What is a difference between rollup_rate (avg) and rate in MetricsQL?

Question

As stated in title, what is a difference between avg from rollup_rate() and rate() in MetricsQL?

It is not clear to me from the official documentation.

Answer 1

Let's suppose we have a time series with the following samples on the duration d:

(v1, t1), (v2, t2), .... (vN, tN)`

Then the rate(m[d]) at tN is calculated as (vN - v1) / (tN - t1), while the avg returned from rollup_rate(m[d]) is calculated as an average value for per-sample rates (v2-v1)/(t2-t1), ..., (vN - vNminus1) / (tN - tNminus1).