While that sounds like a good idea, it's going to produce less accurate results for most use cases.
On Sat, Nov 21, 2020 at 3:15 PM Aliaksandr Valialkin <[email protected]> wrote: > 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 > <https://groups.google.com/d/msgid/prometheus-users/CAPbKnmAMMFA3gsTAbqVC5uz%3Dp-kymL3QT31vb9G3vOhemjWCfw%40mail.gmail.com?utm_medium=email&utm_source=footer> > . > -- 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/CABbyFmprYUL4BbT2UA8O%2BE_tX9wnkd8goZ8UUKJxPASwwGnWig%40mail.gmail.com.
