no NWP background) might use real time scheduling for everything, even where cycling would be more appropriate and powerful, simply because real time scheduling is easier to understand. But, we can try to document and explain better...

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