Impact of DST change on Qlik Compose for Data Warehouses
This topic describes how Qlik Compose for Data Warehouses is affected by Daylight Saving Time (DST) and provides guidelines for handling changes brought about by DST.
There are two types of DST changes:
- DST On - Occurs approximately when Summer starts (actual date is country specific). Its impact on local time is that local time is moved one hour forward (so, for example, 01:00AM becomes 02:00AM). This DST change does not impact Qlik Compose for Data Warehouses as it does not result in time overlap.
- DST Off - Occurs approximately when Winter starts (actual date is country specific). Its impact on local time is that local time is moved back one hour (so, for example, 02:00AM becomes 01:00AM). This DST change results in time overlap where local time travels over the same hour twice in a row.
The comments below assume that the customer has not changed the time but rather the timezone or the DST setting. Changing the actual time (not for minor time adjustments) is a sensitive operation and is best done when Qlik Compose for Data Warehouses is stopped.
There are two places where DST may have an effect:
- Timestamps in logs and audit messages are in local time. As a result, when Winter time starts, the logs will show the time going back an hour; conversely, when Summer time starts, the logs may appear to be missing one hour.
- Statistics shown on the console are also sensitive to local time, and thus may also show confusing/inaccurate data in the overlap period (going in to Winter time) or for the skipped period (going into Summer time).
In general, it is recommended to avoid non-critical task design changes during the first overlap period (going in to Winter time) so as to prevent confusion about when the changes took place.
In addition to Qlik Compose for Data Warehouses, other components are also affected including:
- The source endpoint system
- The target endpoint system
- The local operating system
- The task design (specifically using timestamp based variables)
Given the complexity of the topic and the involvement of many independent components and settings, Qlik generally recommends that customers first verify the impact of DST changes in their test environment.