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histograms: Small code comment and code formatting improvements 

Signed-off-by: beorn7 <beorn@grafana.com>
This commit is contained in:
beorn7 2023-04-08 22:19:35 +02:00
parent 644c80d136
commit f9db3821a8
1 changed files with 32 additions and 24 deletions
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56
prometheus/histogram.go
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@ -428,12 +428,12 @@ type HistogramOpts struct {
// a major version bump.
NativeHistogramBucketFactor float64
// All observations with an absolute value of less or equal
// NativeHistogramZeroThreshold are accumulated into a “zero”
// bucket. For best results, this should be close to a bucket
// boundary. This is usually the case if picking a power of two. If
// NativeHistogramZeroThreshold are accumulated into a “zero” bucket.
// For best results, this should be close to a bucket boundary. This is
// usually the case if picking a power of two. If
// NativeHistogramZeroThreshold is left at zero,
// DefNativeHistogramZeroThreshold is used as the threshold. To configure
// a zero bucket with an actual threshold of zero (i.e. only
// DefNativeHistogramZeroThreshold is used as the threshold. To
// configure a zero bucket with an actual threshold of zero (i.e. only
// observations of precisely zero will go into the zero bucket), set
// NativeHistogramZeroThreshold to the NativeHistogramZeroThresholdZero
// constant (or any negative float value).
@ -446,23 +446,28 @@ type HistogramOpts struct {
// Histogram are sufficiently wide-spread. In particular, this could be
// used as a DoS attack vector. Where the observed values depend on
// external inputs, it is highly recommended to set a
// NativeHistogramMaxBucketNumber.) Once the set
// NativeHistogramMaxBucketNumber.) Once the set
// NativeHistogramMaxBucketNumber is exceeded, the following strategy is
// enacted: First, if the last reset (or the creation) of the histogram
// is at least NativeHistogramMinResetDuration ago, then the whole
// histogram is reset to its initial state (including regular
// buckets). If less time has passed, or if
// NativeHistogramMinResetDuration is zero, no reset is
// performed. Instead, the zero threshold is increased sufficiently to
// reduce the number of buckets to or below
// NativeHistogramMaxBucketNumber, but not to more than
// NativeHistogramMaxZeroThreshold. Thus, if
// NativeHistogramMaxZeroThreshold is already at or below the current
// zero threshold, nothing happens at this step. After that, if the
// number of buckets still exceeds NativeHistogramMaxBucketNumber, the
// resolution of the histogram is reduced by doubling the width of the
// sparse buckets (up to a growth factor between one bucket to the next
// of 2^(2^4) = 65536, see above).
// enacted:
// - First, if the last reset (or the creation) of the histogram is at
// least NativeHistogramMinResetDuration ago, then the whole
// histogram is reset to its initial state (including regular
// buckets).
// - If less time has passed, or if NativeHistogramMinResetDuration is
// zero, no reset is performed. Instead, the zero threshold is
// increased sufficiently to reduce the number of buckets to or below
// NativeHistogramMaxBucketNumber, but not to more than
// NativeHistogramMaxZeroThreshold. Thus, if
// NativeHistogramMaxZeroThreshold is already at or below the current
// zero threshold, nothing happens at this step.
// - After that, if the number of buckets still exceeds
// NativeHistogramMaxBucketNumber, the resolution of the histogram is
// reduced by doubling the width of the sparse buckets (up to a
// growth factor between one bucket to the next of 2^(2^4) = 65536,
// see above).
// - Any increased zero threshold or reduced resolution is reset back
// to their original values once NativeHistogramMinResetDuration has
// passed (since the last reset or the creation of the histogram).
NativeHistogramMaxBucketNumber uint32
NativeHistogramMinResetDuration time.Duration
NativeHistogramMaxZeroThreshold float64
@ -854,13 +859,16 @@ func (h *histogram) limitBuckets(counts *histogramCounts, value float64, bucket
h.doubleBucketWidth(hotCounts, coldCounts)
}
// maybeReset resests the whole histogram if at least h.nativeHistogramMinResetDuration
// maybeReset resets the whole histogram if at least h.nativeHistogramMinResetDuration
// has been passed. It returns true if the histogram has been reset. The caller
// must have locked h.mtx.
func (h *histogram) maybeReset(hot, cold *histogramCounts, coldIdx uint64, value float64, bucket int) bool {
func (h *histogram) maybeReset(
hot, cold *histogramCounts, coldIdx uint64, value float64, bucket int,
) bool {
// We are using the possibly mocked h.now() rather than
// time.Since(h.lastResetTime) to enable testing.
if h.nativeHistogramMinResetDuration == 0 || h.now().Sub(h.lastResetTime) < h.nativeHistogramMinResetDuration {
if h.nativeHistogramMinResetDuration == 0 ||
h.now().Sub(h.lastResetTime) < h.nativeHistogramMinResetDuration {
return false
}
// Completely reset coldCounts.