Merge pull request #1314 from prometheus/beorn7/histogram
histogram: Enable detection of a native histogram without observations
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90b169a60d
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@ -428,12 +428,12 @@ type HistogramOpts struct {
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// a major version bump.
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NativeHistogramBucketFactor float64
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// All observations with an absolute value of less or equal
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// NativeHistogramZeroThreshold are accumulated into a “zero”
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// bucket. For best results, this should be close to a bucket
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// boundary. This is usually the case if picking a power of two. If
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// NativeHistogramZeroThreshold are accumulated into a “zero” bucket.
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// For best results, this should be close to a bucket boundary. This is
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// usually the case if picking a power of two. If
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// NativeHistogramZeroThreshold is left at zero,
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// DefNativeHistogramZeroThreshold is used as the threshold. To configure
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// a zero bucket with an actual threshold of zero (i.e. only
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// DefNativeHistogramZeroThreshold is used as the threshold. To
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// configure a zero bucket with an actual threshold of zero (i.e. only
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// observations of precisely zero will go into the zero bucket), set
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// NativeHistogramZeroThreshold to the NativeHistogramZeroThresholdZero
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// constant (or any negative float value).
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@ -446,23 +446,28 @@ type HistogramOpts struct {
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// Histogram are sufficiently wide-spread. In particular, this could be
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// used as a DoS attack vector. Where the observed values depend on
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// external inputs, it is highly recommended to set a
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// NativeHistogramMaxBucketNumber.) Once the set
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// NativeHistogramMaxBucketNumber.) Once the set
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// NativeHistogramMaxBucketNumber is exceeded, the following strategy is
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// enacted: First, if the last reset (or the creation) of the histogram
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// is at least NativeHistogramMinResetDuration ago, then the whole
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// histogram is reset to its initial state (including regular
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// buckets). If less time has passed, or if
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// NativeHistogramMinResetDuration is zero, no reset is
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// performed. Instead, the zero threshold is increased sufficiently to
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// reduce the number of buckets to or below
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// NativeHistogramMaxBucketNumber, but not to more than
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// NativeHistogramMaxZeroThreshold. Thus, if
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// NativeHistogramMaxZeroThreshold is already at or below the current
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// zero threshold, nothing happens at this step. After that, if the
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// number of buckets still exceeds NativeHistogramMaxBucketNumber, the
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// resolution of the histogram is reduced by doubling the width of the
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// sparse buckets (up to a growth factor between one bucket to the next
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// of 2^(2^4) = 65536, see above).
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// enacted:
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// - First, if the last reset (or the creation) of the histogram is at
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// least NativeHistogramMinResetDuration ago, then the whole
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// histogram is reset to its initial state (including regular
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// buckets).
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// - If less time has passed, or if NativeHistogramMinResetDuration is
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// zero, no reset is performed. Instead, the zero threshold is
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// increased sufficiently to reduce the number of buckets to or below
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// NativeHistogramMaxBucketNumber, but not to more than
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// NativeHistogramMaxZeroThreshold. Thus, if
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// NativeHistogramMaxZeroThreshold is already at or below the current
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// zero threshold, nothing happens at this step.
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// - After that, if the number of buckets still exceeds
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// NativeHistogramMaxBucketNumber, the resolution of the histogram is
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// reduced by doubling the width of the sparse buckets (up to a
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// growth factor between one bucket to the next of 2^(2^4) = 65536,
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// see above).
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// - Any increased zero threshold or reduced resolution is reset back
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// to their original values once NativeHistogramMinResetDuration has
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// passed (since the last reset or the creation of the histogram).
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NativeHistogramMaxBucketNumber uint32
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NativeHistogramMinResetDuration time.Duration
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NativeHistogramMaxZeroThreshold float64
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@ -782,6 +787,16 @@ func (h *histogram) Write(out *dto.Metric) error {
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his.ZeroCount = proto.Uint64(zeroBucket)
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his.NegativeSpan, his.NegativeDelta = makeBuckets(&coldCounts.nativeHistogramBucketsNegative)
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his.PositiveSpan, his.PositiveDelta = makeBuckets(&coldCounts.nativeHistogramBucketsPositive)
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// Add a no-op span to a histogram without observations and with
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// a zero threshold of zero. Otherwise, a native histogram would
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// look like a classic histogram to scrapers.
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if *his.ZeroThreshold == 0 && *his.ZeroCount == 0 && len(his.PositiveSpan) == 0 && len(his.NegativeSpan) == 0 {
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his.PositiveSpan = []*dto.BucketSpan{{
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Offset: proto.Int32(0),
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Length: proto.Uint32(0),
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}}
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}
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}
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addAndResetCounts(hotCounts, coldCounts)
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return nil
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@ -854,13 +869,16 @@ func (h *histogram) limitBuckets(counts *histogramCounts, value float64, bucket
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h.doubleBucketWidth(hotCounts, coldCounts)
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}
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// maybeReset resests the whole histogram if at least h.nativeHistogramMinResetDuration
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// maybeReset resets the whole histogram if at least h.nativeHistogramMinResetDuration
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// has been passed. It returns true if the histogram has been reset. The caller
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// must have locked h.mtx.
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func (h *histogram) maybeReset(hot, cold *histogramCounts, coldIdx uint64, value float64, bucket int) bool {
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func (h *histogram) maybeReset(
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hot, cold *histogramCounts, coldIdx uint64, value float64, bucket int,
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) bool {
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// We are using the possibly mocked h.now() rather than
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// time.Since(h.lastResetTime) to enable testing.
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if h.nativeHistogramMinResetDuration == 0 || h.now().Sub(h.lastResetTime) < h.nativeHistogramMinResetDuration {
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if h.nativeHistogramMinResetDuration == 0 ||
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h.now().Sub(h.lastResetTime) < h.nativeHistogramMinResetDuration {
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return false
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}
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// Completely reset coldCounts.
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@ -485,6 +485,17 @@ func TestNativeHistogram(t *testing.T) {
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factor: 1,
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want: `sample_count:3 sample_sum:6 bucket:<cumulative_count:0 upper_bound:0.005 > bucket:<cumulative_count:0 upper_bound:0.01 > bucket:<cumulative_count:0 upper_bound:0.025 > bucket:<cumulative_count:0 upper_bound:0.05 > bucket:<cumulative_count:0 upper_bound:0.1 > bucket:<cumulative_count:0 upper_bound:0.25 > bucket:<cumulative_count:0 upper_bound:0.5 > bucket:<cumulative_count:1 upper_bound:1 > bucket:<cumulative_count:2 upper_bound:2.5 > bucket:<cumulative_count:3 upper_bound:5 > bucket:<cumulative_count:3 upper_bound:10 > `, // Has conventional buckets because there are no sparse buckets.
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},
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{
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name: "no observations",
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factor: 1.1,
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want: `sample_count:0 sample_sum:0 schema:3 zero_threshold:2.938735877055719e-39 zero_count:0 `,
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},
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{
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name: "no observations and zero threshold of zero resulting in no-op span",
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factor: 1.1,
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zeroThreshold: NativeHistogramZeroThresholdZero,
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want: `sample_count:0 sample_sum:0 schema:3 zero_threshold:0 zero_count:0 positive_span:<offset:0 length:0 > `,
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},
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{
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name: "factor 1.1 results in schema 3",
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observations: []float64{0, 1, 2, 3},
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