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perf: eliminate excessive heap allocations #10

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perf: eliminate excessive heap allocations #10

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12 changes: 9 additions & 3 deletions metric.go
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Original file line number Diff line number Diff line change
Expand Up @@ -257,7 +257,7 @@ func (h *histogram) String() string {
func (h *histogram) Reset() {
h.Lock()
defer h.Unlock()
h.bins = nil
h.bins = h.bins[:0]
h.total = 0
}

Expand All @@ -269,7 +269,12 @@ func (h *histogram) Add(n float64) {
newbin := bin{value: n, count: 1}
for i := range h.bins {
if h.bins[i].value > n {
h.bins = append(h.bins[:i], append([]bin{newbin}, h.bins[i:]...)...)
// heap optimization, append empty slot and rotate. As maxBins is small, it's much cheaper than gc
h.bins = append(h.bins, bin{})

// shift elements to make space for newbin
copy(h.bins[i+1:], h.bins[i:])
h.bins[i] = newbin
return
}
}
Expand Down Expand Up @@ -303,7 +308,8 @@ func (h *histogram) trim() {
value: (h.bins[i-1].value*h.bins[i-1].count + h.bins[i].value*h.bins[i].count) / count,
count: count,
}
h.bins = append(h.bins[:i-1], h.bins[i:]...)
copy(h.bins[i-1:], h.bins[i:]) // it's faster to copy than to allocate new slices
h.bins = h.bins[:len(h.bins)-1]
h.bins[i-1] = merged
}
}
Expand Down