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app/vmselect/promql: properly handle precision errors in rollup functions

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changes(), increases_over_time() and resets() shouldn't take into account
value changes, which may occur because of precision errors.

The maximum guaranteed precision for raw samples stored in VictoriaMetrics is 12 decimal digits.
So do not count relative changes for values if they are smaller than 1e-12 comparing to the value.

Updates https://github.com/VictoriaMetrics/VictoriaMetrics/issues/767
This commit is contained in:
Aliaksandr Valialkin 2024-02-08 02:30:55 +02:00
parent d5b9b56ae4
commit 726751a311
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16
app/vmselect/promql/rollup.go
View file

@ -1893,6 +1893,10 @@ func rollupChangesPrometheus(rfa *rollupFuncArg) float64 {
n := 0
for _, v := range values[1:] {
if v != prevValue {
if math.Abs(v-prevValue) < 1e-12*math.Abs(v) {
// This may be precision error. See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/767#issuecomment-1650932203
continue
}
n++
prevValue = v
}
@ -1916,6 +1920,10 @@ func rollupChanges(rfa *rollupFuncArg) float64 {
}
for _, v := range values {
if v != prevValue {
if math.Abs(v-prevValue) < 1e-12*math.Abs(v) {
// This may be precision error. See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/767#issuecomment-1650932203
continue
}
n++
prevValue = v
}
@ -1944,6 +1952,10 @@ func rollupIncreases(rfa *rollupFuncArg) float64 {
n := 0
for _, v := range values {
if v > prevValue {
if math.Abs(v-prevValue) < 1e-12*math.Abs(v) {
// This may be precision error. See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/767#issuecomment-1650932203
continue
}
n++
}
prevValue = v
@ -1975,6 +1987,10 @@ func rollupResets(rfa *rollupFuncArg) float64 {
n := 0
for _, v := range values {
if v < prevValue {
if math.Abs(v-prevValue) < 1e-12*math.Abs(v) {
// This may be precision error. See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/767#issuecomment-1650932203
continue
}
n++
}
prevValue = v

1
docs/CHANGELOG.md
View file

@ -14,6 +14,7 @@ The following `tip` changes can be tested by building VictoriaMetrics components
* SECURITY: upgrade Go builder from Go1.21.6 to Go1.21.7. See [the list of issues addressed in Go1.21.7](https://github.com/golang/go/issues?q=milestone%3AGo1.21.7+label%3ACherryPickApproved).
* BUGFIX: [MetricsQL](https://docs.victoriametrics.com/MetricsQL.html): properly propagate [label filters](https://docs.victoriametrics.com/keyconcepts/#filtering) from multiple arguments passed to [aggregate functions](https://docs.victoriametrics.com/metricsql/#aggregate-functions). For example, `sum({job="foo"}, {job="bar"}) by (job) + a` was improperly optimized to `sum({job="foo"}, {job="bar"}) by (job) + a{job="foo"}` before being executed. This could lead to unexpected results. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/5604).
* BUGFIX: [MetricsQL](https://docs.victoriametrics.com/MetricsQL.html): properly handle precision errors when calculating [changes](https://docs.victoriametrics.com/metricsql/#changes), [changes_prometheus](https://docs.victoriametrics.com/metricsql/#changes_prometheus), [increases_over_time](https://docs.victoriametrics.com/metricsql/#increases_over_time) and [resets](https://docs.victoriametrics.com/metricsql/#resets) functions. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/767).
## [v1.93.11](https://github.com/VictoriaMetrics/VictoriaMetrics/releases/tag/v1.93.11)