Add hash collision detection

krajorama · krajorama · commit 4b89cd56b0b0 · 2025-07-30T16:37:46.000+02:00
Signed-off-by: György Krajcsovits &lt;gyorgy.krajcsovits@grafana.com&gt;
diff --git a/storage/remote/otlptranslator/prometheusremotewrite/combined_appender.go b/storage/remote/otlptranslator/prometheusremotewrite/combined_appender.go
@@ -48,7 +48,7 @@ func NewCombinedAppender(app storage.Appender, logger *slog.Logger, reg promethe
 		app:                app,
 		logger:             logger,
 		ingestCTZeroSample: ingestCTZeroSample,
-		refs:               make(map[uint64]storage.SeriesRef),
+		refs:               make(map[uint64]labelsRef),
 		samplesAppendedWithoutMetadata: promauto.With(reg).NewCounter(prometheus.CounterOpts{
 			Namespace: "prometheus",
 			Subsystem: "api",
@@ -64,20 +64,32 @@ func NewCombinedAppender(app storage.Appender, logger *slog.Logger, reg promethe
 	}
 }
 
+type labelsRef struct {
+	ref storage.SeriesRef
+	ls  modelLabels.Labels
+}
+
 type combinedAppender struct {
 	app                            storage.Appender
 	logger                         *slog.Logger
 	samplesAppendedWithoutMetadata prometheus.Counter
 	outOfOrderExemplars            prometheus.Counter
 	ingestCTZeroSample             bool
 	// Used to ensure we only update metadata and created timestamps once, and to share storage.SeriesRefs.
-	refs map[uint64]storage.SeriesRef
+	// To detect hash collision it also stores the labels.
+	// There is no overflow/conflict list, the TSDB will handle that part.
+	refs map[uint64]labelsRef
 }
 
 func (b *combinedAppender) AppendSample(_ string, rawls labels.Labels, meta metadata.Metadata, t, ct int64, v float64, es []exemplar.Exemplar) (err error) {
 	ls := modelLabels.NewFromSorted(rawls)
 	hash := ls.Hash()
-	ref, exists := b.refs[hash]
+	lref, exists := b.refs[hash]
+	ref := lref.ref
+	if exists && !modelLabels.Equal(lref.ls, ls) {
+		// Hash collision, this is a new series.
+		exists = false
+	}
 	if !exists {
 		ref, err = b.app.UpdateMetadata(0, ls, meta)
 		if err != nil {
@@ -105,14 +117,24 @@ func (b *combinedAppender) AppendSample(_ string, rawls labels.Labels, meta meta
 		}
 	}
 	ref = b.appendExemplars(ref, ls, es)
-	b.refs[hash] = ref
+	if !exists {
+		b.refs[hash] = labelsRef{
+			ref: ref,
+			ls:  ls,
+		}
+	}
 	return
 }
 
 func (b *combinedAppender) AppendHistogram(_ string, rawls labels.Labels, meta metadata.Metadata, t, ct int64, h *histogram.Histogram, es []exemplar.Exemplar) (err error) {
 	ls := modelLabels.NewFromSorted(rawls)
 	hash := ls.Hash()
-	ref, exists := b.refs[hash]
+	lref, exists := b.refs[hash]
+	ref := lref.ref
+	if exists && !modelLabels.Equal(lref.ls, ls) {
+		// Hash collision, this is a new series.
+		exists = false
+	}
 	if !exists {
 		ref, err = b.app.UpdateMetadata(0, ls, meta)
 		if err != nil {
@@ -140,7 +162,12 @@ func (b *combinedAppender) AppendHistogram(_ string, rawls labels.Labels, meta m
 		}
 	}
 	ref = b.appendExemplars(ref, ls, es)
-	b.refs[hash] = ref
+	if !exists {
+		b.refs[hash] = labelsRef{
+			ref: ref,
+			ls:  ls,
+		}
+	}
 	return
 }
 
