diff --git a/cmd/prometheus/main.go b/cmd/prometheus/main.go
index 4c59aa7b5..964b0165c 100644
--- a/cmd/prometheus/main.go
+++ b/cmd/prometheus/main.go
@@ -1105,12 +1105,10 @@ func (s *readyStorage) Appender(ctx context.Context) storage.Appender {
 
 type notReadyAppender struct{}
 
-func (n notReadyAppender) Add(l labels.Labels, t int64, v float64) (uint64, error) {
+func (n notReadyAppender) Append(ref uint64, l labels.Labels, t int64, v float64) (uint64, error) {
 	return 0, tsdb.ErrNotReady
 }
 
-func (n notReadyAppender) AddFast(ref uint64, t int64, v float64) error { return tsdb.ErrNotReady }
-
 func (n notReadyAppender) Commit() error { return tsdb.ErrNotReady }
 
 func (n notReadyAppender) Rollback() error { return tsdb.ErrNotReady }
diff --git a/cmd/prometheus/main_test.go b/cmd/prometheus/main_test.go
index eb3049e11..7571234c4 100644
--- a/cmd/prometheus/main_test.go
+++ b/cmd/prometheus/main_test.go
@@ -265,11 +265,11 @@ func TestTimeMetrics(t *testing.T) {
 	))
 
 	app := db.Appender(context.Background())
-	_, err = app.Add(labels.FromStrings(model.MetricNameLabel, "a"), 1000, 1)
+	_, err = app.Append(0, labels.FromStrings(model.MetricNameLabel, "a"), 1000, 1)
 	require.NoError(t, err)
-	_, err = app.Add(labels.FromStrings(model.MetricNameLabel, "a"), 2000, 1)
+	_, err = app.Append(0, labels.FromStrings(model.MetricNameLabel, "a"), 2000, 1)
 	require.NoError(t, err)
-	_, err = app.Add(labels.FromStrings(model.MetricNameLabel, "a"), 3000, 1)
+	_, err = app.Append(0, labels.FromStrings(model.MetricNameLabel, "a"), 3000, 1)
 	require.NoError(t, err)
 	require.NoError(t, app.Commit())
 
diff --git a/cmd/promtool/backfill.go b/cmd/promtool/backfill.go
index b04fb8b55..c0fc627ee 100644
--- a/cmd/promtool/backfill.go
+++ b/cmd/promtool/backfill.go
@@ -142,7 +142,7 @@ func createBlocks(input []byte, mint, maxt int64, maxSamplesInAppender int, outp
 				l := labels.Labels{}
 				p.Metric(&l)
 
-				if _, err := app.Add(l, *ts, v); err != nil {
+				if _, err := app.Append(0, l, *ts, v); err != nil {
 					return errors.Wrap(err, "add sample")
 				}
 
diff --git a/cmd/promtool/tsdb.go b/cmd/promtool/tsdb.go
index 8d04eadab..c22e12d4b 100644
--- a/cmd/promtool/tsdb.go
+++ b/cmd/promtool/tsdb.go
@@ -35,7 +35,6 @@ import (
 	"github.com/pkg/errors"
 
 	"github.com/prometheus/prometheus/pkg/labels"
-	"github.com/prometheus/prometheus/storage"
 	"github.com/prometheus/prometheus/tsdb"
 	"github.com/prometheus/prometheus/tsdb/chunks"
 	tsdb_errors "github.com/prometheus/prometheus/tsdb/errors"
@@ -206,25 +205,19 @@ func (b *writeBenchmark) ingestScrapesShard(lbls []labels.Labels, scrapeCount in
 		for _, s := range scrape {
 			s.value += 1000
 
-			if s.ref == nil {
-				ref, err := app.Add(s.labels, ts, float64(s.value))
-				if err != nil {
-					panic(err)
-				}
-				s.ref = &ref
-			} else if err := app.AddFast(*s.ref, ts, float64(s.value)); err != nil {
+			var ref uint64
+			if s.ref != nil {
+				ref = *s.ref
+			}
 
-				if errors.Cause(err) != storage.ErrNotFound {
-					panic(err)
-				}
+			ref, err := app.Append(ref, s.labels, ts, float64(s.value))
+			if err != nil {
+				panic(err)
+			}
 
-				ref, err := app.Add(s.labels, ts, float64(s.value))
-				if err != nil {
-					panic(err)
-				}
+			if s.ref == nil {
 				s.ref = &ref
 			}
-
 			total++
 		}
 		if err := app.Commit(); err != nil {
diff --git a/promql/bench_test.go b/promql/bench_test.go
index f1ea31ceb..03111767e 100644
--- a/promql/bench_test.go
+++ b/promql/bench_test.go
@@ -71,10 +71,8 @@ func BenchmarkRangeQuery(b *testing.B) {
 		a := storage.Appender(context.Background())
 		ts := int64(s * 10000) // 10s interval.
 		for i, metric := range metrics {
-			err := a.AddFast(refs[i], ts, float64(s))
-			if err != nil {
-				refs[i], _ = a.Add(metric, ts, float64(s))
-			}
+			ref, _ := a.Append(refs[i], metric, ts, float64(s))
+			refs[i] = ref
 		}
 		if err := a.Commit(); err != nil {
 			b.Fatal(err)
diff --git a/promql/engine_test.go b/promql/engine_test.go
index 6074a48a6..c3a96a9c2 100644
--- a/promql/engine_test.go
+++ b/promql/engine_test.go
@@ -904,14 +904,15 @@ load 1ms
 	// Add some samples with negative timestamp.
 	db := test.TSDB()
 	app := db.Appender(context.Background())
-	ref, err := app.Add(lblsneg, -1000000, 1000)
+	ref, err := app.Append(0, lblsneg, -1000000, 1000)
 	require.NoError(t, err)
 	for ts := int64(-1000000 + 1000); ts <= 0; ts += 1000 {
-		require.NoError(t, app.AddFast(ref, ts, -float64(ts/1000)+1))
+		_, err := app.Append(ref, nil, ts, -float64(ts/1000)+1)
+		require.NoError(t, err)
 	}
 
 	// To test the fix for https://github.com/prometheus/prometheus/issues/8433.
-	_, err = app.Add(labels.FromStrings("__name__", "metric_timestamp"), 3600*1000, 1000)
+	_, err = app.Append(0, labels.FromStrings("__name__", "metric_timestamp"), 3600*1000, 1000)
 	require.NoError(t, err)
 
 	require.NoError(t, app.Commit())
diff --git a/promql/functions_test.go b/promql/functions_test.go
index ffdbd89d3..5707cbed3 100644
--- a/promql/functions_test.go
+++ b/promql/functions_test.go
@@ -43,8 +43,8 @@ func TestDeriv(t *testing.T) {
 	a := storage.Appender(context.Background())
 
 	metric := labels.FromStrings("__name__", "foo")
-	a.Add(metric, 1493712816939, 1.0)
-	a.Add(metric, 1493712846939, 1.0)
+	a.Append(0, metric, 1493712816939, 1.0)
+	a.Append(0, metric, 1493712846939, 1.0)
 
 	require.NoError(t, a.Commit())
 
diff --git a/promql/test.go b/promql/test.go
index 77e133eed..8ee3fc150 100644
--- a/promql/test.go
+++ b/promql/test.go
@@ -307,7 +307,7 @@ func (cmd *loadCmd) append(a storage.Appender) error {
 		m := cmd.metrics[h]
 
 		for _, s := range smpls {
-			if _, err := a.Add(m, s.T, s.V); err != nil {
+			if _, err := a.Append(0, m, s.T, s.V); err != nil {
 				return err
 			}
 		}
@@ -732,7 +732,7 @@ func (ll *LazyLoader) appendTill(ts int64) error {
 				ll.loadCmd.defs[h] = smpls[i:]
 				break
 			}
-			if _, err := app.Add(m, s.T, s.V); err != nil {
+			if _, err := app.Append(0, m, s.T, s.V); err != nil {
 				return err
 			}
 			if i == len(smpls)-1 {
diff --git a/rules/manager.go b/rules/manager.go
index 129d47638..348aa0ce8 100644
--- a/rules/manager.go
+++ b/rules/manager.go
@@ -622,7 +622,7 @@ func (g *Group) Eval(ctx context.Context, ts time.Time) {
 				g.seriesInPreviousEval[i] = seriesReturned
 			}()
 			for _, s := range vector {
-				if _, err := app.Add(s.Metric, s.T, s.V); err != nil {
+				if _, err := app.Append(0, s.Metric, s.T, s.V); err != nil {
 					switch errors.Cause(err) {
 					case storage.ErrOutOfOrderSample:
 						numOutOfOrder++
@@ -647,7 +647,7 @@ func (g *Group) Eval(ctx context.Context, ts time.Time) {
 			for metric, lset := range g.seriesInPreviousEval[i] {
 				if _, ok := seriesReturned[metric]; !ok {
 					// Series no longer exposed, mark it stale.
-					_, err = app.Add(lset, timestamp.FromTime(ts), math.Float64frombits(value.StaleNaN))
+					_, err = app.Append(0, lset, timestamp.FromTime(ts), math.Float64frombits(value.StaleNaN))
 					switch errors.Cause(err) {
 					case nil:
 					case storage.ErrOutOfOrderSample, storage.ErrDuplicateSampleForTimestamp:
@@ -673,7 +673,7 @@ func (g *Group) cleanupStaleSeries(ctx context.Context, ts time.Time) {
 	app := g.opts.Appendable.Appender(ctx)
 	for _, s := range g.staleSeries {
 		// Rule that produced series no longer configured, mark it stale.
-		_, err := app.Add(s, timestamp.FromTime(ts), math.Float64frombits(value.StaleNaN))
+		_, err := app.Append(0, s, timestamp.FromTime(ts), math.Float64frombits(value.StaleNaN))
 		switch errors.Cause(err) {
 		case nil:
 		case storage.ErrOutOfOrderSample, storage.ErrDuplicateSampleForTimestamp:
diff --git a/rules/manager_test.go b/rules/manager_test.go
index 587510d51..3f7810fa8 100644
--- a/rules/manager_test.go
+++ b/rules/manager_test.go
@@ -547,9 +547,9 @@ func TestStaleness(t *testing.T) {
 
 	// A time series that has two samples and then goes stale.
 	app := st.Appender(context.Background())
-	app.Add(labels.FromStrings(model.MetricNameLabel, "a"), 0, 1)
-	app.Add(labels.FromStrings(model.MetricNameLabel, "a"), 1000, 2)
-	app.Add(labels.FromStrings(model.MetricNameLabel, "a"), 2000, math.Float64frombits(value.StaleNaN))
+	app.Append(0, labels.FromStrings(model.MetricNameLabel, "a"), 0, 1)
+	app.Append(0, labels.FromStrings(model.MetricNameLabel, "a"), 1000, 2)
+	app.Append(0, labels.FromStrings(model.MetricNameLabel, "a"), 2000, math.Float64frombits(value.StaleNaN))
 
 	err = app.Commit()
 	require.NoError(t, err)
@@ -872,10 +872,10 @@ func TestNotify(t *testing.T) {
 	})
 
 	app := storage.Appender(context.Background())
-	app.Add(labels.FromStrings(model.MetricNameLabel, "a"), 1000, 2)
-	app.Add(labels.FromStrings(model.MetricNameLabel, "a"), 2000, 3)
-	app.Add(labels.FromStrings(model.MetricNameLabel, "a"), 5000, 3)
-	app.Add(labels.FromStrings(model.MetricNameLabel, "a"), 6000, 0)
+	app.Append(0, labels.FromStrings(model.MetricNameLabel, "a"), 1000, 2)
+	app.Append(0, labels.FromStrings(model.MetricNameLabel, "a"), 2000, 3)
+	app.Append(0, labels.FromStrings(model.MetricNameLabel, "a"), 5000, 3)
+	app.Append(0, labels.FromStrings(model.MetricNameLabel, "a"), 6000, 0)
 
 	err = app.Commit()
 	require.NoError(t, err)
diff --git a/scrape/helpers_test.go b/scrape/helpers_test.go
index b42d144d2..e82b41a61 100644
--- a/scrape/helpers_test.go
+++ b/scrape/helpers_test.go
@@ -28,10 +28,9 @@ func (a nopAppendable) Appender(_ context.Context) storage.Appender {
 
 type nopAppender struct{}
 
-func (a nopAppender) Add(labels.Labels, int64, float64) (uint64, error) { return 0, nil }
-func (a nopAppender) AddFast(uint64, int64, float64) error              { return nil }
-func (a nopAppender) Commit() error                                     { return nil }
-func (a nopAppender) Rollback() error                                   { return nil }
+func (a nopAppender) Append(uint64, labels.Labels, int64, float64) (uint64, error) { return 0, nil }
+func (a nopAppender) Commit() error                                                { return nil }
+func (a nopAppender) Rollback() error                                              { return nil }
 
 type sample struct {
 	metric labels.Labels
@@ -46,47 +45,25 @@ type collectResultAppender struct {
 	result           []sample
 	pendingResult    []sample
 	rolledbackResult []sample
-
-	mapper map[uint64]labels.Labels
 }
 
-func (a *collectResultAppender) AddFast(ref uint64, t int64, v float64) error {
-	if a.next == nil {
-		return storage.ErrNotFound
-	}
-
-	err := a.next.AddFast(ref, t, v)
-	if err != nil {
-		return err
-	}
+func (a *collectResultAppender) Append(ref uint64, lset labels.Labels, t int64, v float64) (uint64, error) {
 	a.pendingResult = append(a.pendingResult, sample{
-		metric: a.mapper[ref],
+		metric: lset,
 		t:      t,
 		v:      v,
 	})
-	return err
-}
 
-func (a *collectResultAppender) Add(m labels.Labels, t int64, v float64) (uint64, error) {
-	a.pendingResult = append(a.pendingResult, sample{
-		metric: m,
-		t:      t,
-		v:      v,
-	})
 	if a.next == nil {
 		return 0, nil
 	}
 
-	if a.mapper == nil {
-		a.mapper = map[uint64]labels.Labels{}
-	}
-
-	ref, err := a.next.Add(m, t, v)
+	ref, err := a.next.Append(ref, lset, t, v)
 	if err != nil {
 		return 0, err
 	}
-	a.mapper[ref] = m
-	return ref, nil
+
+	return ref, err
 }
 
 func (a *collectResultAppender) Commit() error {
diff --git a/scrape/scrape.go b/scrape/scrape.go
index bd89b69f6..bddcdf0d7 100644
--- a/scrape/scrape.go
+++ b/scrape/scrape.go
@@ -1306,20 +1306,19 @@ loop:
 			continue
 		}
 		ce, ok := sl.cache.get(yoloString(met))
+		var (
+			ref  uint64
+			lset labels.Labels
+			mets string
+			hash uint64
+		)
 
 		if ok {
-			err = app.AddFast(ce.ref, t, v)
-			_, err = sl.checkAddError(ce, met, tp, err, &sampleLimitErr, &appErrs)
-			// In theory this should never happen.
-			if err == storage.ErrNotFound {
-				ok = false
-			}
-		}
-		if !ok {
-			var lset labels.Labels
-
-			mets := p.Metric(&lset)
-			hash := lset.Hash()
+			ref = ce.ref
+			lset = ce.lset
+		} else {
+			mets = p.Metric(&lset)
+			hash = lset.Hash()
 
 			// Hash label set as it is seen local to the target. Then add target labels
 			// and relabeling and store the final label set.
@@ -1335,17 +1334,18 @@ loop:
 				err = errNameLabelMandatory
 				break loop
 			}
+		}
 
-			var ref uint64
-			ref, err = app.Add(lset, t, v)
-			sampleAdded, err = sl.checkAddError(nil, met, tp, err, &sampleLimitErr, &appErrs)
-			if err != nil {
-				if err != storage.ErrNotFound {
-					level.Debug(sl.l).Log("msg", "Unexpected error", "series", string(met), "err", err)
-				}
-				break loop
+		ref, err = app.Append(ref, lset, t, v)
+		sampleAdded, err = sl.checkAddError(ce, met, tp, err, &sampleLimitErr, &appErrs)
+		if err != nil {
+			if err != storage.ErrNotFound {
+				level.Debug(sl.l).Log("msg", "Unexpected error", "series", string(met), "err", err)
 			}
+			break loop
+		}
 
+		if !ok {
 			if tp == nil {
 				// Bypass staleness logic if there is an explicit timestamp.
 				sl.cache.trackStaleness(hash, lset)
@@ -1380,7 +1380,7 @@ loop:
 	if err == nil {
 		sl.cache.forEachStale(func(lset labels.Labels) bool {
 			// Series no longer exposed, mark it stale.
-			_, err = app.Add(lset, defTime, math.Float64frombits(value.StaleNaN))
+			_, err = app.Append(0, lset, defTime, math.Float64frombits(value.StaleNaN))
 			switch errors.Cause(err) {
 			case storage.ErrOutOfOrderSample, storage.ErrDuplicateSampleForTimestamp:
 				// Do not count these in logging, as this is expected if a target
@@ -1497,37 +1497,31 @@ func (sl *scrapeLoop) reportStale(app storage.Appender, start time.Time) (err er
 
 func (sl *scrapeLoop) addReportSample(app storage.Appender, s string, t int64, v float64) error {
 	ce, ok := sl.cache.get(s)
+	var ref uint64
+	var lset labels.Labels
 	if ok {
-		err := app.AddFast(ce.ref, t, v)
-		switch errors.Cause(err) {
-		case nil:
-			return nil
-		case storage.ErrNotFound:
-			// Try an Add.
-		case storage.ErrOutOfOrderSample, storage.ErrDuplicateSampleForTimestamp:
-			// Do not log here, as this is expected if a target goes away and comes back
-			// again with a new scrape loop.
-			return nil
-		default:
-			return err
+		ref = ce.ref
+		lset = ce.lset
+	} else {
+		lset = labels.Labels{
+			// The constants are suffixed with the invalid \xff unicode rune to avoid collisions
+			// with scraped metrics in the cache.
+			// We have to drop it when building the actual metric.
+			labels.Label{Name: labels.MetricName, Value: s[:len(s)-1]},
 		}
+		lset = sl.reportSampleMutator(lset)
 	}
-	lset := labels.Labels{
-		// The constants are suffixed with the invalid \xff unicode rune to avoid collisions
-		// with scraped metrics in the cache.
-		// We have to drop it when building the actual metric.
-		labels.Label{Name: labels.MetricName, Value: s[:len(s)-1]},
-	}
-
-	hash := lset.Hash()
-	lset = sl.reportSampleMutator(lset)
 
-	ref, err := app.Add(lset, t, v)
+	ref, err := app.Append(ref, lset, t, v)
 	switch errors.Cause(err) {
 	case nil:
-		sl.cache.addRef(s, ref, lset, hash)
+		if !ok {
+			sl.cache.addRef(s, ref, lset, lset.Hash())
+		}
 		return nil
 	case storage.ErrOutOfOrderSample, storage.ErrDuplicateSampleForTimestamp:
+		// Do not log here, as this is expected if a target goes away and comes back
+		// again with a new scrape loop.
 		return nil
 	default:
 		return err
diff --git a/scrape/scrape_test.go b/scrape/scrape_test.go
index ac972a6e9..928d820da 100644
--- a/scrape/scrape_test.go
+++ b/scrape/scrape_test.go
@@ -1560,7 +1560,7 @@ type errorAppender struct {
 	collectResultAppender
 }
 
-func (app *errorAppender) Add(lset labels.Labels, t int64, v float64) (uint64, error) {
+func (app *errorAppender) Append(ref uint64, lset labels.Labels, t int64, v float64) (uint64, error) {
 	switch lset.Get(model.MetricNameLabel) {
 	case "out_of_order":
 		return 0, storage.ErrOutOfOrderSample
@@ -1569,14 +1569,10 @@ func (app *errorAppender) Add(lset labels.Labels, t int64, v float64) (uint64, e
 	case "out_of_bounds":
 		return 0, storage.ErrOutOfBounds
 	default:
-		return app.collectResultAppender.Add(lset, t, v)
+		return app.collectResultAppender.Append(ref, lset, t, v)
 	}
 }
 
-func (app *errorAppender) AddFast(ref uint64, t int64, v float64) error {
-	return app.collectResultAppender.AddFast(ref, t, v)
-}
-
 func TestScrapeLoopAppendGracefullyIfAmendOrOutOfOrderOrOutOfBounds(t *testing.T) {
 	app := &errorAppender{}
 
diff --git a/scrape/target.go b/scrape/target.go
index 2b4c4301c..f3dd2d0c0 100644
--- a/scrape/target.go
+++ b/scrape/target.go
@@ -290,57 +290,38 @@ type limitAppender struct {
 	i     int
 }
 
-func (app *limitAppender) Add(lset labels.Labels, t int64, v float64) (uint64, error) {
+func (app *limitAppender) Append(ref uint64, lset labels.Labels, t int64, v float64) (uint64, error) {
 	if !value.IsStaleNaN(v) {
 		app.i++
 		if app.i > app.limit {
 			return 0, errSampleLimit
 		}
 	}
-	ref, err := app.Appender.Add(lset, t, v)
+	ref, err := app.Appender.Append(ref, lset, t, v)
 	if err != nil {
 		return 0, err
 	}
 	return ref, nil
 }
 
-func (app *limitAppender) AddFast(ref uint64, t int64, v float64) error {
-	if !value.IsStaleNaN(v) {
-		app.i++
-		if app.i > app.limit {
-			return errSampleLimit
-		}
-	}
-	err := app.Appender.AddFast(ref, t, v)
-	return err
-}
-
 type timeLimitAppender struct {
 	storage.Appender
 
 	maxTime int64
 }
 
-func (app *timeLimitAppender) Add(lset labels.Labels, t int64, v float64) (uint64, error) {
+func (app *timeLimitAppender) Append(ref uint64, lset labels.Labels, t int64, v float64) (uint64, error) {
 	if t > app.maxTime {
 		return 0, storage.ErrOutOfBounds
 	}
 
-	ref, err := app.Appender.Add(lset, t, v)
+	ref, err := app.Appender.Append(ref, lset, t, v)
 	if err != nil {
 		return 0, err
 	}
 	return ref, nil
 }
 
-func (app *timeLimitAppender) AddFast(ref uint64, t int64, v float64) error {
-	if t > app.maxTime {
-		return storage.ErrOutOfBounds
-	}
-	err := app.Appender.AddFast(ref, t, v)
-	return err
-}
-
 // populateLabels builds a label set from the given label set and scrape configuration.
 // It returns a label set before relabeling was applied as the second return value.
 // Returns the original discovered label set found before relabelling was applied if the target is dropped during relabeling.
diff --git a/storage/fanout.go b/storage/fanout.go
index 4bc3db12d..91872b67a 100644
--- a/storage/fanout.go
+++ b/storage/fanout.go
@@ -143,33 +143,20 @@ type fanoutAppender struct {
 	secondaries []Appender
 }
 
-func (f *fanoutAppender) Add(l labels.Labels, t int64, v float64) (uint64, error) {
-	ref, err := f.primary.Add(l, t, v)
+func (f *fanoutAppender) Append(ref uint64, l labels.Labels, t int64, v float64) (uint64, error) {
+	ref, err := f.primary.Append(ref, l, t, v)
 	if err != nil {
 		return ref, err
 	}
 
 	for _, appender := range f.secondaries {
-		if _, err := appender.Add(l, t, v); err != nil {
+		if _, err := appender.Append(ref, l, t, v); err != nil {
 			return 0, err
 		}
 	}
 	return ref, nil
 }
 
-func (f *fanoutAppender) AddFast(ref uint64, t int64, v float64) error {
-	if err := f.primary.AddFast(ref, t, v); err != nil {
-		return err
-	}
-
-	for _, appender := range f.secondaries {
-		if err := appender.AddFast(ref, t, v); err != nil {
-			return err
-		}
-	}
-	return nil
-}
-
 func (f *fanoutAppender) Commit() (err error) {
 	err = f.primary.Commit()
 
diff --git a/storage/fanout_test.go b/storage/fanout_test.go
index cd8877019..486f60f2f 100644
--- a/storage/fanout_test.go
+++ b/storage/fanout_test.go
@@ -36,11 +36,11 @@ func TestFanout_SelectSorted(t *testing.T) {
 	priStorage := teststorage.New(t)
 	defer priStorage.Close()
 	app1 := priStorage.Appender(ctx)
-	app1.Add(inputLabel, 0, 0)
+	app1.Append(0, inputLabel, 0, 0)
 	inputTotalSize++
-	app1.Add(inputLabel, 1000, 1)
+	app1.Append(0, inputLabel, 1000, 1)
 	inputTotalSize++
-	app1.Add(inputLabel, 2000, 2)
+	app1.Append(0, inputLabel, 2000, 2)
 	inputTotalSize++
 	err := app1.Commit()
 	require.NoError(t, err)
@@ -48,11 +48,11 @@ func TestFanout_SelectSorted(t *testing.T) {
 	remoteStorage1 := teststorage.New(t)
 	defer remoteStorage1.Close()
 	app2 := remoteStorage1.Appender(ctx)
-	app2.Add(inputLabel, 3000, 3)
+	app2.Append(0, inputLabel, 3000, 3)
 	inputTotalSize++
-	app2.Add(inputLabel, 4000, 4)
+	app2.Append(0, inputLabel, 4000, 4)
 	inputTotalSize++
-	app2.Add(inputLabel, 5000, 5)
+	app2.Append(0, inputLabel, 5000, 5)
 	inputTotalSize++
 	err = app2.Commit()
 	require.NoError(t, err)
@@ -61,11 +61,11 @@ func TestFanout_SelectSorted(t *testing.T) {
 	defer remoteStorage2.Close()
 
 	app3 := remoteStorage2.Appender(ctx)
-	app3.Add(inputLabel, 6000, 6)
+	app3.Append(0, inputLabel, 6000, 6)
 	inputTotalSize++
-	app3.Add(inputLabel, 7000, 7)
+	app3.Append(0, inputLabel, 7000, 7)
 	inputTotalSize++
-	app3.Add(inputLabel, 8000, 8)
+	app3.Append(0, inputLabel, 8000, 8)
 	inputTotalSize++
 
 	err = app3.Commit()
diff --git a/storage/interface.go b/storage/interface.go
index 711c253a7..eba63b4ce 100644
--- a/storage/interface.go
+++ b/storage/interface.go
@@ -136,18 +136,15 @@ func (f QueryableFunc) Querier(ctx context.Context, mint, maxt int64) (Querier,
 //
 // Operations on the Appender interface are not goroutine-safe.
 type Appender interface {
-	// Add adds a sample pair for the given series. A reference number is
-	// returned which can be used to add further samples in the same or later
-	// transactions.
+	// Append adds a sample pair for the given series.
+	// An optional reference number can be provided to accelerate calls.
+	// A reference number is returned which can be used to add further
+	// samples in the same or later transactions.
 	// Returned reference numbers are ephemeral and may be rejected in calls
-	// to AddFast() at any point. Adding the sample via Add() returns a new
+	// to Append() at any point. Adding the sample via Append() returns a new
 	// reference number.
 	// If the reference is 0 it must not be used for caching.
-	Add(l labels.Labels, t int64, v float64) (uint64, error)
-
-	// AddFast adds a sample pair for the referenced series. It is generally
-	// faster than adding a sample by providing its full label set.
-	AddFast(ref uint64, t int64, v float64) error
+	Append(ref uint64, l labels.Labels, t int64, v float64) (uint64, error)
 
 	// Commit submits the collected samples and purges the batch. If Commit
 	// returns a non-nil error, it also rolls back all modifications made in
diff --git a/storage/remote/write.go b/storage/remote/write.go
index 76c2a650c..c62b143a9 100644
--- a/storage/remote/write.go
+++ b/storage/remote/write.go
@@ -212,8 +212,8 @@ type timestampTracker struct {
 	highestRecvTimestamp *maxTimestamp
 }
 
-// Add implements storage.Appender.
-func (t *timestampTracker) Add(_ labels.Labels, ts int64, _ float64) (uint64, error) {
+// Append implements storage.Appender.
+func (t *timestampTracker) Append(_ uint64, _ labels.Labels, ts int64, _ float64) (uint64, error) {
 	t.samples++
 	if ts > t.highestTimestamp {
 		t.highestTimestamp = ts
@@ -221,12 +221,6 @@ func (t *timestampTracker) Add(_ labels.Labels, ts int64, _ float64) (uint64, er
 	return 0, nil
 }
 
-// AddFast implements storage.Appender.
-func (t *timestampTracker) AddFast(_ uint64, ts int64, v float64) error {
-	_, err := t.Add(nil, ts, v)
-	return err
-}
-
 // Commit implements storage.Appender.
 func (t *timestampTracker) Commit() error {
 	t.writeStorage.samplesIn.incr(t.samples)
diff --git a/storage/remote/write_handler.go b/storage/remote/write_handler.go
index c0538e2b2..435c99607 100644
--- a/storage/remote/write_handler.go
+++ b/storage/remote/write_handler.go
@@ -75,7 +75,7 @@ func (h *handler) write(ctx context.Context, req *prompb.WriteRequest) (err erro
 	for _, ts := range req.Timeseries {
 		labels := labelProtosToLabels(ts.Labels)
 		for _, s := range ts.Samples {
-			_, err = app.Add(labels, s.Timestamp, s.Value)
+			_, err = app.Append(0, labels, s.Timestamp, s.Value)
 			if err != nil {
 				return err
 			}
diff --git a/storage/remote/write_handler_test.go b/storage/remote/write_handler_test.go
index d6d66d0d3..a38ccd63b 100644
--- a/storage/remote/write_handler_test.go
+++ b/storage/remote/write_handler_test.go
@@ -115,7 +115,7 @@ func (m *mockAppendable) Appender(_ context.Context) storage.Appender {
 	return m
 }
 
-func (m *mockAppendable) Add(l labels.Labels, t int64, v float64) (uint64, error) {
+func (m *mockAppendable) Append(_ uint64, l labels.Labels, t int64, v float64) (uint64, error) {
 	if t < m.latest {
 		return 0, storage.ErrOutOfOrderSample
 	}
@@ -129,10 +129,6 @@ func (m *mockAppendable) Commit() error {
 	return m.commitErr
 }
 
-func (*mockAppendable) AddFast(uint64, int64, float64) error {
-	return fmt.Errorf("not implemented")
-}
-
 func (*mockAppendable) Rollback() error {
 	return fmt.Errorf("not implemented")
 }
diff --git a/tsdb/block_test.go b/tsdb/block_test.go
index b3fae03d2..3c2990cf3 100644
--- a/tsdb/block_test.go
+++ b/tsdb/block_test.go
@@ -448,15 +448,10 @@ func createHead(tb testing.TB, w *wal.WAL, series []storage.Series, chunkDir str
 	for _, s := range series {
 		ref := uint64(0)
 		it := s.Iterator()
+		lset := s.Labels()
 		for it.Next() {
 			t, v := it.At()
-			if ref != 0 {
-				err := app.AddFast(ref, t, v)
-				if err == nil {
-					continue
-				}
-			}
-			ref, err = app.Add(s.Labels(), t, v)
+			ref, err = app.Append(ref, lset, t, v)
 			require.NoError(tb, err)
 		}
 		require.NoError(tb, it.Err())
diff --git a/tsdb/blockwriter_test.go b/tsdb/blockwriter_test.go
index 8f1dab73d..2be2d193c 100644
--- a/tsdb/blockwriter_test.go
+++ b/tsdb/blockwriter_test.go
@@ -43,10 +43,10 @@ func TestBlockWriter(t *testing.T) {
 	// Add some series.
 	app := w.Appender(ctx)
 	ts1, v1 := int64(44), float64(7)
-	_, err = app.Add(labels.Labels{{Name: "a", Value: "b"}}, ts1, v1)
+	_, err = app.Append(0, labels.Labels{{Name: "a", Value: "b"}}, ts1, v1)
 	require.NoError(t, err)
 	ts2, v2 := int64(55), float64(12)
-	_, err = app.Add(labels.Labels{{Name: "c", Value: "d"}}, ts2, v2)
+	_, err = app.Append(0, labels.Labels{{Name: "c", Value: "d"}}, ts2, v2)
 	require.NoError(t, err)
 	require.NoError(t, app.Commit())
 	id, err := w.Flush(ctx)
diff --git a/tsdb/compact_test.go b/tsdb/compact_test.go
index 35785f505..a08464216 100644
--- a/tsdb/compact_test.go
+++ b/tsdb/compact_test.go
@@ -1101,7 +1101,7 @@ func BenchmarkCompactionFromHead(b *testing.B) {
 			for ln := 0; ln < labelNames; ln++ {
 				app := h.Appender(context.Background())
 				for lv := 0; lv < labelValues; lv++ {
-					app.Add(labels.FromStrings(fmt.Sprintf("%d", ln), fmt.Sprintf("%d%s%d", lv, postingsBenchSuffix, ln)), 0, 0)
+					app.Append(0, labels.FromStrings(fmt.Sprintf("%d", ln), fmt.Sprintf("%d%s%d", lv, postingsBenchSuffix, ln)), 0, 0)
 				}
 				require.NoError(b, app.Commit())
 			}
@@ -1134,9 +1134,9 @@ func TestDisableAutoCompactions(t *testing.T) {
 	db.DisableCompactions()
 	app := db.Appender(context.Background())
 	for i := int64(0); i < 3; i++ {
-		_, err := app.Add(label, i*blockRange, 0)
+		_, err := app.Append(0, label, i*blockRange, 0)
 		require.NoError(t, err)
-		_, err = app.Add(label, i*blockRange+1000, 0)
+		_, err = app.Append(0, label, i*blockRange+1000, 0)
 		require.NoError(t, err)
 	}
 	require.NoError(t, app.Commit())
@@ -1249,11 +1249,11 @@ func TestDeleteCompactionBlockAfterFailedReload(t *testing.T) {
 
 			// Add some data to the head that is enough to trigger a compaction.
 			app := db.Appender(context.Background())
-			_, err := app.Add(defaultLabel, 1, 0)
+			_, err := app.Append(0, defaultLabel, 1, 0)
 			require.NoError(t, err)
-			_, err = app.Add(defaultLabel, 2, 0)
+			_, err = app.Append(0, defaultLabel, 2, 0)
 			require.NoError(t, err)
-			_, err = app.Add(defaultLabel, 3+rangeToTriggerCompaction, 0)
+			_, err = app.Append(0, defaultLabel, 3+rangeToTriggerCompaction, 0)
 			require.NoError(t, err)
 			require.NoError(t, app.Commit())
 
diff --git a/tsdb/db_test.go b/tsdb/db_test.go
index 6f8fb89bb..4849153de 100644
--- a/tsdb/db_test.go
+++ b/tsdb/db_test.go
@@ -173,7 +173,7 @@ func TestDataAvailableOnlyAfterCommit(t *testing.T) {
 	ctx := context.Background()
 	app := db.Appender(ctx)
 
-	_, err := app.Add(labels.FromStrings("foo", "bar"), 0, 0)
+	_, err := app.Append(0, labels.FromStrings("foo", "bar"), 0, 0)
 	require.NoError(t, err)
 
 	querier, err := db.Querier(context.TODO(), 0, 1)
@@ -206,7 +206,7 @@ func TestNoPanicAfterWALCorruption(t *testing.T) {
 	{
 		for {
 			app := db.Appender(ctx)
-			_, err := app.Add(labels.FromStrings("foo", "bar"), maxt, 0)
+			_, err := app.Append(0, labels.FromStrings("foo", "bar"), maxt, 0)
 			expSamples = append(expSamples, sample{t: maxt, v: 0})
 			require.NoError(t, err)
 			require.NoError(t, app.Commit())
@@ -261,7 +261,7 @@ func TestDataNotAvailableAfterRollback(t *testing.T) {
 	}()
 
 	app := db.Appender(context.Background())
-	_, err := app.Add(labels.FromStrings("foo", "bar"), 0, 0)
+	_, err := app.Append(0, labels.FromStrings("foo", "bar"), 0, 0)
 	require.NoError(t, err)
 
 	err = app.Rollback()
@@ -285,12 +285,13 @@ func TestDBAppenderAddRef(t *testing.T) {
 	ctx := context.Background()
 	app1 := db.Appender(ctx)
 
-	ref1, err := app1.Add(labels.FromStrings("a", "b"), 123, 0)
+	ref1, err := app1.Append(0, labels.FromStrings("a", "b"), 123, 0)
 	require.NoError(t, err)
 
 	// Reference should already work before commit.
-	err = app1.AddFast(ref1, 124, 1)
+	ref2, err := app1.Append(ref1, nil, 124, 1)
 	require.NoError(t, err)
+	require.Equal(t, ref1, ref2)
 
 	err = app1.Commit()
 	require.NoError(t, err)
@@ -298,20 +299,22 @@ func TestDBAppenderAddRef(t *testing.T) {
 	app2 := db.Appender(ctx)
 
 	// first ref should already work in next transaction.
-	err = app2.AddFast(ref1, 125, 0)
+	ref3, err := app2.Append(ref1, nil, 125, 0)
 	require.NoError(t, err)
+	require.Equal(t, ref1, ref3)
 
-	ref2, err := app2.Add(labels.FromStrings("a", "b"), 133, 1)
+	ref4, err := app2.Append(ref1, labels.FromStrings("a", "b"), 133, 1)
 	require.NoError(t, err)
-
-	require.Equal(t, ref1, ref2)
+	require.Equal(t, ref1, ref4)
 
 	// Reference must be valid to add another sample.
-	err = app2.AddFast(ref2, 143, 2)
+	ref5, err := app2.Append(ref2, nil, 143, 2)
 	require.NoError(t, err)
+	require.Equal(t, ref1, ref5)
 
-	err = app2.AddFast(9999999, 1, 1)
-	require.Equal(t, storage.ErrNotFound, errors.Cause(err))
+	// Missing labels & invalid refs should fail.
+	_, err = app2.Append(9999999, nil, 1, 1)
+	require.Equal(t, ErrInvalidSample, errors.Cause(err))
 
 	require.NoError(t, app2.Commit())
 
@@ -340,11 +343,11 @@ func TestAppendEmptyLabelsIgnored(t *testing.T) {
 	ctx := context.Background()
 	app1 := db.Appender(ctx)
 
-	ref1, err := app1.Add(labels.FromStrings("a", "b"), 123, 0)
+	ref1, err := app1.Append(0, labels.FromStrings("a", "b"), 123, 0)
 	require.NoError(t, err)
 
 	// Construct labels manually so there is an empty label.
-	ref2, err := app1.Add(labels.Labels{labels.Label{Name: "a", Value: "b"}, labels.Label{Name: "c", Value: ""}}, 124, 0)
+	ref2, err := app1.Append(0, labels.Labels{labels.Label{Name: "a", Value: "b"}, labels.Label{Name: "c", Value: ""}}, 124, 0)
 	require.NoError(t, err)
 
 	// Should be the same series.
@@ -396,7 +399,7 @@ Outer:
 		smpls := make([]float64, numSamples)
 		for i := int64(0); i < numSamples; i++ {
 			smpls[i] = rand.Float64()
-			app.Add(labels.Labels{{Name: "a", Value: "b"}}, i, smpls[i])
+			app.Append(0, labels.Labels{{Name: "a", Value: "b"}}, i, smpls[i])
 		}
 
 		require.NoError(t, app.Commit())
@@ -452,12 +455,12 @@ func TestAmendDatapointCausesError(t *testing.T) {
 
 	ctx := context.Background()
 	app := db.Appender(ctx)
-	_, err := app.Add(labels.Labels{{Name: "a", Value: "b"}}, 0, 0)
+	_, err := app.Append(0, labels.Labels{{Name: "a", Value: "b"}}, 0, 0)
 	require.NoError(t, err)
 	require.NoError(t, app.Commit())
 
 	app = db.Appender(ctx)
-	_, err = app.Add(labels.Labels{{Name: "a", Value: "b"}}, 0, 1)
+	_, err = app.Append(0, labels.Labels{{Name: "a", Value: "b"}}, 0, 1)
 	require.Equal(t, storage.ErrDuplicateSampleForTimestamp, err)
 	require.NoError(t, app.Rollback())
 }
@@ -470,12 +473,12 @@ func TestDuplicateNaNDatapointNoAmendError(t *testing.T) {
 
 	ctx := context.Background()
 	app := db.Appender(ctx)
-	_, err := app.Add(labels.Labels{{Name: "a", Value: "b"}}, 0, math.NaN())
+	_, err := app.Append(0, labels.Labels{{Name: "a", Value: "b"}}, 0, math.NaN())
 	require.NoError(t, err)
 	require.NoError(t, app.Commit())
 
 	app = db.Appender(ctx)
-	_, err = app.Add(labels.Labels{{Name: "a", Value: "b"}}, 0, math.NaN())
+	_, err = app.Append(0, labels.Labels{{Name: "a", Value: "b"}}, 0, math.NaN())
 	require.NoError(t, err)
 }
 
@@ -487,12 +490,12 @@ func TestNonDuplicateNaNDatapointsCausesAmendError(t *testing.T) {
 
 	ctx := context.Background()
 	app := db.Appender(ctx)
-	_, err := app.Add(labels.Labels{{Name: "a", Value: "b"}}, 0, math.Float64frombits(0x7ff0000000000001))
+	_, err := app.Append(0, labels.Labels{{Name: "a", Value: "b"}}, 0, math.Float64frombits(0x7ff0000000000001))
 	require.NoError(t, err)
 	require.NoError(t, app.Commit())
 
 	app = db.Appender(ctx)
-	_, err = app.Add(labels.Labels{{Name: "a", Value: "b"}}, 0, math.Float64frombits(0x7ff0000000000002))
+	_, err = app.Append(0, labels.Labels{{Name: "a", Value: "b"}}, 0, math.Float64frombits(0x7ff0000000000002))
 	require.Equal(t, storage.ErrDuplicateSampleForTimestamp, err)
 }
 
@@ -504,7 +507,7 @@ func TestEmptyLabelsetCausesError(t *testing.T) {
 
 	ctx := context.Background()
 	app := db.Appender(ctx)
-	_, err := app.Add(labels.Labels{}, 0, 0)
+	_, err := app.Append(0, labels.Labels{}, 0, 0)
 	require.Error(t, err)
 	require.Equal(t, "empty labelset: invalid sample", err.Error())
 }
@@ -518,9 +521,9 @@ func TestSkippingInvalidValuesInSameTxn(t *testing.T) {
 	// Append AmendedValue.
 	ctx := context.Background()
 	app := db.Appender(ctx)
-	_, err := app.Add(labels.Labels{{Name: "a", Value: "b"}}, 0, 1)
+	_, err := app.Append(0, labels.Labels{{Name: "a", Value: "b"}}, 0, 1)
 	require.NoError(t, err)
-	_, err = app.Add(labels.Labels{{Name: "a", Value: "b"}}, 0, 2)
+	_, err = app.Append(0, labels.Labels{{Name: "a", Value: "b"}}, 0, 2)
 	require.NoError(t, err)
 	require.NoError(t, app.Commit())
 
@@ -536,9 +539,9 @@ func TestSkippingInvalidValuesInSameTxn(t *testing.T) {
 
 	// Append Out of Order Value.
 	app = db.Appender(ctx)
-	_, err = app.Add(labels.Labels{{Name: "a", Value: "b"}}, 10, 3)
+	_, err = app.Append(0, labels.Labels{{Name: "a", Value: "b"}}, 10, 3)
 	require.NoError(t, err)
-	_, err = app.Add(labels.Labels{{Name: "a", Value: "b"}}, 7, 5)
+	_, err = app.Append(0, labels.Labels{{Name: "a", Value: "b"}}, 7, 5)
 	require.NoError(t, err)
 	require.NoError(t, app.Commit())
 
@@ -560,7 +563,7 @@ func TestDB_Snapshot(t *testing.T) {
 	app := db.Appender(ctx)
 	mint := int64(1414141414000)
 	for i := 0; i < 1000; i++ {
-		_, err := app.Add(labels.FromStrings("foo", "bar"), mint+int64(i), 1.0)
+		_, err := app.Append(0, labels.FromStrings("foo", "bar"), mint+int64(i), 1.0)
 		require.NoError(t, err)
 	}
 	require.NoError(t, app.Commit())
@@ -610,7 +613,7 @@ func TestDB_Snapshot_ChunksOutsideOfCompactedRange(t *testing.T) {
 	app := db.Appender(ctx)
 	mint := int64(1414141414000)
 	for i := 0; i < 1000; i++ {
-		_, err := app.Add(labels.FromStrings("foo", "bar"), mint+int64(i), 1.0)
+		_, err := app.Append(0, labels.FromStrings("foo", "bar"), mint+int64(i), 1.0)
 		require.NoError(t, err)
 	}
 	require.NoError(t, app.Commit())
@@ -665,7 +668,7 @@ func TestDB_SnapshotWithDelete(t *testing.T) {
 	smpls := make([]float64, numSamples)
 	for i := int64(0); i < numSamples; i++ {
 		smpls[i] = rand.Float64()
-		app.Add(labels.Labels{{Name: "a", Value: "b"}}, i, smpls[i])
+		app.Append(0, labels.Labels{{Name: "a", Value: "b"}}, i, smpls[i])
 	}
 
 	require.NoError(t, app.Commit())
@@ -818,7 +821,7 @@ func TestDB_e2e(t *testing.T) {
 
 			series = append(series, sample{ts, v})
 
-			_, err := app.Add(lset, ts, v)
+			_, err := app.Append(0, lset, ts, v)
 			require.NoError(t, err)
 
 			ts += rand.Int63n(timeInterval) + 1
@@ -912,7 +915,7 @@ func TestWALFlushedOnDBClose(t *testing.T) {
 
 	ctx := context.Background()
 	app := db.Appender(ctx)
-	_, err := app.Add(lbls, 0, 1)
+	_, err := app.Append(0, lbls, 0, 1)
 	require.NoError(t, err)
 	require.NoError(t, app.Commit())
 
@@ -986,10 +989,10 @@ func TestWALSegmentSizeOptions(t *testing.T) {
 
 			for i := int64(0); i < 155; i++ {
 				app := db.Appender(context.Background())
-				ref, err := app.Add(labels.Labels{labels.Label{Name: "wal" + fmt.Sprintf("%d", i), Value: "size"}}, i, rand.Float64())
+				ref, err := app.Append(0, labels.Labels{labels.Label{Name: "wal" + fmt.Sprintf("%d", i), Value: "size"}}, i, rand.Float64())
 				require.NoError(t, err)
 				for j := int64(1); j <= 78; j++ {
-					err := app.AddFast(ref, i+j, rand.Float64())
+					_, err := app.Append(ref, nil, i+j, rand.Float64())
 					require.NoError(t, err)
 				}
 				require.NoError(t, app.Commit())
@@ -1013,7 +1016,7 @@ func TestTombstoneClean(t *testing.T) {
 	smpls := make([]float64, numSamples)
 	for i := int64(0); i < numSamples; i++ {
 		smpls[i] = rand.Float64()
-		app.Add(labels.Labels{{Name: "a", Value: "b"}}, i, smpls[i])
+		app.Append(0, labels.Labels{{Name: "a", Value: "b"}}, i, smpls[i])
 	}
 
 	require.NoError(t, app.Commit())
@@ -1356,7 +1359,7 @@ func TestSizeRetention(t *testing.T) {
 			it := s.Iterator()
 			for it.Next() {
 				tim, v := it.At()
-				_, err := headApp.Add(s.Labels(), tim, v)
+				_, err := headApp.Append(0, s.Labels(), tim, v)
 				require.NoError(t, err)
 			}
 			require.NoError(t, it.Err())
@@ -1472,7 +1475,7 @@ func TestNotMatcherSelectsLabelsUnsetSeries(t *testing.T) {
 	ctx := context.Background()
 	app := db.Appender(ctx)
 	for _, lbls := range labelpairs {
-		_, err := app.Add(lbls, 0, 1)
+		_, err := app.Append(0, lbls, 0, 1)
 		require.NoError(t, err)
 	}
 	require.NoError(t, app.Commit())
@@ -1657,9 +1660,9 @@ func TestChunkAtBlockBoundary(t *testing.T) {
 	label := labels.FromStrings("foo", "bar")
 
 	for i := int64(0); i < 3; i++ {
-		_, err := app.Add(label, i*blockRange, 0)
+		_, err := app.Append(0, label, i*blockRange, 0)
 		require.NoError(t, err)
-		_, err = app.Add(label, i*blockRange+1000, 0)
+		_, err = app.Append(0, label, i*blockRange+1000, 0)
 		require.NoError(t, err)
 	}
 
@@ -1714,9 +1717,9 @@ func TestQuerierWithBoundaryChunks(t *testing.T) {
 	label := labels.FromStrings("foo", "bar")
 
 	for i := int64(0); i < 5; i++ {
-		_, err := app.Add(label, i*blockRange, 0)
+		_, err := app.Append(0, label, i*blockRange, 0)
 		require.NoError(t, err)
-		_, err = app.Add(labels.FromStrings("blockID", strconv.FormatInt(i, 10)), i*blockRange, 0)
+		_, err = app.Append(0, labels.FromStrings("blockID", strconv.FormatInt(i, 10)), i*blockRange, 0)
 		require.NoError(t, err)
 	}
 
@@ -1763,7 +1766,7 @@ func TestInitializeHeadTimestamp(t *testing.T) {
 		// First added sample initializes the writable range.
 		ctx := context.Background()
 		app := db.Appender(ctx)
-		_, err = app.Add(labels.FromStrings("a", "b"), 1000, 1)
+		_, err = app.Append(0, labels.FromStrings("a", "b"), 1000, 1)
 		require.NoError(t, err)
 
 		require.Equal(t, int64(1000), db.head.MinTime())
@@ -1880,11 +1883,11 @@ func TestNoEmptyBlocks(t *testing.T) {
 
 	t.Run("Test no blocks after deleting all samples from head.", func(t *testing.T) {
 		app := db.Appender(ctx)
-		_, err := app.Add(defaultLabel, 1, 0)
+		_, err := app.Append(0, defaultLabel, 1, 0)
 		require.NoError(t, err)
-		_, err = app.Add(defaultLabel, 2, 0)
+		_, err = app.Append(0, defaultLabel, 2, 0)
 		require.NoError(t, err)
-		_, err = app.Add(defaultLabel, 3+rangeToTriggerCompaction, 0)
+		_, err = app.Append(0, defaultLabel, 3+rangeToTriggerCompaction, 0)
 		require.NoError(t, err)
 		require.NoError(t, app.Commit())
 		require.NoError(t, db.Delete(math.MinInt64, math.MaxInt64, defaultMatcher))
@@ -1897,16 +1900,16 @@ func TestNoEmptyBlocks(t *testing.T) {
 		require.Equal(t, 0, len(actBlocks))
 
 		app = db.Appender(ctx)
-		_, err = app.Add(defaultLabel, 1, 0)
+		_, err = app.Append(0, defaultLabel, 1, 0)
 		require.Equal(t, storage.ErrOutOfBounds, err, "the head should be truncated so no samples in the past should be allowed")
 
 		// Adding new blocks.
 		currentTime := db.Head().MaxTime()
-		_, err = app.Add(defaultLabel, currentTime, 0)
+		_, err = app.Append(0, defaultLabel, currentTime, 0)
 		require.NoError(t, err)
-		_, err = app.Add(defaultLabel, currentTime+1, 0)
+		_, err = app.Append(0, defaultLabel, currentTime+1, 0)
 		require.NoError(t, err)
-		_, err = app.Add(defaultLabel, currentTime+rangeToTriggerCompaction, 0)
+		_, err = app.Append(0, defaultLabel, currentTime+rangeToTriggerCompaction, 0)
 		require.NoError(t, err)
 		require.NoError(t, app.Commit())
 
@@ -1923,11 +1926,11 @@ func TestNoEmptyBlocks(t *testing.T) {
 		oldBlocks := db.Blocks()
 		app := db.Appender(ctx)
 		currentTime := db.Head().MaxTime()
-		_, err := app.Add(defaultLabel, currentTime, 0)
+		_, err := app.Append(0, defaultLabel, currentTime, 0)
 		require.NoError(t, err)
-		_, err = app.Add(defaultLabel, currentTime+1, 0)
+		_, err = app.Append(0, defaultLabel, currentTime+1, 0)
 		require.NoError(t, err)
-		_, err = app.Add(defaultLabel, currentTime+rangeToTriggerCompaction, 0)
+		_, err = app.Append(0, defaultLabel, currentTime+rangeToTriggerCompaction, 0)
 		require.NoError(t, err)
 		require.NoError(t, app.Commit())
 		require.NoError(t, db.head.Delete(math.MinInt64, math.MaxInt64, defaultMatcher))
@@ -2009,7 +2012,7 @@ func TestDB_LabelNames(t *testing.T) {
 		for i := mint; i <= maxt; i++ {
 			for _, tuple := range sampleLabels {
 				label := labels.FromStrings(tuple[0], tuple[1])
-				_, err := app.Add(label, i*blockRange, 0)
+				_, err := app.Append(0, label, i*blockRange, 0)
 				require.NoError(t, err)
 			}
 		}
@@ -2076,7 +2079,7 @@ func TestCorrectNumTombstones(t *testing.T) {
 	app := db.Appender(ctx)
 	for i := int64(0); i < 3; i++ {
 		for j := int64(0); j < 15; j++ {
-			_, err := app.Add(defaultLabel, i*blockRange+j, 0)
+			_, err := app.Append(0, defaultLabel, i*blockRange+j, 0)
 			require.NoError(t, err)
 		}
 	}
@@ -2129,16 +2132,16 @@ func TestBlockRanges(t *testing.T) {
 	}()
 	app := db.Appender(ctx)
 	lbl := labels.Labels{{Name: "a", Value: "b"}}
-	_, err = app.Add(lbl, firstBlockMaxT-1, rand.Float64())
+	_, err = app.Append(0, lbl, firstBlockMaxT-1, rand.Float64())
 	if err == nil {
 		t.Fatalf("appending a sample with a timestamp covered by a previous block shouldn't be possible")
 	}
-	_, err = app.Add(lbl, firstBlockMaxT+1, rand.Float64())
+	_, err = app.Append(0, lbl, firstBlockMaxT+1, rand.Float64())
 	require.NoError(t, err)
-	_, err = app.Add(lbl, firstBlockMaxT+2, rand.Float64())
+	_, err = app.Append(0, lbl, firstBlockMaxT+2, rand.Float64())
 	require.NoError(t, err)
 	secondBlockMaxt := firstBlockMaxT + rangeToTriggerCompaction
-	_, err = app.Add(lbl, secondBlockMaxt, rand.Float64()) // Add samples to trigger a new compaction
+	_, err = app.Append(0, lbl, secondBlockMaxt, rand.Float64()) // Add samples to trigger a new compaction
 
 	require.NoError(t, err)
 	require.NoError(t, app.Commit())
@@ -2158,13 +2161,13 @@ func TestBlockRanges(t *testing.T) {
 	// and compaction doesn't create an overlapping block.
 	app = db.Appender(ctx)
 	db.DisableCompactions()
-	_, err = app.Add(lbl, secondBlockMaxt+1, rand.Float64())
+	_, err = app.Append(0, lbl, secondBlockMaxt+1, rand.Float64())
 	require.NoError(t, err)
-	_, err = app.Add(lbl, secondBlockMaxt+2, rand.Float64())
+	_, err = app.Append(0, lbl, secondBlockMaxt+2, rand.Float64())
 	require.NoError(t, err)
-	_, err = app.Add(lbl, secondBlockMaxt+3, rand.Float64())
+	_, err = app.Append(0, lbl, secondBlockMaxt+3, rand.Float64())
 	require.NoError(t, err)
-	_, err = app.Add(lbl, secondBlockMaxt+4, rand.Float64())
+	_, err = app.Append(0, lbl, secondBlockMaxt+4, rand.Float64())
 	require.NoError(t, err)
 	require.NoError(t, app.Commit())
 	require.NoError(t, db.Close())
@@ -2180,7 +2183,7 @@ func TestBlockRanges(t *testing.T) {
 	require.Equal(t, db.Blocks()[2].Meta().MaxTime, thirdBlockMaxt, "unexpected maxt of the last block")
 
 	app = db.Appender(ctx)
-	_, err = app.Add(lbl, thirdBlockMaxt+rangeToTriggerCompaction, rand.Float64()) // Trigger a compaction
+	_, err = app.Append(0, lbl, thirdBlockMaxt+rangeToTriggerCompaction, rand.Float64()) // Trigger a compaction
 	require.NoError(t, err)
 	require.NoError(t, app.Commit())
 	for x := 0; x < 100; x++ {
@@ -2247,7 +2250,7 @@ func TestDBReadOnly(t *testing.T) {
 		dbSizeBeforeAppend, err := fileutil.DirSize(dbWritable.Dir())
 		require.NoError(t, err)
 		app := dbWritable.Appender(context.Background())
-		_, err = app.Add(labels.FromStrings("foo", "bar"), dbWritable.Head().MaxTime()+1, 0)
+		_, err = app.Append(0, labels.FromStrings("foo", "bar"), dbWritable.Head().MaxTime()+1, 0)
 		require.NoError(t, err)
 		require.NoError(t, app.Commit())
 
@@ -2348,7 +2351,7 @@ func TestDBReadOnly_FlushWAL(t *testing.T) {
 		app := db.Appender(ctx)
 		maxt = 1000
 		for i := 0; i < maxt; i++ {
-			_, err := app.Add(labels.FromStrings(defaultLabelName, "flush"), int64(i), 1.0)
+			_, err := app.Append(0, labels.FromStrings(defaultLabelName, "flush"), int64(i), 1.0)
 			require.NoError(t, err)
 		}
 		require.NoError(t, app.Commit())
@@ -2418,7 +2421,7 @@ func TestDBCannotSeePartialCommits(t *testing.T) {
 			app := db.Appender(ctx)
 
 			for j := 0; j < 100; j++ {
-				_, err := app.Add(labels.FromStrings("foo", "bar", "a", strconv.Itoa(j)), int64(iter), float64(iter))
+				_, err := app.Append(0, labels.FromStrings("foo", "bar", "a", strconv.Itoa(j)), int64(iter), float64(iter))
 				require.NoError(t, err)
 			}
 			err = app.Commit()
@@ -2483,7 +2486,7 @@ func TestDBQueryDoesntSeeAppendsAfterCreation(t *testing.T) {
 
 	ctx := context.Background()
 	app := db.Appender(ctx)
-	_, err = app.Add(labels.FromStrings("foo", "bar"), 0, 0)
+	_, err = app.Append(0, labels.FromStrings("foo", "bar"), 0, 0)
 	require.NoError(t, err)
 
 	querierAfterAddButBeforeCommit, err := db.Querier(context.Background(), 0, 1000000)
@@ -2808,7 +2811,7 @@ func TestCompactHead(t *testing.T) {
 	maxt := 100
 	for i := 0; i < maxt; i++ {
 		val := rand.Float64()
-		_, err := app.Add(labels.FromStrings("a", "b"), int64(i), val)
+		_, err := app.Append(0, labels.FromStrings("a", "b"), int64(i), val)
 		require.NoError(t, err)
 		expSamples = append(expSamples, sample{int64(i), val})
 	}
@@ -3008,9 +3011,9 @@ func TestOneCheckpointPerCompactCall(t *testing.T) {
 	// Append samples spanning 59 block ranges.
 	app := db.Appender(context.Background())
 	for i := int64(0); i < 60; i++ {
-		_, err := app.Add(lbls, blockRange*i, rand.Float64())
+		_, err := app.Append(0, lbls, blockRange*i, rand.Float64())
 		require.NoError(t, err)
-		_, err = app.Add(lbls, (blockRange*i)+blockRange/2, rand.Float64())
+		_, err = app.Append(0, lbls, (blockRange*i)+blockRange/2, rand.Float64())
 		require.NoError(t, err)
 		// Rotate the WAL file so that there is >3 files for checkpoint to happen.
 		require.NoError(t, db.head.wal.NextSegment())
@@ -3067,7 +3070,7 @@ func TestOneCheckpointPerCompactCall(t *testing.T) {
 
 	// Adding sample way into the future.
 	app = db.Appender(context.Background())
-	_, err = app.Add(lbls, blockRange*120, rand.Float64())
+	_, err = app.Append(0, lbls, blockRange*120, rand.Float64())
 	require.NoError(t, err)
 	require.NoError(t, app.Commit())
 
diff --git a/tsdb/head.go b/tsdb/head.go
index db40eb89e..31e644da2 100644
--- a/tsdb/head.go
+++ b/tsdb/head.go
@@ -1052,21 +1052,14 @@ type initAppender struct {
 	head *Head
 }
 
-func (a *initAppender) Add(lset labels.Labels, t int64, v float64) (uint64, error) {
+func (a *initAppender) Append(ref uint64, lset labels.Labels, t int64, v float64) (uint64, error) {
 	if a.app != nil {
-		return a.app.Add(lset, t, v)
+		return a.app.Append(ref, lset, t, v)
 	}
+
 	a.head.initTime(t)
 	a.app = a.head.appender()
-
-	return a.app.Add(lset, t, v)
-}
-
-func (a *initAppender) AddFast(ref uint64, t int64, v float64) error {
-	if a.app == nil {
-		return storage.ErrNotFound
-	}
-	return a.app.AddFast(ref, t, v)
+	return a.app.Append(ref, lset, t, v)
 }
 
 func (a *initAppender) Commit() error {
@@ -1178,54 +1171,45 @@ type headAppender struct {
 	closed                          bool
 }
 
-func (a *headAppender) Add(lset labels.Labels, t int64, v float64) (uint64, error) {
+func (a *headAppender) Append(ref uint64, lset labels.Labels, t int64, v float64) (uint64, error) {
 	if t < a.minValidTime {
 		a.head.metrics.outOfBoundSamples.Inc()
 		return 0, storage.ErrOutOfBounds
 	}
 
-	// Ensure no empty labels have gotten through.
-	lset = lset.WithoutEmpty()
-
-	if len(lset) == 0 {
-		return 0, errors.Wrap(ErrInvalidSample, "empty labelset")
-	}
-
-	if l, dup := lset.HasDuplicateLabelNames(); dup {
-		return 0, errors.Wrap(ErrInvalidSample, fmt.Sprintf(`label name "%s" is not unique`, l))
-	}
-
-	s, created, err := a.head.getOrCreate(lset.Hash(), lset)
-	if err != nil {
-		return 0, err
-	}
+	s := a.head.series.getByID(ref)
+	if s == nil {
+		// Ensure no empty labels have gotten through.
+		lset = lset.WithoutEmpty()
+		if len(lset) == 0 {
+			return 0, errors.Wrap(ErrInvalidSample, "empty labelset")
+		}
 
-	if created {
-		a.series = append(a.series, record.RefSeries{
-			Ref:    s.ref,
-			Labels: lset,
-		})
-	}
-	return s.ref, a.AddFast(s.ref, t, v)
-}
+		if l, dup := lset.HasDuplicateLabelNames(); dup {
+			return 0, errors.Wrap(ErrInvalidSample, fmt.Sprintf(`label name "%s" is not unique`, l))
+		}
 
-func (a *headAppender) AddFast(ref uint64, t int64, v float64) error {
-	if t < a.minValidTime {
-		a.head.metrics.outOfBoundSamples.Inc()
-		return storage.ErrOutOfBounds
+		var created bool
+		var err error
+		s, created, err = a.head.getOrCreate(lset.Hash(), lset)
+		if err != nil {
+			return 0, err
+		}
+		if created {
+			a.series = append(a.series, record.RefSeries{
+				Ref:    s.ref,
+				Labels: lset,
+			})
+		}
 	}
 
-	s := a.head.series.getByID(ref)
-	if s == nil {
-		return errors.Wrap(storage.ErrNotFound, "unknown series")
-	}
 	s.Lock()
 	if err := s.appendable(t, v); err != nil {
 		s.Unlock()
 		if err == storage.ErrOutOfOrderSample {
 			a.head.metrics.outOfOrderSamples.Inc()
 		}
-		return err
+		return 0, err
 	}
 	s.pendingCommit = true
 	s.Unlock()
@@ -1238,12 +1222,12 @@ func (a *headAppender) AddFast(ref uint64, t int64, v float64) error {
 	}
 
 	a.samples = append(a.samples, record.RefSample{
-		Ref: ref,
+		Ref: s.ref,
 		T:   t,
 		V:   v,
 	})
 	a.sampleSeries = append(a.sampleSeries, s)
-	return nil
+	return s.ref, nil
 }
 
 func (a *headAppender) log() error {
diff --git a/tsdb/head_test.go b/tsdb/head_test.go
index f534adc59..d47a48790 100644
--- a/tsdb/head_test.go
+++ b/tsdb/head_test.go
@@ -275,14 +275,14 @@ func TestHead_WALMultiRef(t *testing.T) {
 	require.NoError(t, head.Init(0))
 
 	app := head.Appender(context.Background())
-	ref1, err := app.Add(labels.FromStrings("foo", "bar"), 100, 1)
+	ref1, err := app.Append(0, labels.FromStrings("foo", "bar"), 100, 1)
 	require.NoError(t, err)
 	require.NoError(t, app.Commit())
 	require.Equal(t, 1.0, prom_testutil.ToFloat64(head.metrics.chunksCreated))
 
 	// Add another sample outside chunk range to mmap a chunk.
 	app = head.Appender(context.Background())
-	_, err = app.Add(labels.FromStrings("foo", "bar"), 1500, 2)
+	_, err = app.Append(0, labels.FromStrings("foo", "bar"), 1500, 2)
 	require.NoError(t, err)
 	require.NoError(t, app.Commit())
 	require.Equal(t, 2.0, prom_testutil.ToFloat64(head.metrics.chunksCreated))
@@ -290,14 +290,14 @@ func TestHead_WALMultiRef(t *testing.T) {
 	require.NoError(t, head.Truncate(1600))
 
 	app = head.Appender(context.Background())
-	ref2, err := app.Add(labels.FromStrings("foo", "bar"), 1700, 3)
+	ref2, err := app.Append(0, labels.FromStrings("foo", "bar"), 1700, 3)
 	require.NoError(t, err)
 	require.NoError(t, app.Commit())
 	require.Equal(t, 3.0, prom_testutil.ToFloat64(head.metrics.chunksCreated))
 
 	// Add another sample outside chunk range to mmap a chunk.
 	app = head.Appender(context.Background())
-	_, err = app.Add(labels.FromStrings("foo", "bar"), 2000, 4)
+	_, err = app.Append(0, labels.FromStrings("foo", "bar"), 2000, 4)
 	require.NoError(t, err)
 	require.NoError(t, app.Commit())
 	require.Equal(t, 4.0, prom_testutil.ToFloat64(head.metrics.chunksCreated))
@@ -569,7 +569,7 @@ func TestHeadDeleteSimple(t *testing.T) {
 
 				app := head.Appender(context.Background())
 				for _, smpl := range smplsAll {
-					_, err := app.Add(labels.Labels{lblDefault}, smpl.t, smpl.v)
+					_, err := app.Append(0, labels.Labels{lblDefault}, smpl.t, smpl.v)
 					require.NoError(t, err)
 
 				}
@@ -583,7 +583,7 @@ func TestHeadDeleteSimple(t *testing.T) {
 				// Add more samples.
 				app = head.Appender(context.Background())
 				for _, smpl := range c.addSamples {
-					_, err := app.Add(labels.Labels{lblDefault}, smpl.t, smpl.v)
+					_, err := app.Append(0, labels.Labels{lblDefault}, smpl.t, smpl.v)
 					require.NoError(t, err)
 
 				}
@@ -655,7 +655,7 @@ func TestDeleteUntilCurMax(t *testing.T) {
 	smpls := make([]float64, numSamples)
 	for i := int64(0); i < numSamples; i++ {
 		smpls[i] = rand.Float64()
-		_, err := app.Add(labels.Labels{{Name: "a", Value: "b"}}, i, smpls[i])
+		_, err := app.Append(0, labels.Labels{{Name: "a", Value: "b"}}, i, smpls[i])
 		require.NoError(t, err)
 	}
 	require.NoError(t, app.Commit())
@@ -676,7 +676,7 @@ func TestDeleteUntilCurMax(t *testing.T) {
 
 	// Add again and test for presence.
 	app = hb.Appender(context.Background())
-	_, err = app.Add(labels.Labels{{Name: "a", Value: "b"}}, 11, 1)
+	_, err = app.Append(0, labels.Labels{{Name: "a", Value: "b"}}, 11, 1)
 	require.NoError(t, err)
 	require.NoError(t, app.Commit())
 	q, err = NewBlockQuerier(hb, 0, 100000)
@@ -702,7 +702,7 @@ func TestDeletedSamplesAndSeriesStillInWALAfterCheckpoint(t *testing.T) {
 
 	for i := 0; i < numSamples; i++ {
 		app := hb.Appender(context.Background())
-		_, err := app.Add(labels.Labels{{Name: "a", Value: "b"}}, int64(i), 0)
+		_, err := app.Append(0, labels.Labels{{Name: "a", Value: "b"}}, int64(i), 0)
 		require.NoError(t, err)
 		require.NoError(t, app.Commit())
 	}
@@ -800,7 +800,7 @@ func TestDelete_e2e(t *testing.T) {
 		ts := rand.Int63n(300)
 		for i := 0; i < numDatapoints; i++ {
 			v := rand.Float64()
-			_, err := app.Add(ls, ts, v)
+			_, err := app.Append(0, ls, ts, v)
 			require.NoError(t, err)
 			series = append(series, sample{ts, v})
 			ts += rand.Int63n(timeInterval) + 1
@@ -1145,7 +1145,7 @@ func TestUncommittedSamplesNotLostOnTruncate(t *testing.T) {
 
 	app := h.appender()
 	lset := labels.FromStrings("a", "1")
-	_, err := app.Add(lset, 2100, 1)
+	_, err := app.Append(0, lset, 2100, 1)
 	require.NoError(t, err)
 
 	require.NoError(t, h.Truncate(2000))
@@ -1175,7 +1175,7 @@ func TestRemoveSeriesAfterRollbackAndTruncate(t *testing.T) {
 
 	app := h.appender()
 	lset := labels.FromStrings("a", "1")
-	_, err := app.Add(lset, 2100, 1)
+	_, err := app.Append(0, lset, 2100, 1)
 	require.NoError(t, err)
 
 	require.NoError(t, h.Truncate(2000))
@@ -1205,7 +1205,7 @@ func TestHead_LogRollback(t *testing.T) {
 			}()
 
 			app := h.Appender(context.Background())
-			_, err := app.Add(labels.FromStrings("a", "b"), 1, 2)
+			_, err := app.Append(0, labels.FromStrings("a", "b"), 1, 2)
 			require.NoError(t, err)
 
 			require.NoError(t, app.Rollback())
@@ -1397,7 +1397,7 @@ func TestNewWalSegmentOnTruncate(t *testing.T) {
 	}()
 	add := func(ts int64) {
 		app := h.Appender(context.Background())
-		_, err := app.Add(labels.Labels{{Name: "a", Value: "b"}}, ts, 0)
+		_, err := app.Append(0, labels.Labels{{Name: "a", Value: "b"}}, ts, 0)
 		require.NoError(t, err)
 		require.NoError(t, app.Commit())
 	}
@@ -1428,7 +1428,7 @@ func TestAddDuplicateLabelName(t *testing.T) {
 
 	add := func(labels labels.Labels, labelName string) {
 		app := h.Appender(context.Background())
-		_, err := app.Add(labels, 0, 0)
+		_, err := app.Append(0, labels, 0, 0)
 		require.Error(t, err)
 		require.Equal(t, fmt.Sprintf(`label name "%s" is not unique: invalid sample`, labelName), err.Error())
 	}
@@ -1489,7 +1489,7 @@ func TestMemSeriesIsolation(t *testing.T) {
 				app = a
 			}
 
-			_, err := app.Add(labels.FromStrings("foo", "bar"), int64(i), float64(i))
+			_, err := app.Append(0, labels.FromStrings("foo", "bar"), int64(i), float64(i))
 			require.NoError(t, err)
 			require.NoError(t, app.Commit())
 		}
@@ -1517,7 +1517,7 @@ func TestMemSeriesIsolation(t *testing.T) {
 	// Cleanup appendIDs below 500.
 	app := hb.appender()
 	app.cleanupAppendIDsBelow = 500
-	_, err := app.Add(labels.FromStrings("foo", "bar"), int64(i), float64(i))
+	_, err := app.Append(0, labels.FromStrings("foo", "bar"), int64(i), float64(i))
 	require.NoError(t, err)
 	require.NoError(t, app.Commit())
 	i++
@@ -1536,7 +1536,7 @@ func TestMemSeriesIsolation(t *testing.T) {
 	// the only thing with appendIDs.
 	app = hb.appender()
 	app.cleanupAppendIDsBelow = 1000
-	_, err = app.Add(labels.FromStrings("foo", "bar"), int64(i), float64(i))
+	_, err = app.Append(0, labels.FromStrings("foo", "bar"), int64(i), float64(i))
 	require.NoError(t, err)
 	require.NoError(t, app.Commit())
 	require.Equal(t, 999, lastValue(hb, 998))
@@ -1550,7 +1550,7 @@ func TestMemSeriesIsolation(t *testing.T) {
 	// Cleanup appendIDs below 1001, but with a rollback.
 	app = hb.appender()
 	app.cleanupAppendIDsBelow = 1001
-	_, err = app.Add(labels.FromStrings("foo", "bar"), int64(i), float64(i))
+	_, err = app.Append(0, labels.FromStrings("foo", "bar"), int64(i), float64(i))
 	require.NoError(t, err)
 	require.NoError(t, app.Rollback())
 	require.Equal(t, 1000, lastValue(hb, 999))
@@ -1586,7 +1586,7 @@ func TestMemSeriesIsolation(t *testing.T) {
 	// Cleanup appendIDs below 1000, which means the sample buffer is
 	// the only thing with appendIDs.
 	app = hb.appender()
-	_, err = app.Add(labels.FromStrings("foo", "bar"), int64(i), float64(i))
+	_, err = app.Append(0, labels.FromStrings("foo", "bar"), int64(i), float64(i))
 	i++
 	require.NoError(t, err)
 	require.NoError(t, app.Commit())
@@ -1599,7 +1599,7 @@ func TestMemSeriesIsolation(t *testing.T) {
 
 	// Cleanup appendIDs below 1002, but with a rollback.
 	app = hb.appender()
-	_, err = app.Add(labels.FromStrings("foo", "bar"), int64(i), float64(i))
+	_, err = app.Append(0, labels.FromStrings("foo", "bar"), int64(i), float64(i))
 	require.NoError(t, err)
 	require.NoError(t, app.Rollback())
 	require.Equal(t, 1001, lastValue(hb, 999))
@@ -1617,21 +1617,21 @@ func TestIsolationRollback(t *testing.T) {
 	}()
 
 	app := hb.Appender(context.Background())
-	_, err := app.Add(labels.FromStrings("foo", "bar"), 0, 0)
+	_, err := app.Append(0, labels.FromStrings("foo", "bar"), 0, 0)
 	require.NoError(t, err)
 	require.NoError(t, app.Commit())
 	require.Equal(t, uint64(1), hb.iso.lowWatermark())
 
 	app = hb.Appender(context.Background())
-	_, err = app.Add(labels.FromStrings("foo", "bar"), 1, 1)
+	_, err = app.Append(0, labels.FromStrings("foo", "bar"), 1, 1)
 	require.NoError(t, err)
-	_, err = app.Add(labels.FromStrings("foo", "bar", "foo", "baz"), 2, 2)
+	_, err = app.Append(0, labels.FromStrings("foo", "bar", "foo", "baz"), 2, 2)
 	require.Error(t, err)
 	require.NoError(t, app.Rollback())
 	require.Equal(t, uint64(2), hb.iso.lowWatermark())
 
 	app = hb.Appender(context.Background())
-	_, err = app.Add(labels.FromStrings("foo", "bar"), 3, 3)
+	_, err = app.Append(0, labels.FromStrings("foo", "bar"), 3, 3)
 	require.NoError(t, err)
 	require.NoError(t, app.Commit())
 	require.Equal(t, uint64(3), hb.iso.lowWatermark(), "Low watermark should proceed to 3 even if append #2 was rolled back.")
@@ -1644,18 +1644,18 @@ func TestIsolationLowWatermarkMonotonous(t *testing.T) {
 	}()
 
 	app1 := hb.Appender(context.Background())
-	_, err := app1.Add(labels.FromStrings("foo", "bar"), 0, 0)
+	_, err := app1.Append(0, labels.FromStrings("foo", "bar"), 0, 0)
 	require.NoError(t, err)
 	require.NoError(t, app1.Commit())
 	require.Equal(t, uint64(1), hb.iso.lowWatermark(), "Low watermark should by 1 after 1st append.")
 
 	app1 = hb.Appender(context.Background())
-	_, err = app1.Add(labels.FromStrings("foo", "bar"), 1, 1)
+	_, err = app1.Append(0, labels.FromStrings("foo", "bar"), 1, 1)
 	require.NoError(t, err)
 	require.Equal(t, uint64(2), hb.iso.lowWatermark(), "Low watermark should be two, even if append is not committed yet.")
 
 	app2 := hb.Appender(context.Background())
-	_, err = app2.Add(labels.FromStrings("foo", "baz"), 1, 1)
+	_, err = app2.Append(0, labels.FromStrings("foo", "baz"), 1, 1)
 	require.NoError(t, err)
 	require.NoError(t, app2.Commit())
 	require.Equal(t, uint64(2), hb.iso.lowWatermark(), "Low watermark should stay two because app1 is not committed yet.")
@@ -1701,7 +1701,7 @@ func TestIsolationWithoutAdd(t *testing.T) {
 	require.NoError(t, app.Commit())
 
 	app = hb.Appender(context.Background())
-	_, err := app.Add(labels.FromStrings("foo", "baz"), 1, 1)
+	_, err := app.Append(0, labels.FromStrings("foo", "baz"), 1, 1)
 	require.NoError(t, err)
 	require.NoError(t, app.Commit())
 
@@ -1725,7 +1725,7 @@ func TestOutOfOrderSamplesMetric(t *testing.T) {
 	ctx := context.Background()
 	app := db.Appender(ctx)
 	for i := 1; i <= 5; i++ {
-		_, err = app.Add(labels.FromStrings("a", "b"), int64(i), 99)
+		_, err = app.Append(0, labels.FromStrings("a", "b"), int64(i), 99)
 		require.NoError(t, err)
 	}
 	require.NoError(t, app.Commit())
@@ -1733,22 +1733,22 @@ func TestOutOfOrderSamplesMetric(t *testing.T) {
 	// Test out of order metric.
 	require.Equal(t, 0.0, prom_testutil.ToFloat64(db.head.metrics.outOfOrderSamples))
 	app = db.Appender(ctx)
-	_, err = app.Add(labels.FromStrings("a", "b"), 2, 99)
+	_, err = app.Append(0, labels.FromStrings("a", "b"), 2, 99)
 	require.Equal(t, storage.ErrOutOfOrderSample, err)
 	require.Equal(t, 1.0, prom_testutil.ToFloat64(db.head.metrics.outOfOrderSamples))
 
-	_, err = app.Add(labels.FromStrings("a", "b"), 3, 99)
+	_, err = app.Append(0, labels.FromStrings("a", "b"), 3, 99)
 	require.Equal(t, storage.ErrOutOfOrderSample, err)
 	require.Equal(t, 2.0, prom_testutil.ToFloat64(db.head.metrics.outOfOrderSamples))
 
-	_, err = app.Add(labels.FromStrings("a", "b"), 4, 99)
+	_, err = app.Append(0, labels.FromStrings("a", "b"), 4, 99)
 	require.Equal(t, storage.ErrOutOfOrderSample, err)
 	require.Equal(t, 3.0, prom_testutil.ToFloat64(db.head.metrics.outOfOrderSamples))
 	require.NoError(t, app.Commit())
 
 	// Compact Head to test out of bound metric.
 	app = db.Appender(ctx)
-	_, err = app.Add(labels.FromStrings("a", "b"), DefaultBlockDuration*2, 99)
+	_, err = app.Append(0, labels.FromStrings("a", "b"), DefaultBlockDuration*2, 99)
 	require.NoError(t, err)
 	require.NoError(t, app.Commit())
 
@@ -1757,11 +1757,11 @@ func TestOutOfOrderSamplesMetric(t *testing.T) {
 	require.Greater(t, db.head.minValidTime.Load(), int64(0))
 
 	app = db.Appender(ctx)
-	_, err = app.Add(labels.FromStrings("a", "b"), db.head.minValidTime.Load()-2, 99)
+	_, err = app.Append(0, labels.FromStrings("a", "b"), db.head.minValidTime.Load()-2, 99)
 	require.Equal(t, storage.ErrOutOfBounds, err)
 	require.Equal(t, 1.0, prom_testutil.ToFloat64(db.head.metrics.outOfBoundSamples))
 
-	_, err = app.Add(labels.FromStrings("a", "b"), db.head.minValidTime.Load()-1, 99)
+	_, err = app.Append(0, labels.FromStrings("a", "b"), db.head.minValidTime.Load()-1, 99)
 	require.Equal(t, storage.ErrOutOfBounds, err)
 	require.Equal(t, 2.0, prom_testutil.ToFloat64(db.head.metrics.outOfBoundSamples))
 	require.NoError(t, app.Commit())
@@ -1769,22 +1769,22 @@ func TestOutOfOrderSamplesMetric(t *testing.T) {
 	// Some more valid samples for out of order.
 	app = db.Appender(ctx)
 	for i := 1; i <= 5; i++ {
-		_, err = app.Add(labels.FromStrings("a", "b"), db.head.minValidTime.Load()+DefaultBlockDuration+int64(i), 99)
+		_, err = app.Append(0, labels.FromStrings("a", "b"), db.head.minValidTime.Load()+DefaultBlockDuration+int64(i), 99)
 		require.NoError(t, err)
 	}
 	require.NoError(t, app.Commit())
 
 	// Test out of order metric.
 	app = db.Appender(ctx)
-	_, err = app.Add(labels.FromStrings("a", "b"), db.head.minValidTime.Load()+DefaultBlockDuration+2, 99)
+	_, err = app.Append(0, labels.FromStrings("a", "b"), db.head.minValidTime.Load()+DefaultBlockDuration+2, 99)
 	require.Equal(t, storage.ErrOutOfOrderSample, err)
 	require.Equal(t, 4.0, prom_testutil.ToFloat64(db.head.metrics.outOfOrderSamples))
 
-	_, err = app.Add(labels.FromStrings("a", "b"), db.head.minValidTime.Load()+DefaultBlockDuration+3, 99)
+	_, err = app.Append(0, labels.FromStrings("a", "b"), db.head.minValidTime.Load()+DefaultBlockDuration+3, 99)
 	require.Equal(t, storage.ErrOutOfOrderSample, err)
 	require.Equal(t, 5.0, prom_testutil.ToFloat64(db.head.metrics.outOfOrderSamples))
 
-	_, err = app.Add(labels.FromStrings("a", "b"), db.head.minValidTime.Load()+DefaultBlockDuration+4, 99)
+	_, err = app.Append(0, labels.FromStrings("a", "b"), db.head.minValidTime.Load()+DefaultBlockDuration+4, 99)
 	require.Equal(t, storage.ErrOutOfOrderSample, err)
 	require.Equal(t, 6.0, prom_testutil.ToFloat64(db.head.metrics.outOfOrderSamples))
 	require.NoError(t, app.Commit())
@@ -1798,10 +1798,10 @@ func testHeadSeriesChunkRace(t *testing.T) {
 	require.NoError(t, h.Init(0))
 	app := h.Appender(context.Background())
 
-	s2, err := app.Add(labels.FromStrings("foo2", "bar"), 5, 0)
+	s2, err := app.Append(0, labels.FromStrings("foo2", "bar"), 5, 0)
 	require.NoError(t, err)
 	for ts := int64(6); ts < 11; ts++ {
-		err = app.AddFast(s2, ts, 0)
+		_, err = app.Append(s2, nil, ts, 0)
 		require.NoError(t, err)
 	}
 	require.NoError(t, app.Commit())
@@ -1847,7 +1847,7 @@ func TestHeadLabelNamesValuesWithMinMaxRange(t *testing.T) {
 
 	app := head.Appender(context.Background())
 	for i, name := range expectedLabelNames {
-		_, err := app.Add(labels.Labels{{Name: name, Value: expectedLabelValues[i]}}, seriesTimestamps[i], 0)
+		_, err := app.Append(0, labels.Labels{{Name: name, Value: expectedLabelValues[i]}}, seriesTimestamps[i], 0)
 		require.NoError(t, err)
 	}
 	require.NoError(t, app.Commit())
@@ -1892,7 +1892,7 @@ func TestHeadLabelValuesWithMatchers(t *testing.T) {
 
 	app := head.Appender(context.Background())
 	for i := 0; i < 100; i++ {
-		_, err := app.Add(labels.Labels{
+		_, err := app.Append(0, labels.Labels{
 			{Name: "unique", Value: fmt.Sprintf("value%d", i)},
 			{Name: "tens", Value: fmt.Sprintf("value%d", i/10)},
 		}, 100, 0)
@@ -1952,28 +1952,28 @@ func TestErrReuseAppender(t *testing.T) {
 	}()
 
 	app := head.Appender(context.Background())
-	_, err := app.Add(labels.Labels{{Name: "test", Value: "test"}}, 0, 0)
+	_, err := app.Append(0, labels.Labels{{Name: "test", Value: "test"}}, 0, 0)
 	require.NoError(t, err)
 	require.NoError(t, app.Commit())
 	require.Error(t, app.Commit())
 	require.Error(t, app.Rollback())
 
 	app = head.Appender(context.Background())
-	_, err = app.Add(labels.Labels{{Name: "test", Value: "test"}}, 1, 0)
+	_, err = app.Append(0, labels.Labels{{Name: "test", Value: "test"}}, 1, 0)
 	require.NoError(t, err)
 	require.NoError(t, app.Rollback())
 	require.Error(t, app.Rollback())
 	require.Error(t, app.Commit())
 
 	app = head.Appender(context.Background())
-	_, err = app.Add(labels.Labels{{Name: "test", Value: "test"}}, 2, 0)
+	_, err = app.Append(0, labels.Labels{{Name: "test", Value: "test"}}, 2, 0)
 	require.NoError(t, err)
 	require.NoError(t, app.Commit())
 	require.Error(t, app.Rollback())
 	require.Error(t, app.Commit())
 
 	app = head.Appender(context.Background())
-	_, err = app.Add(labels.Labels{{Name: "test", Value: "test"}}, 3, 0)
+	_, err = app.Append(0, labels.Labels{{Name: "test", Value: "test"}}, 3, 0)
 	require.NoError(t, err)
 	require.NoError(t, app.Rollback())
 	require.Error(t, app.Commit())
@@ -1985,11 +1985,11 @@ func TestHeadMintAfterTruncation(t *testing.T) {
 	head, _ := newTestHead(t, chunkRange, false)
 
 	app := head.Appender(context.Background())
-	_, err := app.Add(labels.Labels{{Name: "a", Value: "b"}}, 100, 100)
+	_, err := app.Append(0, labels.Labels{{Name: "a", Value: "b"}}, 100, 100)
 	require.NoError(t, err)
-	_, err = app.Add(labels.Labels{{Name: "a", Value: "b"}}, 4000, 200)
+	_, err = app.Append(0, labels.Labels{{Name: "a", Value: "b"}}, 4000, 200)
 	require.NoError(t, err)
-	_, err = app.Add(labels.Labels{{Name: "a", Value: "b"}}, 8000, 300)
+	_, err = app.Append(0, labels.Labels{{Name: "a", Value: "b"}}, 8000, 300)
 	require.NoError(t, err)
 	require.NoError(t, app.Commit())
 
@@ -2023,7 +2023,7 @@ func BenchmarkHeadLabelValuesWithMatchers(b *testing.B) {
 
 	metricCount := 1000000
 	for i := 0; i < metricCount; i++ {
-		_, err := app.Add(labels.Labels{
+		_, err := app.Append(0, labels.Labels{
 			{Name: "unique", Value: fmt.Sprintf("value%d", i)},
 			{Name: "tens", Value: fmt.Sprintf("value%d", i/(metricCount/10))},
 			{Name: "ninety", Value: fmt.Sprintf("value%d", i/(metricCount/10)/9)}, // "0" for the first 90%, then "1"
diff --git a/tsdb/querier_bench_test.go b/tsdb/querier_bench_test.go
index 6002c6c7a..a04b1d3e4 100644
--- a/tsdb/querier_bench_test.go
+++ b/tsdb/querier_bench_test.go
@@ -48,7 +48,7 @@ func BenchmarkPostingsForMatchers(b *testing.B) {
 
 	app := h.Appender(context.Background())
 	addSeries := func(l labels.Labels) {
-		app.Add(l, 0, 0)
+		app.Append(0, l, 0, 0)
 	}
 
 	for n := 0; n < 10; n++ {
@@ -158,7 +158,7 @@ func BenchmarkQuerierSelect(b *testing.B) {
 	app := h.Appender(context.Background())
 	numSeries := 1000000
 	for i := 0; i < numSeries; i++ {
-		app.Add(labels.FromStrings("foo", "bar", "i", fmt.Sprintf("%d%s", i, postingsBenchSuffix)), int64(i), 0)
+		app.Append(0, labels.FromStrings("foo", "bar", "i", fmt.Sprintf("%d%s", i, postingsBenchSuffix)), int64(i), 0)
 	}
 	require.NoError(b, app.Commit())
 
diff --git a/tsdb/querier_test.go b/tsdb/querier_test.go
index f5697201b..67346694d 100644
--- a/tsdb/querier_test.go
+++ b/tsdb/querier_test.go
@@ -417,7 +417,7 @@ func TestBlockQuerier_AgainstHeadWithOpenChunks(t *testing.T) {
 			for _, s := range testData {
 				for _, chk := range s.chunks {
 					for _, sample := range chk {
-						_, err = app.Add(labels.FromMap(s.lset), sample.t, sample.v)
+						_, err = app.Append(0, labels.FromMap(s.lset), sample.t, sample.v)
 						require.NoError(t, err)
 					}
 				}
@@ -1579,11 +1579,11 @@ func TestPostingsForMatchers(t *testing.T) {
 	}()
 
 	app := h.Appender(context.Background())
-	app.Add(labels.FromStrings("n", "1"), 0, 0)
-	app.Add(labels.FromStrings("n", "1", "i", "a"), 0, 0)
-	app.Add(labels.FromStrings("n", "1", "i", "b"), 0, 0)
-	app.Add(labels.FromStrings("n", "2"), 0, 0)
-	app.Add(labels.FromStrings("n", "2.5"), 0, 0)
+	app.Append(0, labels.FromStrings("n", "1"), 0, 0)
+	app.Append(0, labels.FromStrings("n", "1", "i", "a"), 0, 0)
+	app.Append(0, labels.FromStrings("n", "1", "i", "b"), 0, 0)
+	app.Append(0, labels.FromStrings("n", "2"), 0, 0)
+	app.Append(0, labels.FromStrings("n", "2.5"), 0, 0)
 	require.NoError(t, app.Commit())
 
 	cases := []struct {
diff --git a/tsdb/tsdbblockutil.go b/tsdb/tsdbblockutil.go
index be2c63f9f..8cc0dd195 100644
--- a/tsdb/tsdbblockutil.go
+++ b/tsdb/tsdbblockutil.go
@@ -50,14 +50,10 @@ func CreateBlock(series []storage.Series, dir string, chunkRange int64, logger l
 	for _, s := range series {
 		ref := uint64(0)
 		it := s.Iterator()
+		lset := s.Labels()
 		for it.Next() {
 			t, v := it.At()
-			if ref != 0 {
-				if err := app.AddFast(ref, t, v); err == nil {
-					continue
-				}
-			}
-			ref, err = app.Add(s.Labels(), t, v)
+			ref, err = app.Append(ref, lset, t, v)
 			if err != nil {
 				return "", err
 			}