diff --git a/api.go b/api.go
index 045a4fa..b9403ee 100644
--- a/api.go
+++ b/api.go
@@ -3,6 +3,7 @@ package main
 import (
 	"context"
 	"encoding/json"
+	"fmt"
 	"log"
 	"net/http"
 	"strconv"
@@ -143,11 +144,55 @@ func handleStats(rw http.ResponseWriter, r *http.Request) {
 	}
 }
 
+func handleFree(rw http.ResponseWriter, r *http.Request) {
+	vars := mux.Vars(r)
+	to, err := strconv.ParseInt(vars["to"], 10, 64)
+	if err != nil {
+		http.Error(rw, err.Error(), http.StatusBadRequest)
+		return
+	}
+
+	// TODO: lastCheckpoint might be modified by different go-routines.
+	// Load it using the sync/atomic package?
+	freeUpTo := lastCheckpoint.Unix()
+	if to < freeUpTo {
+		freeUpTo = to
+	}
+
+	if r.Method != http.MethodPost {
+		http.Error(rw, "Method Not Allowed", http.StatusMethodNotAllowed)
+		return
+	}
+
+	bodyDec := json.NewDecoder(r.Body)
+	var selectors [][]string
+	err = bodyDec.Decode(&selectors)
+	if err != nil {
+		http.Error(rw, err.Error(), http.StatusBadRequest)
+		return
+	}
+
+	n := 0
+	for _, sel := range selectors {
+		bn, err := memoryStore.Free(sel, freeUpTo)
+		if err != nil {
+			http.Error(rw, err.Error(), http.StatusInternalServerError)
+			return
+		}
+
+		n += bn
+	}
+
+	rw.WriteHeader(http.StatusOK)
+	rw.Write([]byte(fmt.Sprintf("buffers freed: %d\n", n)))
+}
+
 func StartApiServer(address string, done chan bool) error {
 	r := mux.NewRouter()
 
 	r.HandleFunc("/api/{from:[0-9]+}/{to:[0-9]+}/timeseries", handleTimeseries)
 	r.HandleFunc("/api/{from:[0-9]+}/{to:[0-9]+}/stats", handleStats)
+	r.HandleFunc("/api/{to:[0-9]+}/free", handleFree)
 
 	server := &http.Server{
 		Handler:      r,
diff --git a/archive.go b/archive.go
index 6a18f8d..22ae86a 100644
--- a/archive.go
+++ b/archive.go
@@ -65,11 +65,16 @@ func (l *level) toArchiveFile(from, to int64) (*ArchiveFile, error) {
 	}
 
 	for metric, b := range l.metrics {
-		data, start, _, err := b.read(from, to)
+		data := make([]Float, (to-from)/b.frequency)
+		data, start, end, err := b.read(from, to, data)
 		if err != nil {
 			return nil, err
 		}
 
+		for i := int((end - start) / b.frequency); i < len(data); i++ {
+			data[i] = NaN
+		}
+
 		retval.Metrics[metric] = &ArchiveMetrics{
 			Frequency: b.frequency,
 			Start:     start,
diff --git a/stats.go b/stats.go
index 1d2b10b..e47f74d 100644
--- a/stats.go
+++ b/stats.go
@@ -13,7 +13,7 @@ type Stats struct {
 }
 
 // Return `Stats` by value for less allocations/GC?
-func (b *buffer) stats(from, to int64) (*Stats, int64, int64, error) {
+func (b *buffer) stats(from, to int64) (Stats, int64, int64, error) {
 	if from < b.start {
 		if b.prev != nil {
 			return b.prev.stats(from, to)
@@ -50,7 +50,7 @@ func (b *buffer) stats(from, to int64) (*Stats, int64, int64, error) {
 		max = math.Max(max, xf)
 	}
 
-	return &Stats{
+	return Stats{
 		Samples: samples,
 		Avg:     Float(sum) / Float(samples),
 		Min:     Float(min),
@@ -61,59 +61,56 @@ func (b *buffer) stats(from, to int64) (*Stats, int64, int64, error) {
 // This function assmumes that `l.lock` is LOCKED!
 // It basically works just like level.read but calculates min/max/avg for that data level.read would return.
 // TODO: Make this DRY?
-func (l *level) stats(metric string, from, to int64, aggregation string) (*Stats, int64, int64, error) {
+func (l *level) stats(metric string, from, to int64, aggregation string) (Stats, int64, int64, error) {
 	if b, ok := l.metrics[metric]; ok {
 		return b.stats(from, to)
 	}
 
 	if len(l.children) == 0 {
-		return nil, 0, 0, errors.New("no data for that metric/level")
-	}
-
-	if len(l.children) == 1 {
-		for _, child := range l.children {
-			child.lock.Lock()
-			stats, from, to, err := child.stats(metric, from, to, aggregation)
-			child.lock.Unlock()
-			return stats, from, to, err
-		}
+		return Stats{}, 0, 0, ErrNoData
 	}
 
+	n := 0
 	samples := 0
-	avgSum, min, max := Float(0), Float(math.MaxFloat32), Float(-math.MaxFloat32)
+	avg, min, max := Float(0), Float(math.MaxFloat32), Float(-math.MaxFloat32)
 	for _, child := range l.children {
-		child.lock.Lock()
+		child.lock.RLock()
 		stats, cfrom, cto, err := child.stats(metric, from, to, aggregation)
-		child.lock.Unlock()
+		child.lock.RUnlock()
+
+		if err == ErrNoData {
+			continue
+		}
 
 		if err != nil {
-			return nil, 0, 0, err
+			return Stats{}, 0, 0, err
 		}
 
-		if cfrom != from || cto != to {
-			// See level.read for more on this
-			if samples == 0 {
-				from = cfrom
-				to = cto
-			} else {
-				return nil, 0, 0, errors.New("data for metrics at child levels does not align")
-			}
+		if n == 0 {
+			from = cfrom
+			to = cto
+		} else if cfrom != from || cto != to {
+			return Stats{}, 0, 0, ErrDataDoesNotAlign
 		}
 
 		samples += stats.Samples
-		avgSum += stats.Avg
+		avg += stats.Avg
 		min = Float(math.Min(float64(min), float64(stats.Min)))
 		max = Float(math.Max(float64(max), float64(stats.Max)))
+		n += 1
+	}
+
+	if n == 0 {
+		return Stats{}, 0, 0, ErrNoData
 	}
 
-	avg := avgSum
 	if aggregation == "avg" {
-		avg /= Float(len(l.children))
+		avg /= Float(n)
 	} else if aggregation != "sum" {
-		return nil, 0, 0, errors.New("invalid aggregation strategy: " + aggregation)
+		return Stats{}, 0, 0, errors.New("invalid aggregation strategy: " + aggregation)
 	}
 
-	return &Stats{
+	return Stats{
 		Samples: samples,
 		Avg:     avg,
 		Min:     min,
@@ -135,5 +132,6 @@ func (m *MemoryStore) Stats(selector []string, metric string, from, to int64) (*
 		return nil, 0, 0, errors.New("unkown metric: " + metric)
 	}
 
-	return l.stats(metric, from, to, minfo.Aggregation)
+	stats, from, to, err := l.stats(metric, from, to, minfo.Aggregation)
+	return &stats, from, to, err
 }