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app/vmselect/promql: prevent from incorrect calculations for deriv() over multiple samples with identical timestamps

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Aliaksandr Valialkin 2021-11-12 13:50:43 +02:00
parent 82917398b9
commit 82cf9f26db
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1 changed files with 6 additions and 1 deletions
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7
app/vmselect/promql/rollup.go
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@ -875,7 +875,12 @@ func linearRegression(rfa *rollupFuncArg) (float64, float64) {
tvSum += dt * v tvSum += dt * v
ttSum += dt * dt ttSum += dt * dt
} }
k := (tvSum - tSum*vSum/n) / (ttSum - tSum*tSum/n) k := float64(0)
tDiff := ttSum - tSum*tSum/n
if math.Abs(tDiff) >= 1e-6 {
// Prevent from incorrect division for too small tDiff values.
k = (tvSum - tSum*vSum/n) / tDiff
}
v := vSum/n - k*tSum/n v := vSum/n - k*tSum/n
return v, k return v, k
} }