increase() in Prometheus sometimes doubles values: how to avoid?

Question

I\'ve found that for some graphs I get doubles values from Prometheus where should be just ones:

Query I use:

increase(signups_count[4m])
         


        

Answer 1

This is known as aliasing and is a fundamental problem in signal processing. You can improve this a bit by increasing your sample rate, a 4m range is a bit short with a 2m range. Try a 10m range.

Here for example the query executed at 1515722220 only sees the 580@1515722085.194 and 581@1515722205.194 samples. That's an increase of 1 over 2 minutes, which extrapolated over 4 minutes is an increase of 2 - which is as expected.

Any metrics-based monitoring system will have similar artifacts, if you want 100% accuracy you need logs.