Scenario: Changing DST start or end due to time-sensitive programs

Situation

Time-sensitive programs are scheduled to run during the hour that DST starts or ends. Because that hour is skipped or repeated, time-sensitive programs might encounter unpredictable results. The following conditions can occur:

• Jobs might run twice, thus unnecessarily affecting the performance of the system.
• Jobs might not run at all; thus, work is not completed.
• Programs might retrieve the wrong time value.

Objectives

The DST start or end, depending on which is in effect, needs to be scheduled to occur during a different time frame. A different time frame is necessary because you have time-sensitive programs scheduled to run during the time frame specified for the current time zone.

The objectives for this scenario are as follows:

• To allow the time-sensitive programs to run as scheduled
• To either change the current DST start or end time to a time frame when no time-sensitive programs are scheduled to run
• To temporarily use a different time zone that has a DST start or end time frame that does not impact time-sensitive programs

Details

The system might encounter errors if a job is scheduled to run during an hour that is either skipped or repeated, or if a job is currently running, depending on whether you are starting or ending DST. For example, if DST begins at 2:00 a.m., your system time moves forward 1 hour at 2:00 a.m. In this case, the system does not recognize the hour from 2:00 a.m. to 3:00 a.m. Time-sensitive jobs cannot be scheduled to run during this hour. The same situation applies to ending DST. You cannot schedule jobs during the hour that is repeated.

If you change the DST to a time frame when no time-sensitive programs are scheduled to run, you can continue using the current time zone. However, you need to change the DST start or end time back to the original value after the DST goes into effect.

If you create a new time zone based on the current time zone, you do not need to change the current time zone's DST properties. However, after the DST time change, you need to change the time zone system value back to the original time zone.

Recovery steps

If you have jobs scheduled to run during the start or end of DST, you can delay DST or create a new time zone that uses different start and end times for DST. If you are using an IBM-supplied time zone, create a new time zone based on the supplied time zone. This ensures that you are not editing a time zone that is supplied with the system. Otherwise, delay DST by editing the time zone description.