don't use cache for nhcb maps

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

scrape/scrape.go

@@ -887,9 +887,6 @@ type scrapeCache struct {
 	metadata map[string]*metaEntry
 
 	metrics *scrapeMetrics
-
-	nhcbLabels  map[uint64]labels.Labels
-	nhcbBuilder map[uint64]convertnhcb.TempHistogram
 }
 
 // metaEntry holds meta information about a metric.
@@ -913,8 +910,6 @@ func newScrapeCache(metrics *scrapeMetrics) *scrapeCache {
 		seriesPrev:    map[uint64]labels.Labels{},
 		metadata:      map[string]*metaEntry{},
 		metrics:       metrics,
-		nhcbLabels:    map[uint64]labels.Labels{},
-		nhcbBuilder:   map[uint64]convertnhcb.TempHistogram{},
 	}
 }
 
@@ -1118,11 +1113,6 @@ func (c *scrapeCache) LengthMetadata() int {
 	return len(c.metadata)
 }
 
-func (c *scrapeCache) resetNhcb() {
-	c.nhcbLabels = map[uint64]labels.Labels{}
-	c.nhcbBuilder = map[uint64]convertnhcb.TempHistogram{}
-}
-
 func newScrapeLoop(ctx context.Context,
 	sc scraper,
 	l log.Logger,
@@ -1500,6 +1490,8 @@ func (sl *scrapeLoop) append(app storage.Appender, b []byte, contentType string,
 		e               exemplar.Exemplar // escapes to heap so hoisted out of loop
 		meta            metadata.Metadata
 		metadataChanged bool
+		nhcbLabels      map[uint64]labels.Labels
+		nhcbBuilder     map[uint64]convertnhcb.TempHistogram
 	)
 
 	exemplars := make([]exemplar.Exemplar, 1)
@@ -1529,6 +1521,11 @@ func (sl *scrapeLoop) append(app storage.Appender, b []byte, contentType string,
 	// Take an appender with limits.
 	app = appender(app, sl.sampleLimit, sl.bucketLimit, sl.maxSchema)
 
+	if sl.convertClassicHistograms {
+		nhcbLabels = make(map[uint64]labels.Labels)
+		nhcbBuilder = make(map[uint64]convertnhcb.TempHistogram)
+	}
+
 	defer func() {
 		if err != nil {
 			return
@@ -1666,16 +1663,16 @@ loop:
 					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", sl.cache, func(hist *convertnhcb.TempHistogram) {
+							processClassicHistogramSeries(lset, "_bucket", nhcbLabels, nhcbBuilder, func(hist *convertnhcb.TempHistogram) {
 								hist.BucketCounts[le] = val
 							})
 						}
 					case strings.HasSuffix(mName, "_count"):
-						processClassicHistogramSeries(lset, "_count", sl.cache, func(hist *convertnhcb.TempHistogram) {
+						processClassicHistogramSeries(lset, "_count", nhcbLabels, nhcbBuilder, func(hist *convertnhcb.TempHistogram) {
 							hist.Count = val
 						})
 					case strings.HasSuffix(mName, "_sum"):
-						processClassicHistogramSeries(lset, "_sum", sl.cache, func(hist *convertnhcb.TempHistogram) {
+						processClassicHistogramSeries(lset, "_sum", nhcbLabels, nhcbBuilder, func(hist *convertnhcb.TempHistogram) {
 							hist.Sum = val
 						})
 					}
@@ -1802,9 +1799,8 @@ loop:
 		})
 	}
 
-	if sl.convertClassicHistograms {
+	for hash, th := range nhcbBuilder {
-		for hash, th := range sl.cache.nhcbBuilder {
+		lset, ok := nhcbLabels[hash]
-			lset, ok := sl.cache.nhcbLabels[hash]
 		if !ok {
 			continue
 		}
@@ -1815,7 +1811,6 @@ loop:
 		upperBounds, hBase := convertnhcb.ProcessUpperBoundsAndCreateBaseHistogram(ub, false)
 		fhBase := hBase.ToFloat(nil)
 		h, fh := convertnhcb.ConvertHistogramWrapper(th, upperBounds, hBase, fhBase)
-			// fmt.Printf("FINAL lset: %s, timestamp: %v, val: %v\n", lset, defTime, fh)
 		if h != nil {
 			if err := h.Validate(); err != nil {
 				continue
@@ -1832,22 +1827,20 @@ loop:
 			}
 		}
 	}
-		sl.cache.resetNhcb()
-	}
 
 	return
 }
 
-func processClassicHistogramSeries(lset labels.Labels, suffix string, cache *scrapeCache, updateHist func(*convertnhcb.TempHistogram)) {
+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()
-	cache.nhcbLabels[m2hash] = m2
+	nhcbLabels[m2hash] = m2
-	th, exists := cache.nhcbBuilder[m2hash]
+	th, exists := nhcbBuilder[m2hash]
 	if !exists {
 		th = convertnhcb.NewTempHistogram()
 	}
 	updateHist(&th)
-	cache.nhcbBuilder[m2hash] = th
+	nhcbBuilder[m2hash] = th
 }
 
 // Adds samples to the appender, checking the error, and then returns the # of samples added,