Scheduled Queries and Daylight Saving Time¶
Alation Cloud Service Applies to Alation Cloud Service instances of Alation
Customer Managed Applies to customer-managed instances of Alation
Before the Alation 4.18 release, scheduled queries suffered the following bugs related to daylight saving time (DST):
Following the end of US DST (during autumn in the northern hemisphere), a scheduled query would run twice – an hour early and also at the correct, anticipated time – the first time it ran on standard time in a given year.
Following the start of US DST, a scheduled query would execute an hour late the first time it ran on daylight time in a given year.
Though these bugs are fixed as of 4.18, the behavior for hourly queries
going forward is noteworthy: these queries will be skipped during the
last hour of DST depending on the configured delay tolerance for
scheduled queries (alation.query_exec.scheduling.delay_tolerance);
queries during this hour will appear to Alation to be delayed at least
an hour and the delay tolerance must be greater than an hour to allow
them to run. For example, on the morning that DST ends in the U.S., a
query that is scheduled to execute on the half hour will not run at 1:30
a.m. daylight time – if the configured delay tolerance is less than 1
hour – but will run at 1:30 a.m. standard time, an hour later.
Effectively, the query will appear to run once an hour nominally,
instead of every 60 minutes, on that particular day.