keep only 1 nhcb in memory at at time

Signed-off-by: Jeanette Tan <jeanette.tan@grafana.com>

model/textparse/nhcbparse.go

@@ -43,8 +43,8 @@ type NhcbParser struct {
 
 	buf []byte
 
-	nhcbLabels  map[uint64]labels.Labels
-	nhcbBuilder map[uint64]convertnhcb.TempHistogram
+	lsetNhcb labels.Labels
+	tempNhcb convertnhcb.TempHistogram
 }
 
 func NewNhcbParser(p Parser, keepClassicHistograms bool) Parser {
@@ -52,8 +52,7 @@ func NewNhcbParser(p Parser, keepClassicHistograms bool) Parser {
 		parser:                p,
 		keepClassicHistograms: keepClassicHistograms,
 		buf:                   make([]byte, 0, 1024),
-		nhcbLabels:            make(map[uint64]labels.Labels),
-		nhcbBuilder:           make(map[uint64]convertnhcb.TempHistogram),
+		tempNhcb:              convertnhcb.NewTempHistogram(),
 	}
 }
 
@@ -97,8 +96,7 @@ func (p *NhcbParser) CreatedTimestamp() *int64 {
 func (p *NhcbParser) Next() (Entry, error) {
 	et, err := p.parser.Next()
 	if errors.Is(err, io.EOF) {
-		if len(p.nhcbBuilder) > 0 {
-			p.processNhcb()
+		if p.processNhcb(p.tempNhcb) {
 			return EntryHistogram, nil
 		}
 		return EntryInvalid, err
@@ -123,18 +121,18 @@ func (p *NhcbParser) handleClassicHistogramSeries(lset labels.Labels) bool {
 	case strings.HasSuffix(mName, "_bucket") && lset.Has(labels.BucketLabel):
 		le, err := strconv.ParseFloat(lset.Get(labels.BucketLabel), 64)
 		if err == nil && !math.IsNaN(le) {
-			processClassicHistogramSeries(lset, "_bucket", p.nhcbLabels, p.nhcbBuilder, func(hist *convertnhcb.TempHistogram) {
+			p.processClassicHistogramSeries(lset, "_bucket", func(hist *convertnhcb.TempHistogram) {
 				hist.BucketCounts[le] = p.value
 			})
 			return true
 		}
 	case strings.HasSuffix(mName, "_count"):
-		processClassicHistogramSeries(lset, "_count", p.nhcbLabels, p.nhcbBuilder, func(hist *convertnhcb.TempHistogram) {
+		p.processClassicHistogramSeries(lset, "_count", func(hist *convertnhcb.TempHistogram) {
 			hist.Count = p.value
 		})
 		return true
 	case strings.HasSuffix(mName, "_sum"):
-		processClassicHistogramSeries(lset, "_sum", p.nhcbLabels, p.nhcbBuilder, func(hist *convertnhcb.TempHistogram) {
+		p.processClassicHistogramSeries(lset, "_sum", func(hist *convertnhcb.TempHistogram) {
 			hist.Sum = p.value
 		})
 		return true
@@ -142,23 +140,14 @@ func (p *NhcbParser) handleClassicHistogramSeries(lset labels.Labels) bool {
 	return false
 }
 
-func processClassicHistogramSeries(lset labels.Labels, suffix string, nhcbLabels map[uint64]labels.Labels, nhcbBuilder map[uint64]convertnhcb.TempHistogram, updateHist func(*convertnhcb.TempHistogram)) {
-	m2 := convertnhcb.GetHistogramMetricBase(lset, suffix)
-	m2hash := m2.Hash()
-	nhcbLabels[m2hash] = m2
-	th, exists := nhcbBuilder[m2hash]
-	if !exists {
-		th = convertnhcb.NewTempHistogram()
-	}
-	updateHist(&th)
-	nhcbBuilder[m2hash] = th
+func (p *NhcbParser) processClassicHistogramSeries(lset labels.Labels, suffix string, updateHist func(*convertnhcb.TempHistogram)) {
+	p.lsetNhcb = convertnhcb.GetHistogramMetricBase(lset, suffix)
+	updateHist(&p.tempNhcb)
 }
 
-func (p *NhcbParser) processNhcb() {
-	for hash, th := range p.nhcbBuilder {
-		lset, ok := p.nhcbLabels[hash]
-		if !ok {
-			continue
+func (p *NhcbParser) processNhcb(th convertnhcb.TempHistogram) bool {
+	if len(th.BucketCounts) == 0 {
+		return false
 	}
 	ub := make([]float64, 0, len(th.BucketCounts))
 	for b := range th.BucketCounts {
@@ -169,20 +158,20 @@ func (p *NhcbParser) processNhcb() {
 	h, fh := convertnhcb.ConvertHistogramWrapper(th, upperBounds, hBase, fhBase)
 	if h != nil {
 		if err := h.Validate(); err != nil {
-				panic("histogram validation failed")
+			return false
 		}
 		p.h = h
 		p.fh = nil
 	} else if fh != nil {
 		if err := fh.Validate(); err != nil {
-				panic("histogram validation failed")
+			return false
 		}
 		p.h = nil
 		p.fh = fh
 	}
-		p.bytes = lset.Bytes(p.buf)
-		p.lset = lset
-		p.metricString = lset.String()
-	}
-	p.nhcbBuilder = map[uint64]convertnhcb.TempHistogram{}
+	p.bytes = p.lsetNhcb.Bytes(p.buf)
+	p.lset = p.lsetNhcb
+	p.metricString = p.lsetNhcb.String()
+	p.tempNhcb = convertnhcb.NewTempHistogram()
+	return true
 }