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promql: Improve the rate extrapolation explanation

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Signed-off-by: beorn7 <beorn@grafana.com>
This commit is contained in:
beorn7 2024-09-03 22:09:07 +02:00
parent 282fb1632a
commit 2304be9dd5
1 changed files with 12 additions and 4 deletions
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16
promql/functions.go
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@ -130,10 +130,18 @@ func extrapolatedRate(vals []parser.Value, args parser.Expressions, enh *EvalNod
sampledInterval := float64(lastT-firstT) / 1000
averageDurationBetweenSamples := sampledInterval / float64(numSamplesMinusOne)
// If the first/last samples are close to the boundaries of the range,
// extrapolate the result. This is as we expect that another sample
// will exist given the spacing between samples we've seen thus far,
// with an allowance for noise.
// If samples are close enough to the (lower or upper) boundary of the
// range, we extrapolate the rate all the way to the boundary in
// question. "Close enough" is defined as "up to 10% more than the
// average duration between samples within the range", see
// extrapolationThreshold below. Essentially, we are assuming a more or
// less regular spacing between samples, and if we don't see a sample
// where we would expect one, we assume the series does not cover the
// whole range, but starts and/or ends within the range. We still
// extrapolate the rate in this case, but not all the way to the
// boundary, but only by half of the average duration between samples
// (which is our guess for where the series actually starts or ends).
extrapolationThreshold := averageDurationBetweenSamples * 1.1
extrapolateToInterval := sampledInterval