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app/vmselect/promql: return expected results from increase() over the beginning of time series, which start from big value

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Examples for such counters: OS-level counters for network or cpu stats.
This commit is contained in:
Aliaksandr Valialkin 2020-01-28 16:29:48 +02:00
parent 11c03328ae
commit b28c9a3944
1 changed files with 12 additions and 4 deletions
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16
app/vmselect/promql/rollup.go
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@ -1157,10 +1157,18 @@ func rollupDeltaInternal(rfa *rollupFuncArg, canUseRealPrevValue bool) float64 {
if len(values) == 0 { if len(values) == 0 {
return nan return nan
} }
// Assume that the previous non-existing value was 0. // Assume that the previous non-existing value was 0
prevValue = 0 // only if the first value is quite small.
if canUseRealPrevValue && !math.IsNaN(rfa.prevValue) { // This should prevent from improper increase() results for os-level counters
prevValue = rfa.prevValue // such as cpu time or bytes sent over the network interface.
// These counters may start long ago before the first value appears in the db.
if values[0] < 1e6 {
prevValue = 0
if canUseRealPrevValue && !math.IsNaN(rfa.realPrevValue) {
prevValue = rfa.realPrevValue
}
} else {
prevValue = values[0]
} }
} }
if len(values) == 0 { if len(values) == 0 {