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fix(promql): histogram_count inconsistent

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The problem is in the counter reset detection. The code that loads the
samples is matrixIterSlice which uses the typed Buffer iterator, which
will preload the integer histogram samples, however the last sample is
always(!) loaded as a float histogram sample in matrixIterSlice and the
optimized iterator fails to detect counter resets in that case.

Also the iterator does not reset lastH, lastFH properly.

Ref: https://github.com/prometheus/prometheus/issues/16681

Signed-off-by: György Krajcsovits <gyorgy.krajcsovits@grafana.com>
This commit is contained in:
György Krajcsovits 2025-06-03 12:17:39 +02:00
parent e6b838391a
commit df94ecebab
No known key found for this signature in database
GPG Key ID: 47A8F9CE80FD7C7F
2 changed files with 51 additions and 5 deletions
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15
promql/histogram_stats_iterator.go
View File

@ -105,6 +105,7 @@ func (f *histogramStatsIterator) AtFloatHistogram(fh *histogram.FloatHistogram)
}
func (f *histogramStatsIterator) setLastH(h *histogram.Histogram) {
f.lastFH = nil
if f.lastH == nil {
f.lastH = h.Copy()
} else {
@ -113,6 +114,7 @@ func (f *histogramStatsIterator) setLastH(h *histogram.Histogram) {
}
func (f *histogramStatsIterator) setLastFH(fh *histogram.FloatHistogram) {
f.lastH = nil
if f.lastFH == nil {
f.lastFH = fh.Copy()
} else {
@ -125,7 +127,13 @@ func (f *histogramStatsIterator) getFloatResetHint(hint histogram.CounterResetHi
return hint
}
if f.lastFH == nil {
return histogram.NotCounterReset
// If there was no previous histogram, this will not be used,
// and if there was a previous integer histogram, this will
// force a reset detection. The later can happen if we used the
// iterator to read integer histograms before, but switched to
// float histograms for whatever reason.
// https://github.com/prometheus/prometheus/issues/16681
return histogram.UnknownCounterReset
}
if f.currentFH.DetectReset(f.lastFH) {
@ -139,7 +147,10 @@ func (f *histogramStatsIterator) getResetHint(h *histogram.Histogram) histogram.
return h.CounterResetHint
}
if f.lastH == nil {
return histogram.NotCounterReset
// If there was no previous histogram, this will not be used,
// and if there was a previous float histogram, this will
// force a reset detection.
return histogram.UnknownCounterReset
}
fh, prevFH := h.ToFloat(nil), f.lastH.ToFloat(nil)

41
promql/histogram_stats_iterator_test.go
View File

@ -68,7 +68,7 @@ func TestHistogramStatsDecoding(t *testing.T) {
tsdbutil.GenerateTestHistogramWithHint(1, histogram.UnknownCounterReset),
},
expectedHints: []histogram.CounterResetHint{
histogram.NotCounterReset,
histogram.UnknownCounterReset,
},
},
{
@ -78,7 +78,7 @@ func TestHistogramStatsDecoding(t *testing.T) {
tsdbutil.GenerateTestHistogramWithHint(1, histogram.UnknownCounterReset),
},
expectedHints: []histogram.CounterResetHint{
histogram.NotCounterReset,
histogram.UnknownCounterReset,
histogram.CounterReset,
},
},
@ -90,7 +90,7 @@ func TestHistogramStatsDecoding(t *testing.T) {
tsdbutil.GenerateTestHistogramWithHint(1, histogram.UnknownCounterReset),
},
expectedHints: []histogram.CounterResetHint{
histogram.NotCounterReset,
histogram.UnknownCounterReset,
histogram.UnknownCounterReset,
histogram.CounterReset,
},
@ -141,6 +141,41 @@ func TestHistogramStatsDecoding(t *testing.T) {
}
}
func TestHistogramStatsMixedUse(t *testing.T) {
histograms := []*histogram.Histogram{
tsdbutil.GenerateTestHistogramWithHint(2, histogram.UnknownCounterReset),
tsdbutil.GenerateTestHistogramWithHint(4, histogram.UnknownCounterReset),
tsdbutil.GenerateTestHistogramWithHint(0, histogram.UnknownCounterReset),
}
series := newHistogramSeries(histograms)
it := series.Iterator(nil)
statsIterator := NewHistogramStatsIterator(it)
expectedHints := []histogram.CounterResetHint{
histogram.UnknownCounterReset,
histogram.NotCounterReset,
histogram.UnknownCounterReset,
}
actualHints := make([]histogram.CounterResetHint, 3)
typ := statsIterator.Next()
require.Equal(t, chunkenc.ValHistogram, typ)
_, h := statsIterator.AtHistogram(nil)
actualHints[0] = h.CounterResetHint
typ = statsIterator.Next()
require.Equal(t, chunkenc.ValHistogram, typ)
_, h = statsIterator.AtHistogram(nil)
actualHints[1] = h.CounterResetHint
typ = statsIterator.Next()
require.Equal(t, chunkenc.ValHistogram, typ)
_, fh := statsIterator.AtFloatHistogram(nil)
actualHints[2] = fh.CounterResetHint
require.Equal(t, chunkenc.ValNone, statsIterator.Next())
require.Equal(t, expectedHints, actualHints)
}
type histogramSeries struct {
histograms []*histogram.Histogram
}