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Merged
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Feb 20, 2015
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Use binary search to pick bucket. #79

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18 changes: 13 additions & 5 deletions prometheus/histogram.go
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Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,7 @@ import (
"fmt"
"hash/fnv"
"math"
"sort"
"sync/atomic"

"github.com/golang/protobuf/proto"
Expand Down Expand Up @@ -231,11 +232,18 @@ func (h *histogram) Desc() *Desc {
}

func (h *histogram) Observe(v float64) {
for i, upperBound := range h.upperBounds {
if v <= upperBound {
atomic.AddUint64(&h.counts[i], 1)
break
}
// TODO(beorn7): For small numbers of buckets (<30), a linear search is
// slightly faster than the binary search. If we really care, we could
// switch from one search strategy to the other depending on the number
// of buckets.
//
// Microbenchmarks (BenchmarkHistogramNoLabels):
// 11 buckets: 38.3 ns/op linear - binary 48.7 ns/op
// 100 buckets: 78.1 ns/op linear - binary 54.9 ns/op
// 300 buckets: 154 ns/op linear - binary 61.6 ns/op
i := sort.SearchFloat64s(h.upperBounds, v)
if i < len(h.counts) {
atomic.AddUint64(&h.counts[i], 1)
}
atomic.AddUint64(&h.count, 1)
for {
Expand Down