diff --git a/storage/metric/instrumentation.go b/storage/metric/instrumentation.go
index 1dd1867aaf..8e4fdc5cf7 100644
--- a/storage/metric/instrumentation.go
+++ b/storage/metric/instrumentation.go
@@ -43,6 +43,7 @@ const (
 	hasLabelName                = "has_label_name"
 	hasLabelPair                = "has_label_pair"
 	indexMetric                 = "index_metric"
+	indexSamples                = "index_samples"
 	rebuildDiskFrontier         = "rebuild_disk_frontier"
 	renderView                  = "render_view"
 	setLabelNameFingerprints    = "set_label_name_fingerprints"
diff --git a/storage/metric/leveldb.go b/storage/metric/leveldb.go
index d50ed6d7a3..726650e073 100644
--- a/storage/metric/leveldb.go
+++ b/storage/metric/leveldb.go
@@ -199,15 +199,10 @@ func (l *LevelDBMetricPersistence) AppendSample(sample model.Sample) (err error)
 	return
 }
 
-func (l *LevelDBMetricPersistence) AppendSamples(samples model.Samples) (err error) {
-	begin := time.Now()
-	defer func() {
-		duration := time.Since(begin)
-
-		recordOutcome(duration, err, map[string]string{operation: appendSamples, result: success}, map[string]string{operation: appendSamples, result: failure})
-	}()
-
-	// Group the samples by fingerprint.
+// groupByFingerprint collects all of the provided samples, groups them
+// together by their respective metric fingerprint, and finally sorts
+// them chronologically.
+func groupByFingerprint(samples model.Samples) map[model.Fingerprint]model.Samples {
 	var (
 		fingerprintToSamples = map[model.Fingerprint]model.Samples{}
 	)
@@ -219,17 +214,18 @@ func (l *LevelDBMetricPersistence) AppendSamples(samples model.Samples) (err err
 		fingerprintToSamples[fingerprint] = samples
 	}
 
-	// Begin the sorting of grouped samples.
 	var (
 		sortingSemaphore = make(chan bool, sortConcurrency)
-		doneSorting      = sync.WaitGroup{}
+		doneSorting      sync.WaitGroup
 	)
+
 	for i := 0; i < sortConcurrency; i++ {
 		sortingSemaphore <- true
 	}
 
 	for _, samples := range fingerprintToSamples {
 		doneSorting.Add(1)
+
 		go func(samples model.Samples) {
 			<-sortingSemaphore
 			sort.Sort(samples)
@@ -240,56 +236,18 @@ func (l *LevelDBMetricPersistence) AppendSamples(samples model.Samples) (err err
 
 	doneSorting.Wait()
 
-	var (
-		doneCommitting = sync.WaitGroup{}
-	)
+	return fingerprintToSamples
+}
 
-	go func() {
-		doneCommitting.Add(1)
-		samplesBatch := leveldb.NewBatch()
-		defer samplesBatch.Close()
-		defer doneCommitting.Done()
+// indexSamples takes groups of samples, determines which ones contain metrics
+// that are unknown to the storage stack, and then proceeds to update all
+// affected indices.
+func (l *LevelDBMetricPersistence) indexSamples(groups map[model.Fingerprint]model.Samples) (err error) {
+	begin := time.Now()
+	defer func() {
+		duration := time.Since(begin)
 
-		for fingerprint, group := range fingerprintToSamples {
-			for {
-				lengthOfGroup := len(group)
-
-				if lengthOfGroup == 0 {
-					break
-				}
-
-				take := *leveldbChunkSize
-				if lengthOfGroup < take {
-					take = lengthOfGroup
-				}
-
-				chunk := group[0:take]
-				group = group[take:lengthOfGroup]
-
-				key := &dto.SampleKey{
-					Fingerprint:   fingerprint.ToDTO(),
-					Timestamp:     indexable.EncodeTime(chunk[0].Timestamp),
-					LastTimestamp: proto.Int64(chunk[take-1].Timestamp.Unix()),
-					SampleCount:   proto.Uint32(uint32(take)),
-				}
-
-				value := &dto.SampleValueSeries{}
-				for _, sample := range chunk {
-					value.Value = append(value.Value, &dto.SampleValueSeries_Value{
-						Timestamp: proto.Int64(sample.Timestamp.Unix()),
-						Value:     proto.Float32(float32(sample.Value)),
-					})
-				}
-
-				samplesBatch.Put(coding.NewProtocolBufferEncoder(key), coding.NewProtocolBufferEncoder(value))
-			}
-		}
-
-		err = l.metricSamples.Commit(samplesBatch)
-
-		if err != nil {
-			panic(err)
-		}
+		recordOutcome(duration, err, map[string]string{operation: indexSamples, result: success}, map[string]string{operation: indexSamples, result: failure})
 	}()
 
 	var (
@@ -298,7 +256,7 @@ func (l *LevelDBMetricPersistence) AppendSamples(samples model.Samples) (err err
 
 	// Determine which metrics are unknown in the database.
 
-	for fingerprint, samples := range fingerprintToSamples {
+	for fingerprint, samples := range groups {
 		sample := samples[0]
 		metricDTO := model.SampleToMetricDTO(&sample)
 		indexHas, err := l.hasIndexMetric(metricDTO)
@@ -501,7 +459,80 @@ func (l *LevelDBMetricPersistence) AppendSamples(samples model.Samples) (err err
 		}
 	}
 
+	return
+}
+
+func (l *LevelDBMetricPersistence) AppendSamples(samples model.Samples) (err error) {
+	begin := time.Now()
+	defer func() {
+		duration := time.Since(begin)
+
+		recordOutcome(duration, err, map[string]string{operation: appendSamples, result: success}, map[string]string{operation: appendSamples, result: failure})
+	}()
+
+	var (
+		fingerprintToSamples = groupByFingerprint(samples)
+		indexErrChan         = make(chan error)
+		doneCommitting       sync.WaitGroup
+	)
+
+	go func(groups map[model.Fingerprint]model.Samples) {
+		indexErrChan <- l.indexSamples(groups)
+	}(fingerprintToSamples)
+
+	go func() {
+		doneCommitting.Add(1)
+		samplesBatch := leveldb.NewBatch()
+		defer samplesBatch.Close()
+		defer doneCommitting.Done()
+
+		for fingerprint, group := range fingerprintToSamples {
+			for {
+				lengthOfGroup := len(group)
+
+				if lengthOfGroup == 0 {
+					break
+				}
+
+				take := *leveldbChunkSize
+				if lengthOfGroup < take {
+					take = lengthOfGroup
+				}
+
+				chunk := group[0:take]
+				group = group[take:lengthOfGroup]
+
+				key := &dto.SampleKey{
+					Fingerprint:   fingerprint.ToDTO(),
+					Timestamp:     indexable.EncodeTime(chunk[0].Timestamp),
+					LastTimestamp: proto.Int64(chunk[take-1].Timestamp.Unix()),
+					SampleCount:   proto.Uint32(uint32(take)),
+				}
+
+				value := &dto.SampleValueSeries{}
+				for _, sample := range chunk {
+					value.Value = append(value.Value, &dto.SampleValueSeries_Value{
+						Timestamp: proto.Int64(sample.Timestamp.Unix()),
+						Value:     proto.Float32(float32(sample.Value)),
+					})
+				}
+
+				samplesBatch.Put(coding.NewProtocolBufferEncoder(key), coding.NewProtocolBufferEncoder(value))
+			}
+		}
+
+		err = l.metricSamples.Commit(samplesBatch)
+
+		if err != nil {
+			panic(err)
+		}
+	}()
+
 	doneCommitting.Wait()
+	err = <-indexErrChan
+	if err != nil {
+		panic(err)
+	}
 
 	return
 }