Function makeBucketsFromMap

prometheus/histogram.go:2006–2056

(buckets map[int]int64)

}

func makeBucketsFromMap(buckets map[int]int64) ([]*dto.BucketSpan, []int64) {
	if len(buckets) == 0 {
		return nil, nil
	}
	var ii []int
	for k := range buckets {
		ii = append(ii, k)
	}
	sort.Ints(ii)

	var (
		spans     []*dto.BucketSpan
		deltas    []int64
		prevCount int64
		nextI     int
	)

	appendDelta := func(count int64) {
		*spans[len(spans)-1].Length++
		deltas = append(deltas, count-prevCount)
		prevCount = count
	}

	for n, i := range ii {
		count := buckets[i]
		// Multiple spans with only small gaps in between are probably
		// encoded more efficiently as one larger span with a few empty
		// buckets. Needs some research to find the sweet spot. For now,
		// we assume that gaps of one or two buckets should not create
		// a new span.
		iDelta := int32(i - nextI)
		if n == 0 || iDelta > 2 {
			// We have to create a new span, either because we are
			// at the very beginning, or because we have found a gap
			// of more than two buckets.
			spans = append(spans, &dto.BucketSpan{
				Offset: proto.Int32(iDelta),
				Length: proto.Uint32(0),
			})
		} else {
			// We have found a small gap (or no gap at all).
			// Insert empty buckets as needed.
			for j := int32(0); j < iDelta; j++ {
				appendDelta(0)
			}
		}
		appendDelta(count)
		nextI = i + 1
	}
	return spans, deltas
}