Given a counter like http_requests_total that increases over a given time range, what is the difference in calculating delta(http_requests_total[5m]) and increase(http_requests_total[5m])?
As far as I understood the documentation, delta calculates the difference between the start and end value of the time range. increase calculates the rate and then multiplies it with the time range.
But what is the actual difference? Wouldn't these two values always be the same?
Like, say I had the following values, each value is at the next second:
t0: 5
t1: 11
t2: 18
t3: 30
Then delta would be 30 - 5 = 25. The rate would be the average of the individual deltas, which would be 8.333. If I multiply this with the time range 3, then I get 25 again. So what is actually the difference between the two?
delta will fail when your counter will be reset (when it will start counting from 0 again), while increase/rate will detect that and adjust result accordingly.
So with:
t0: 5
t1: 11
t2: 28
t3: 4
t4: 40
with delta you'll probably get 40 - 5 = 35, while increase will probably calculate something similar to (28-5)+40 = 63