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The Daylight Saving Time (DST) Safe Kernel avoids problems due to the switch from summer to winter time. This switch can cause problems because the clocks are set back by one hour, which means that an hour is repeated. For programs that use timestamps, this can cause the following problems:

  • Timestamps from different real times can have the same value.

  • Timestamps do not necessarily reflect the sequence in which system events really occurred.

    Note Note

    Programs that use timestamps based on Coordinated Universal Time (UTC) are not affected by this problem.

    Since not all timestamps in the SAP system are based on UTC, SAP has up till now recommended that you bring down the system, to avoid the problems described above.

    End of the note.

For more information, see SAP Note 7417.

Features

Time during the “repeated hour” runs at half the usual speed. This means that the system can rely on timestamps in the correct sequence without duplicates, even if it is not using UTC. As shown in the graphic below, the SAP system time can differ from official time by up to 30 minutes during the repeated hour.

This graphic is explained in the accompanying text.

The result is that – even if you are using local time – you do not normally need to bring down your SAP system during the switch from summer to winter time.

Recommendation Recommendation

If you have special requirements and anticipate problems with how DST works, you can switch it off, as described in Note 102088. The disadvantage is that your systems are then down for at least one hour during the seasonal switch.

End of the recommendation.