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feat(remote): reduce resolution of native histograms on remote read

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If a sample read through remote read has too high resolution,
reduce it to the maximum allowed.

This is a slow path, but we only expect it to happen if the server
side is newer version that allows higher resolution.

Signed-off-by: György Krajcsovits <gyorgy.krajcsovits@grafana.com>
This commit is contained in:
György Krajcsovits 2025-09-18 13:12:18 +02:00
parent 46d15c2626
commit 3e96d902e0
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GPG Key ID: 47A8F9CE80FD7C7F
2 changed files with 45 additions and 3 deletions
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20
storage/remote/codec.go
View File

@ -472,7 +472,7 @@ func (c *concreteSeriesIterator) Seek(t int64) chunkenc.ValueType {
}
func validateHistogramSchema(h *prompb.Histogram) error {
if histogram.IsValidSchema(h.Schema) {
if histogram.IsAcceptibleSchema(h.Schema) {
return nil
}
return fmt.Errorf("invalid histogram schema %d", h.Schema)
@ -500,14 +500,28 @@ func (c *concreteSeriesIterator) AtHistogram(*histogram.Histogram) (int64, *hist
panic("iterator is not on an integer histogram sample")
}
h := c.series.histograms[c.histogramsCur]
return h.Timestamp, h.ToIntHistogram()
mh := h.ToIntHistogram()
if mh.Schema > histogram.ExponentialSchemaMax && mh.Schema <= histogram.ExponentialSchemaMaxReserved {
// This is a very slow path, but it should only happen if the
// sample is from a newer Prometheus version that supports higher
// resolution.
mh.ReduceResolution(histogram.ExponentialSchemaMax)
}
return h.Timestamp, mh
}
// AtFloatHistogram implements chunkenc.Iterator.
func (c *concreteSeriesIterator) AtFloatHistogram(*histogram.FloatHistogram) (int64, *histogram.FloatHistogram) {
if c.curValType == chunkenc.ValHistogram || c.curValType == chunkenc.ValFloatHistogram {
fh := c.series.histograms[c.histogramsCur]
return fh.Timestamp, fh.ToFloatHistogram() // integer will be auto-converted.
mfh := fh.ToFloatHistogram() // integer will be auto-converted.
if mfh.Schema > histogram.ExponentialSchemaMax && mfh.Schema <= histogram.ExponentialSchemaMaxReserved {
// This is a very slow path, but it should only happen if the
// sample is from a newer Prometheus version that supports higher
// resolution.
mfh.ReduceResolution(histogram.ExponentialSchemaMax)
}
return fh.Timestamp, mfh
}
panic("iterator is not on a histogram sample")
}

28
storage/remote/codec_test.go
View File

@ -592,6 +592,34 @@ func TestConcreteSeriesIterator_InvalidHistogramSamples(t *testing.T) {
}
}
func TestConcreteSeriesIterator_ReducesHighResolutionHistograms(t *testing.T) {
for _, schema := range []int32{9, 52} {
t.Run(fmt.Sprintf("schema=%d", schema), func(t *testing.T) {
h := testHistogram.Copy()
h.Schema = schema
fh := h.ToFloat(nil)
series := &concreteSeries{
labels: labels.FromStrings("foo", "bar"),
histograms: []prompb.Histogram{
prompb.FromIntHistogram(1, h),
prompb.FromFloatHistogram(2, fh),
},
}
it := series.Iterator(nil)
require.Equal(t, chunkenc.ValHistogram, it.Next())
_, gotH := it.AtHistogram(nil)
require.Equal(t, histogram.ExponentialSchemaMax, gotH.Schema)
_, gotFH := it.AtFloatHistogram(nil)
require.Equal(t, histogram.ExponentialSchemaMax, gotFH.Schema)
require.Equal(t, chunkenc.ValFloatHistogram, it.Next())
_, gotFH = it.AtFloatHistogram(nil)
require.Equal(t, histogram.ExponentialSchemaMax, gotFH.Schema)
require.Equal(t, chunkenc.ValNone, it.Next())
require.NoError(t, it.Err())
})
}
}
func TestFromQueryResultWithDuplicates(t *testing.T) {
ts1 := prompb.TimeSeries{
Labels: []prompb.Label{