diff --git a/db.go b/db.go
index 175ad0c52..2add43a5d 100644
--- a/db.go
+++ b/db.go
@@ -323,6 +323,35 @@ func (db *DB) Close() error {
 	return merr.Err()
 }
 
+func (db *DB) Appender() Appender {
+	return &dbAppender{db: db}
+}
+
+type dbAppender struct {
+	db  *DB
+	buf []hashedSample
+}
+
+func (a *dbAppender) Add(lset labels.Labels, t int64, v float64) error {
+	return a.add(hashedSample{
+		hash:   lset.Hash(),
+		labels: lset,
+		t:      t,
+		v:      v,
+	})
+}
+
+func (a *dbAppender) add(s hashedSample) error {
+	a.buf = append(a.buf, s)
+	return nil
+}
+
+func (a *dbAppender) Commit() error {
+	err := a.db.appendBatch(a.buf)
+	a.buf = a.buf[:0]
+	return err
+}
+
 func (db *DB) appendBatch(samples []hashedSample) error {
 	if len(samples) == 0 {
 		return nil
@@ -335,9 +364,9 @@ func (db *DB) appendBatch(samples []hashedSample) error {
 	// TODO(fabxc): distinguish samples between concurrent heads for
 	// different time blocks. Those may occurr during transition to still
 	// allow late samples to arrive for a previous block.
-	err := head.appendBatch(samples)
+	n, err := head.appendBatch(samples)
 	if err == nil {
-		db.metrics.samplesAppended.Add(float64(len(samples)))
+		db.metrics.samplesAppended.Add(float64(n))
 	}
 
 	if head.fullness() > 1.0 {
@@ -583,45 +612,42 @@ func (db *PartitionedDB) Close() error {
 
 // Appender returns a new appender against the database.
 func (db *PartitionedDB) Appender() Appender {
-	return &partitionedAppender{
-		db:      db,
-		buckets: make([][]hashedSample, len(db.Partitions)),
+	app := &partitionedAppender{db: db}
+
+	for _, p := range db.Partitions {
+		app.buckets = append(app.buckets, p.Appender().(*dbAppender))
 	}
+	return app
 }
 
 type partitionedAppender struct {
 	db      *PartitionedDB
-	buckets [][]hashedSample
+	buckets []*dbAppender
 }
 
-func (ba *partitionedAppender) Add(lset labels.Labels, t int64, v float64) error {
-	h := lset.Hash()
-	s := h >> (64 - ba.db.partitionPow)
+func (ba *partitionedAppender) SetSeries(lset labels.Labels) (uint32, error) {
 
-	ba.buckets[s] = append(ba.buckets[s], hashedSample{
+	return 0, nil
+}
+
+func (a *partitionedAppender) Add(lset labels.Labels, t int64, v float64) error {
+	h := lset.Hash()
+	s := h >> (64 - a.db.partitionPow)
+
+	return a.buckets[s].add(hashedSample{
 		hash:   h,
 		labels: lset,
 		t:      t,
 		v:      v,
 	})
-
-	return nil
-}
-
-func (ba *partitionedAppender) reset() {
-	for i := range ba.buckets {
-		ba.buckets[i] = ba.buckets[i][:0]
-	}
 }
 
 func (ba *partitionedAppender) Commit() error {
-	defer ba.reset()
-
 	var merr MultiError
 
 	// Spill buckets into partitiondb.
-	for s, b := range ba.buckets {
-		merr.Add(ba.db.Partitions[s].appendBatch(b))
+	for _, b := range ba.buckets {
+		merr.Add(b.Commit())
 	}
 	return merr.Err()
 }
diff --git a/head.go b/head.go
index 5eafb4f95..4c1de4000 100644
--- a/head.go
+++ b/head.go
@@ -284,7 +284,7 @@ var (
 	ErrAmendSample = errors.New("amending sample")
 )
 
-func (h *HeadBlock) appendBatch(samples []hashedSample) error {
+func (h *HeadBlock) appendBatch(samples []hashedSample) (int, error) {
 	// Find head chunks for all samples and allocate new IDs/refs for
 	// ones we haven't seen before.
 	var (
@@ -303,10 +303,10 @@ func (h *HeadBlock) appendBatch(samples []hashedSample) error {
 		if cd != nil {
 			// Samples must only occur in order.
 			if s.t < cd.lastTimestamp {
-				return ErrOutOfOrderSample
+				return 0, ErrOutOfOrderSample
 			}
 			if cd.lastTimestamp == s.t && cd.lastValue != s.v {
-				return ErrAmendSample
+				return 0, ErrAmendSample
 			}
 			// TODO(fabxc): sample refs are only scoped within a block for
 			// now and we ignore any previously set value
@@ -332,7 +332,7 @@ func (h *HeadBlock) appendBatch(samples []hashedSample) error {
 	// Write all new series and samples to the WAL and add it to the
 	// in-mem database on success.
 	if err := h.wal.Log(newSeries, samples); err != nil {
-		return err
+		return 0, err
 	}
 
 	// After the samples were successfully written to the WAL, there may
@@ -392,7 +392,7 @@ func (h *HeadBlock) appendBatch(samples []hashedSample) error {
 		h.bstats.MaxTime = maxt
 	}
 
-	return nil
+	return int(total), nil
 }
 
 func (h *HeadBlock) fullness() float64 {