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beorn7 7f912db15a promql: Fix limiting of extrapolation to negative values ... This is a bit tough to explain, but I'll try: `rate` & friends have a sophisticated extrapolation algorithm. Usually, we extrapolate the result to the total interval specified in the range selector. However, if the first sample within the range is too far away from the beginning of the interval, or if the last sample within the range is too far away from the end of the interval, we assume the series has just started half a sampling interval before the first sample or after the last sample, respectively, and shorten the extrapolation interval correspondingly. We calculate the sampling interval by looking at the average time between samples within the range, and we define "too far away" as "more than 110% of that sampling interval". However, if this algorithm leads to an extrapolated starting value that is negative, we limit the start of the extrapolation interval to the point where the extrapolated starting value is zero. At least that was the intention. What we actually implemented is the following: If extrapolating all the way to the beginning of the total interval would lead to an extrapolated negative value, we would only extrapolate to the zero point as above, even if the algorithm above would have selected a starting point that is just half a sampling interval before the first sample and that starting point would not have an extrapolated negative value. In other word: What was meant as a _limitation_ of the extrapolation interval yielded a _longer_ extrapolation interval in this case. There is an exception to the case just described: If the increase of the extrapolation interval is more than 110% of the sampling interval, we suddenly drop back to only extrapolate to half a sampling interval. This behavior can be nicely seen in the testcounter_zero_cutoff test, where the rate goes up all the way to 0.7 and then jumps back to 0.6. This commit changes the behavior to what was (presumably) intended from the beginning: The extension of the extrapolation interval is only limited if actually needed to prevent extrapolation to negative values, but the "limitation" never leads to _more_ extrapolation anymore. The difference is subtle, and probably it never bothered anyone. However, if you calculate a rate of a classic histograms, the old behavior might create non-monotonic histograms as a result (because of the jumps you can see nicely in the old version of the testcounter_zero_cutoff test). With this fix, that doesn't happen anymore. Signed-off-by: beorn7 <beorn@grafana.com>		2 years ago
..
aggregators.test	address comment	4 years ago
at_modifier.test	PromQL: Test negative offset in PromQL tests	4 years ago
collision.test	promql: Organize legacy tests into appropriate files (#7989)	5 years ago
functions.test	promql: Fix limiting of extrapolation to negative values	2 years ago
histograms.test	add doc	4 years ago
literals.test	PromQL: Fix string and parentheses handling in engine (#6612)	6 years ago
native_histograms.test	promql: add histogram_avg function (#13467)	2 years ago
operators.test	Drop metric name for "atan2" binary operator	2 years ago
selectors.test	PromQL: Test negative offset in PromQL tests	4 years ago
staleness.test	Remove 4 interval staleness heuristic. (#3244)	8 years ago
subquery.test	PromQL: Fix string and parentheses handling in engine (#6612)	6 years ago
trig_functions.test	Add inverse hyperbolic functions	4 years ago