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    DataWorks:Impact of DST on scheduled tasks

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    DataWorks:Impact of DST on scheduled tasks

    Last Updated:Jun 20, 2026

    This topic describes how daylight saving time (DST) transitions affect task instance generation and scheduled times. It also explains the DataWorks policies for handling these transitions in regions that observe DST.

    How it works

    DataWorks automatically handles DST switching to ensure tasks run correctly on transition days. The following examples for an hourly task in the US West region show how DataWorks handles the logic for DST transitions:

    • When DST begins:

      • Number of instances: DST begins at 02:00. Clocks spring forward one hour, shifting the time from 02:00 to 03:00. As a result, no instance is generated at 02:00, and an hourly task produces 23 instances on this day.

      • Instance scheduled time: This time shift adjusts the scheduled run time for some tasks. For example, the fourth instance of an hourly task, which would normally be scheduled for 04:00, is scheduled for 05:00 on the day DST begins.

      Note

      • On the day DST begins, if a daily, weekly, or monthly task is scheduled during the skipped hour, the task will not run and the system sets its instance to dry-run.

      • On this day, subtracting 10 minutes from 03:00 results in 01:50.

    • When DST ends:

      Number of instances: An hourly task generates 24 instances. Two instances are generated for the 02:00 hour, but only the instance for the second 02:00 is retained.

      Note

      On this day, subtracting 10 minutes from 03:00 results in 02:50.

    Limitations

    DST transitions only affect tasks in regions that observe daylight saving time.

    Impacts when DST begins

    Impact 1: Instance generation

    • Scenario 1: Impact on hourly and minute-level tasks.

      Consider an hourly task configured as follows. Under normal conditions, it generates one instance per hour for a total of 24 instances per day. On the day DST begins, only 23 instances are generated because the instance for 02:00 is skipped.

      Note

      DST begins at 02:00. Clocks spring forward one hour, shifting from 02:00 to 03:00. Therefore, no instance is generated at 02:00.

      The scheduling configuration is in hourly interval mode. The Start Time is 00:00, the End Time is 23:59, and the effective date is set to Always. This corresponds to the cron expression 00 00 00-23/1 * * ?.

    • Scenario 2: Impact on daily tasks.

      A daily task still generates one instance on the day DST begins, but its execution depends on the scheduled time.

      • If the scheduled time is between 02:00 and 03:00, the system delays the scheduled time by one hour and sets the instance to Empty run.

      • If the scheduled time is outside the 02:00 to 03:00 range, the task runs normally.

      In the scheduling configuration, the scheduling cycle is set to Daily, the scheduled time is 02:00, and the effective date is set to Always. This corresponds to the cron expression 00 00 02 * * ?.

    Impact 2: Parameter substitution

    • Scenario 1: If a task has a scheduled time of 03:00 and a scheduling parameter of $[hh24-1/24], the parameter value would normally resolve to 02:00. When DST begins, it resolves to 01:00.

    • Scenario 2: If a task has a scheduled time of 02:00 and a scheduling parameter of $[hh24-1/24], the parameter value would normally resolve to 01:00. When DST begins, it still resolves to 01:00. If this is a daily task, the system sets the instance for that day to dry-run.

    Impacts when DST ends

    Impact 1: Instance generation

    For an hourly task, the day DST ends is 25 hours long and includes two 02:00 hours. However, the task still generates only 24 instances, retaining only the instance from the second 02:00 hour.

    Impact 2: Parameter substitution

    On the day DST ends, the day is 25 hours long because the 02:00 hour occurs twice. An hourly task still generates only 24 instances, retaining only the instance from the second 02:00. If a task's scheduling parameters involve calculations based on the instance's scheduled time, this 25-hour day can cause offsets, as the following scenarios illustrate.

    • Scenario 1: If a task has a scheduled time of 03:00 and a scheduling parameter of $[hh24-2/24], the parameter value would normally resolve to 01:00. When DST ends, it resolves to 02:00.

    • Scenario 2: If a task has a scheduled time of 02:00 and a scheduling parameter of $[hh24-1/24], the parameter value would normally resolve to 01:00. When DST ends, it resolves to 02:00.