There is an alternative solution - to use the increase() function from MetricsQL - it doesn't extrapolate results and it takes into account the previous value before the window in square brackets. So it returns exact expected values. See more details at https://victoriametrics.github.io/MetricsQL.html
On Fri, Nov 20, 2020 at 2:49 PM [email protected] <[email protected]> wrote: > On Friday, 20 November 2020 at 02:29:12 UTC [email protected] wrote: > >> *Query*: >> 1. normal query: error_counter_something{job=“monitor”, device=“dev0”, >> serial=“xxxxxxxx”} >> 2. delta query: delta(error_counter_something{job=“monitor”, >> device=“dev0”, serial=“xxxxxxxx”}[$__interval] > 0) >> >> *Time Range*: 2020-11-19 16:16:00 ~ 2020-11-19 16:20:00 with 15sec >> interval >> >> *result* >> >> 16:16:15~30 raise 2 errors on device and move that error counter value >> from 7616 to 7618, >> but the delta query shows result of 3 >> >> time , delta , >> normal >> 2020-11-19 16:16:00, , 7616 >> 2020-11-19 16:16:15, , 7616 >> 2020-11-19 16:16:30, 3, 7618 >> 2020-11-19 16:16:45, , 7618 >> 2020-11-19 16:17:00, , 7618 >> (keep these value until end of query time range) >> >> > See https://prometheus.io/docs/prometheus/latest/querying/functions/#delta > *"delta(v range-vector) calculates the difference between the first and > last value of each time series element in a range vector v, returning an > instant vector with the given deltas and equivalent labels. The delta is > extrapolated to cover the full time range as specified in the range vector > selector, so that it is possible to get a non-integer result even if the > sample values are all integers."* > > You haven't said what $__interval expands to in your query. It must be at > least 30 seconds, because otherwise you wouldn't have two values in your > range vector. > > So let's see what happens with 30 seconds. The window contains two values: > > [...X........X...] > 7616 7618 > <--15s--> > > The difference between these is 2, and the time interval between them is > 15 seconds. However this increase is then extrapolated to cover the whole > window period of 30 seconds, so the value returned by delta() would be 4. > > What about if $__interval was 45 seconds? Then you'd have three values, > the difference between the first and last is 2, the time difference is 30 > seconds extrapolated to 45 seconds, so the result would be 2 x (45/30) = 3. > > If you want the actual difference between the metric now and the metric > some time ago, you can do : > > something - something offset 15s > > However, both that expression and delta() will give you nonsense values if > a counter resets, because it will jump back down towards zero and give you > a large negative value. > > Better: > > (something - something offset 15s) >= 0 > > but it won't handle counter resets as well as rate() or increase() can. > > -- > You received this message because you are subscribed to the Google Groups > "Prometheus Users" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/prometheus-users/f75b2007-96ed-4c66-b719-602934827cd3n%40googlegroups.com > <https://groups.google.com/d/msgid/prometheus-users/f75b2007-96ed-4c66-b719-602934827cd3n%40googlegroups.com?utm_medium=email&utm_source=footer> > . > -- Best Regards, Aliaksandr Valialkin, CTO VictoriaMetrics -- You received this message because you are subscribed to the Google Groups "Prometheus Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/prometheus-users/CAPbKnmAMMFA3gsTAbqVC5uz%3Dp-kymL3QT31vb9G3vOhemjWCfw%40mail.gmail.com.
