Track data points with constant-space via sampling (can be used to calculate percentiles, for example)

stat.go

const (
	MAX_SAMPLE_COUNT = 50
	MAX_SAMPLE_COUNT_F = float64(MAX_SAMPLE_COUNT)
)

type Stat struct {
	sync.Mutex
	hits int64
	samples []int
}

func (s *Stat) Timing(t int) {
	index := -1
	hits := atomic.AddInt64(&s.hits, 1)
	if hits < MAX_SAMPLE_COUNT {
		index = int(hits)
	} else if MAX_SAMPLE_COUNT_F / float64(hits) > rand.Float64() {
		index = int(rand.Int31n(MAX_SAMPLE_COUNT))
	}

	if index != -1 {
		s.Lock()
		s.samples[index] = t
		s.Unlock()
	}
}