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Job Scheduling and File Transfer

Daylight Saving Time and Job Schedulers

job schedulers and daylight saving time

Support for Daylight Saving Time (“DST”) within job schedulers varies widely. Different schedulers handle DST differently. An often-asked question of users of schedulers is “what happens during a DST event?” We strongly suggest you query your scheduler vendor and ask.

Flux provides two types of scheduling definitions – cron-style and relative time expressions. Cron-style time expressions behave in the following manner when encountering a Daylight Saving Time switch. None of the following applies to Flux’s relative time expressions (which are not impacted by DST).

  • In the spring (when time “springs forward”), any trigger set to fire between and including 2 AM to 2:59:59 AM will be skipped since the interval from 2 AM to 2:59:59 AM does not exist during the DST change.
  • In the fall (when time “falls backward”), any trigger set to fire at 2 AM will fire at the 2 AM after the DST change has occurred. It will not fire twice – i.e., the trigger does NOT FIRE at the 2 AM that would have occurred before the DST change and again at the 2 AM that occurs after falling back to 1 AM and again progressing to 2 AM).

Additional Questions and Answers:

  1. During the spring DST change when 2am becomes 3am, how does a timer trigger interact with the “late time window” and “makeup firing”? Does Flux think that 3:00am was more than an hour after 1:59am, and so if the late time window were 90 minutes or makeup firing were enabled, a trigger scheduled at 2:01am would run at or shortly after the “new” 3:00am.

    Answer: No. When Flux fires a timer trigger, Flux then looks forward in time to schedule the next firing. Because of the DST spring ahead, the time interval on the DST date 2:00:00 AM to 2:59:59 does not exist – so when Flux schedules a job ( using 0 0 1 2 as the time expression) to run at 2:01 AM on the DST date, it actually schedules the job to run on DST date + 1 day 2:01 AM. Since a timer trigger can never fire at 2:01 AM, it can not late fire either. Setting a late time window or makeup firing will have no impact in this case.

  2. During the fall DST change, will triggers scheduled to fire between 01:00 and 01:59 trigger twice. Will the 1 o’clock hour be repeated?

    Answer: No. After a timer trigger fires, Flux then schedules the trigger for its next firing. Flux always schedules into the future. So a trigger set to fire at say 1:15 AM and 1:30 AM – once fired – would reschedule for the next day at 1:15 and 1:30. The 1:15 and 1:30 firings would not be repeated during a DST fallback.

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