I want to create alerts based on the standard deviation (
stddev) of a query. The query uses default GROUP BY function,
time($__inteval), and the alert is condition is
avg() of query(A, 1m, now).
Through trial-and-error I’ve learned the query fails because the default GROUP BY function
time($__interval) chooses intervals shorter than my acquisition rate. That means the alert evaluation always fails because the standard deviation of a single point (or no points) is null.
My solution is to specify
Min time interval = 2*(acquisition rate) to ensure the returned queries always contain at least two points… but that seems hacky.
Is there a better way to ensure
stddev() evaluates on a two or more points, so it does not produce false null data alerts?