diff --git a/api.go b/api.go
index 66fa0ff..3fca3e5 100644
--- a/api.go
+++ b/api.go
@@ -62,8 +62,8 @@ func (data *ApiMetricData) PadDataWithNull(from, to int64, metric string) {
 		return
 	}
 
-	if (data.From / minfo.frequency) > (from / minfo.frequency) {
-		padfront := int((data.From / minfo.frequency) - (from / minfo.frequency))
+	if (data.From / minfo.Frequency) > (from / minfo.Frequency) {
+		padfront := int((data.From / minfo.Frequency) - (from / minfo.Frequency))
 		ndata := make([]Float, 0, padfront+len(data.Data))
 		for i := 0; i < padfront; i++ {
 			ndata = append(ndata, NaN)
@@ -101,7 +101,7 @@ func handleFree(rw http.ResponseWriter, r *http.Request) {
 	}
 
 	bodyDec := json.NewDecoder(r.Body)
-	var selectors []Selector
+	var selectors [][]string
 	err = bodyDec.Decode(&selectors)
 	if err != nil {
 		http.Error(rw, err.Error(), http.StatusBadRequest)
@@ -137,6 +137,7 @@ func handleWrite(rw http.ResponseWriter, r *http.Request) {
 
 	dec := lineprotocol.NewDecoderWithBytes(bytes)
 	if err := decodeLine(dec, r.URL.Query().Get("cluster")); err != nil {
+		log.Printf("/api/write error: %s", err.Error())
 		http.Error(rw, err.Error(), http.StatusBadRequest)
 		return
 	}
diff --git a/cc-metric-store.go b/cc-metric-store.go
index 25a3b21..f77457d 100644
--- a/cc-metric-store.go
+++ b/cc-metric-store.go
@@ -5,6 +5,7 @@ import (
 	"context"
 	"encoding/json"
 	"flag"
+	"fmt"
 	"log"
 	"os"
 	"os/signal"
@@ -15,12 +16,43 @@ import (
 	"github.com/google/gops/agent"
 )
 
+// For aggregation over multiple values at different cpus/sockets/..., not time!
+type AggregationStrategy int
+
+const (
+	NoAggregation AggregationStrategy = iota
+	SumAggregation
+	AvgAggregation
+)
+
+func (as *AggregationStrategy) UnmarshalJSON(data []byte) error {
+	var str string
+	if err := json.Unmarshal(data, &str); err != nil {
+		return err
+	}
+
+	switch str {
+	case "":
+		*as = NoAggregation
+	case "sum":
+		*as = SumAggregation
+	case "avg":
+		*as = AvgAggregation
+	default:
+		return fmt.Errorf("invalid aggregation strategy: %#v", str)
+	}
+	return nil
+}
+
 type MetricConfig struct {
 	// Interval in seconds at which measurements will arive.
 	Frequency int64 `json:"frequency"`
 
 	// Can be 'sum', 'avg' or null. Describes how to aggregate metrics from the same timestep over the hierarchy.
-	Aggregation string `json:"aggregation"`
+	Aggregation AggregationStrategy `json:"aggregation"`
+
+	// Private, used internally...
+	offset int
 }
 
 type HttpConfig struct {
@@ -107,7 +139,7 @@ func intervals(wg *sync.WaitGroup, ctx context.Context) {
 			case <-ticks:
 				t := time.Now().Add(-d)
 				log.Printf("start freeing buffers (older than %s)...\n", t.Format(time.RFC3339))
-				freed, err := memoryStore.Free(Selector{}, t.Unix())
+				freed, err := memoryStore.Free(nil, t.Unix())
 				if err != nil {
 					log.Printf("freeing up buffers failed: %s\n", err.Error())
 				} else {
diff --git a/lineprotocol.go b/lineprotocol.go
index 33562d8..f9d0b1b 100644
--- a/lineprotocol.go
+++ b/lineprotocol.go
@@ -114,9 +114,9 @@ func reorder(buf, prefix []byte) []byte {
 func decodeLine(dec *lineprotocol.Decoder, clusterDefault string) error {
 	// Reduce allocations in loop:
 	t := time.Now()
-	metrics := make([]Metric, 0, 10)
+	metric, metricBuf := Metric{}, make([]byte, 0, 16)
 	selector := make([]string, 0, 4)
-	typeBuf, subTypeBuf := make([]byte, 0, 20), make([]byte, 0)
+	typeBuf, subTypeBuf := make([]byte, 0, 16), make([]byte, 0)
 
 	// Optimize for the case where all lines in a "batch" are about the same
 	// cluster and host. By using `WriteToLevel` (level = host), we do not need
@@ -124,24 +124,21 @@ func decodeLine(dec *lineprotocol.Decoder, clusterDefault string) error {
 	var lvl *level = nil
 	var prevCluster, prevHost string = "", ""
 
+	var ok bool
 	for dec.Next() {
-		metrics = metrics[:0]
 		rawmeasurement, err := dec.Measurement()
 		if err != nil {
 			return err
 		}
 
-		// A more dense lp format if supported if the measurement is 'data'.
-		// In that case, the field keys are used as metric names.
-		if string(rawmeasurement) != "data" {
-			minfo, ok := memoryStore.metrics[string(rawmeasurement)]
-			if !ok {
-				continue
-			}
+		// Needs to be copied because another call to dec.* would
+		// invalidate the returned slice.
+		metricBuf = append(metricBuf[:0], rawmeasurement...)
 
-			metrics = append(metrics, Metric{
-				minfo: minfo,
-			})
+		// The go compiler optimizes map[string(byteslice)] lookups:
+		metric.mc, ok = memoryStore.metrics[string(rawmeasurement)]
+		if !ok {
+			continue
 		}
 
 		typeBuf, subTypeBuf := typeBuf[:0], subTypeBuf[:0]
@@ -176,6 +173,7 @@ func decodeLine(dec *lineprotocol.Decoder, clusterDefault string) error {
 					break
 				}
 
+				// We cannot be sure that the "type" tag comes before the "type-id" tag:
 				if len(typeBuf) == 0 {
 					typeBuf = append(typeBuf, val...)
 				} else {
@@ -184,6 +182,7 @@ func decodeLine(dec *lineprotocol.Decoder, clusterDefault string) error {
 			case "type-id":
 				typeBuf = append(typeBuf, val...)
 			case "subtype":
+				// We cannot be sure that the "subtype" tag comes before the "stype-id" tag:
 				if len(subTypeBuf) == 0 {
 					subTypeBuf = append(subTypeBuf, val...)
 				} else {
@@ -197,6 +196,7 @@ func decodeLine(dec *lineprotocol.Decoder, clusterDefault string) error {
 			}
 		}
 
+		// If the cluster or host changed, the lvl was set to nil
 		if lvl == nil {
 			selector = selector[:2]
 			selector[0], selector[1] = cluster, host
@@ -204,6 +204,7 @@ func decodeLine(dec *lineprotocol.Decoder, clusterDefault string) error {
 			prevCluster, prevHost = cluster, host
 		}
 
+		// subtypes:
 		selector = selector[:0]
 		if len(typeBuf) > 0 {
 			selector = append(selector, string(typeBuf)) // <- Allocation :(
@@ -212,71 +213,34 @@ func decodeLine(dec *lineprotocol.Decoder, clusterDefault string) error {
 			}
 		}
 
-		if len(metrics) == 0 {
-			for {
-				key, val, err := dec.NextField()
-				if err != nil {
-					return err
-				}
-
-				if key == nil {
-					break
-				}
-
-				var value Float
-				if val.Kind() == lineprotocol.Float {
-					value = Float(val.FloatV())
-				} else if val.Kind() == lineprotocol.Int {
-					value = Float(val.IntV())
-				} else {
-					return fmt.Errorf("unsupported value type in message: %s", val.Kind().String())
-				}
-
-				minfo, ok := memoryStore.metrics[string(key)]
-				if !ok {
-					continue
-				}
-
-				metrics = append(metrics, Metric{
-					minfo: minfo,
-					Value: value,
-				})
-			}
-		} else {
-			var value Float
-			for {
-				key, val, err := dec.NextField()
-				if err != nil {
-					return err
-				}
-
-				if key == nil {
-					break
-				}
-
-				if string(key) != "value" {
-					return fmt.Errorf("unkown field: '%s' (value: %#v)", string(key), val)
-				}
-
-				if val.Kind() == lineprotocol.Float {
-					value = Float(val.FloatV())
-				} else if val.Kind() == lineprotocol.Int {
-					value = Float(val.IntV())
-				} else {
-					return fmt.Errorf("unsupported value type in message: %s", val.Kind().String())
-				}
+		for {
+			key, val, err := dec.NextField()
+			if err != nil {
+				return err
 			}
 
-			metrics[0].Value = value
+			if key == nil {
+				break
+			}
+
+			if string(key) != "value" {
+				return fmt.Errorf("unkown field: '%s' (value: %#v)", string(key), val)
+			}
+
+			if val.Kind() == lineprotocol.Float {
+				metric.Value = Float(val.FloatV())
+			} else if val.Kind() == lineprotocol.Int {
+				metric.Value = Float(val.IntV())
+			} else {
+				return fmt.Errorf("unsupported value type in message: %s", val.Kind().String())
+			}
 		}
 
-		t, err = dec.Time(lineprotocol.Second, t)
-		if err != nil {
+		if t, err = dec.Time(lineprotocol.Second, t); err != nil {
 			return err
 		}
 
-		// log.Printf("write: %s (%v) -> %v\n", string(measurement), selector, value)
-		if err := memoryStore.WriteToLevel(lvl, selector, t.Unix(), metrics); err != nil {
+		if err := memoryStore.WriteToLevel(lvl, selector, t.Unix(), []Metric{metric}); err != nil {
 			return err
 		}
 	}
diff --git a/memstore.go b/memstore.go
index 017288d..023883b 100644
--- a/memstore.go
+++ b/memstore.go
@@ -192,35 +192,26 @@ func (b *buffer) read(from, to int64, data []Float) ([]Float, int64, int64, erro
 	return data[:i], from, t, nil
 }
 
-// Free up and free all buffers in the chain only containing data
-// older than `t`.
-func (b *buffer) free(t int64) (int, error) {
-	end := b.end()
-	if end < t && b.next != nil {
-		b.next.prev = nil
-		n := 0
-		for b != nil {
-			prev := b.prev
-			if prev != nil && prev.start > b.start {
-				panic("time travel?")
-			}
-
-			n += 1
-			// Buffers that come from the
-			// archive should not be reused.
-			if cap(b.data) == BUFFER_CAP {
-				bufferPool.Put(b)
-			}
-			b = prev
-		}
-		return n, nil
-	}
-
+// Returns true if this buffer needs to be freed.
+func (b *buffer) free(t int64) (delme bool, n int) {
 	if b.prev != nil {
-		return b.prev.free(t)
+		delme, m := b.prev.free(t)
+		n += m
+		if delme {
+			b.prev.next = nil
+			if cap(b.prev.data) == BUFFER_CAP {
+				bufferPool.Put(b.prev)
+			}
+			b.prev = nil
+		}
 	}
 
-	return 0, nil
+	end := b.end()
+	if end < t {
+		return true, n + 1
+	}
+
+	return false, n
 }
 
 // Call `callback` on every buffer that contains data in the range from `from` to `to`.
@@ -300,52 +291,54 @@ func (l *level) findLevelOrCreate(selector []string, nMetrics int) *level {
 	return child.findLevelOrCreate(selector[1:], nMetrics)
 }
 
-// For aggregation over multiple values at different cpus/sockets/..., not time!
-type AggregationStrategy int
+func (l *level) free(t int64) (int, error) {
+	l.lock.Lock()
+	defer l.lock.Unlock()
 
-const (
-	NoAggregation AggregationStrategy = iota
-	SumAggregation
-	AvgAggregation
-)
+	n := 0
+	for i, b := range l.metrics {
+		if b != nil {
+			delme, m := b.free(t)
+			n += m
+			if delme {
+				if cap(b.data) == BUFFER_CAP {
+					bufferPool.Put(b)
+				}
+				l.metrics[i] = nil
+			}
+		}
+	}
 
-type metricInfo struct {
-	offset      int
-	aggregation AggregationStrategy
-	frequency   int64
+	for _, l := range l.children {
+		m, err := l.free(t)
+		n += m
+		if err != nil {
+			return n, err
+		}
+	}
+
+	return n, nil
 }
 
 type MemoryStore struct {
 	root    level // root of the tree structure
-	metrics map[string]metricInfo
+	metrics map[string]MetricConfig
 }
 
 // Return a new, initialized instance of a MemoryStore.
 // Will panic if values in the metric configurations are invalid.
 func NewMemoryStore(metrics map[string]MetricConfig) *MemoryStore {
-	ms := make(map[string]metricInfo)
-
 	offset := 0
 	for key, config := range metrics {
-		aggregation := NoAggregation
-		if config.Aggregation == "sum" {
-			aggregation = SumAggregation
-		} else if config.Aggregation == "avg" {
-			aggregation = AvgAggregation
-		} else if config.Aggregation != "" {
-			panic("invalid aggregation strategy: " + config.Aggregation)
-		}
-
 		if config.Frequency == 0 {
 			panic("invalid frequency")
 		}
 
-		ms[key] = metricInfo{
+		metrics[key] = MetricConfig{
+			Frequency:   config.Frequency,
+			Aggregation: config.Aggregation,
 			offset:      offset,
-			aggregation: aggregation,
-			frequency:   config.Frequency,
 		}
-
 		offset += 1
 	}
 
@@ -354,7 +347,7 @@ func NewMemoryStore(metrics map[string]MetricConfig) *MemoryStore {
 			metrics:  make([]*buffer, len(metrics)),
 			children: make(map[string]*level),
 		},
-		metrics: ms,
+		metrics: metrics,
 	}
 }
 
@@ -363,10 +356,10 @@ func NewMemoryStore(metrics map[string]MetricConfig) *MemoryStore {
 func (m *MemoryStore) Write(selector []string, ts int64, metrics []Metric) error {
 	var ok bool
 	for i, metric := range metrics {
-		if metric.minfo.frequency == 0 {
-			metric.minfo, ok = m.metrics[metric.Name]
+		if metric.mc.Frequency == 0 {
+			metric.mc, ok = m.metrics[metric.Name]
 			if !ok {
-				metric.minfo.frequency = 0
+				metric.mc.Frequency = 0
 			}
 			metrics[i] = metric
 		}
@@ -386,15 +379,15 @@ func (m *MemoryStore) WriteToLevel(l *level, selector []string, ts int64, metric
 	defer l.lock.Unlock()
 
 	for _, metric := range metrics {
-		if metric.minfo.frequency == 0 {
+		if metric.mc.Frequency == 0 {
 			continue
 		}
 
-		b := l.metrics[metric.minfo.offset]
+		b := l.metrics[metric.mc.offset]
 		if b == nil {
 			// First write to this metric and level
-			b = newBuffer(ts, metric.minfo.frequency)
-			l.metrics[metric.minfo.offset] = b
+			b = newBuffer(ts, metric.mc.Frequency)
+			l.metrics[metric.mc.offset] = b
 		}
 
 		nb, err := b.write(ts, metric.Value)
@@ -404,7 +397,7 @@ func (m *MemoryStore) WriteToLevel(l *level, selector []string, ts int64, metric
 
 		// Last write created a new buffer...
 		if b != nb {
-			l.metrics[metric.minfo.offset] = nb
+			l.metrics[metric.mc.offset] = nb
 		}
 	}
 	return nil
@@ -424,7 +417,7 @@ func (m *MemoryStore) Read(selector Selector, metric string, from, to int64) ([]
 		return nil, 0, 0, errors.New("unkown metric: " + metric)
 	}
 
-	n, data := 0, make([]Float, (to-from)/minfo.frequency+1)
+	n, data := 0, make([]Float, (to-from)/minfo.Frequency+1)
 	err := m.root.findBuffers(selector, minfo.offset, func(b *buffer) error {
 		cdata, cfrom, cto, err := b.read(from, to, data)
 		if err != nil {
@@ -434,7 +427,17 @@ func (m *MemoryStore) Read(selector Selector, metric string, from, to int64) ([]
 		if n == 0 {
 			from, to = cfrom, cto
 		} else if from != cfrom || to != cto || len(data) != len(cdata) {
-			return ErrDataDoesNotAlign
+			missingfront, missingback := int((from-cfrom)/minfo.Frequency), int((to-cto)/minfo.Frequency)
+			if missingfront != 0 {
+				return ErrDataDoesNotAlign
+			}
+
+			cdata = cdata[0 : len(cdata)-missingback]
+			if len(cdata) != len(data) {
+				return ErrDataDoesNotAlign
+			}
+
+			from, to = cfrom, cto
 		}
 
 		data = cdata
@@ -447,12 +450,12 @@ func (m *MemoryStore) Read(selector Selector, metric string, from, to int64) ([]
 	} else if n == 0 {
 		return nil, 0, 0, errors.New("metric or host not found")
 	} else if n > 1 {
-		if minfo.aggregation == AvgAggregation {
+		if minfo.Aggregation == AvgAggregation {
 			normalize := 1. / Float(n)
 			for i := 0; i < len(data); i++ {
 				data[i] *= normalize
 			}
-		} else if minfo.aggregation != SumAggregation {
+		} else if minfo.Aggregation != SumAggregation {
 			return nil, 0, 0, errors.New("invalid aggregation")
 		}
 	}
@@ -462,14 +465,8 @@ func (m *MemoryStore) Read(selector Selector, metric string, from, to int64) ([]
 
 // Release all buffers for the selected level and all its children that contain only
 // values older than `t`.
-func (m *MemoryStore) Free(selector Selector, t int64) (int, error) {
-	n := 0
-	err := m.root.findBuffers(selector, -1, func(b *buffer) error {
-		m, err := b.free(t)
-		n += m
-		return err
-	})
-	return n, err
+func (m *MemoryStore) Free(selector []string, t int64) (int, error) {
+	return m.GetLevel(selector).free(t)
 }
 
 func (m *MemoryStore) FreeAll() error {
diff --git a/memstore_test.go b/memstore_test.go
index 5c4ab52..ef02166 100644
--- a/memstore_test.go
+++ b/memstore_test.go
@@ -201,8 +201,8 @@ func TestMemoryStoreMissingDatapoints(t *testing.T) {
 func TestMemoryStoreAggregation(t *testing.T) {
 	count := 3000
 	store := NewMemoryStore(map[string]MetricConfig{
-		"a": {Frequency: 1, Aggregation: "sum"},
-		"b": {Frequency: 2, Aggregation: "avg"},
+		"a": {Frequency: 1, Aggregation: SumAggregation},
+		"b": {Frequency: 2, Aggregation: AvgAggregation},
 	})
 
 	for i := 0; i < count; i++ {
@@ -269,7 +269,7 @@ func TestMemoryStoreStats(t *testing.T) {
 	count := 3000
 	store := NewMemoryStore(map[string]MetricConfig{
 		"a": {Frequency: 1},
-		"b": {Frequency: 1, Aggregation: "avg"},
+		"b": {Frequency: 1, Aggregation: AvgAggregation},
 	})
 
 	sel1 := []string{"cluster", "host1"}
@@ -415,7 +415,7 @@ func TestMemoryStoreFree(t *testing.T) {
 		}
 	}
 
-	n, err := store.Free(Selector{{String: "cluster"}, {String: "host"}}, int64(BUFFER_CAP*2)+100)
+	n, err := store.Free([]string{"cluster", "host"}, int64(BUFFER_CAP*2)+100)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -501,7 +501,7 @@ func BenchmarkMemoryStoreAggregation(b *testing.B) {
 	b.StopTimer()
 	count := 2000
 	store := NewMemoryStore(map[string]MetricConfig{
-		"flops_any": {Frequency: 1, Aggregation: "avg"},
+		"flops_any": {Frequency: 1, Aggregation: AvgAggregation},
 	})
 
 	sel := []string{"testcluster", "host123", "cpu0"}
diff --git a/selector.go b/selector.go
index a2ff52e..de17ed5 100644
--- a/selector.go
+++ b/selector.go
@@ -55,20 +55,9 @@ func (l *level) findBuffers(selector Selector, offset int, f func(b *buffer) err
 	defer l.lock.RUnlock()
 
 	if len(selector) == 0 {
-		if offset == -1 {
-			for _, b := range l.metrics {
-				if b != nil {
-					err := f(b)
-					if err != nil {
-						return err
-					}
-				}
-			}
-		} else {
-			b := l.metrics[offset]
-			if b != nil {
-				return f(b)
-			}
+		b := l.metrics[offset]
+		if b != nil {
+			return f(b)
 		}
 
 		for _, lvl := range l.children {
diff --git a/stats.go b/stats.go
index 2e56dd5..510891b 100644
--- a/stats.go
+++ b/stats.go
@@ -103,9 +103,9 @@ func (m *MemoryStore) Stats(selector Selector, metric string, from, to int64) (*
 		return nil, 0, 0, ErrNoData
 	}
 
-	if minfo.aggregation == AvgAggregation {
+	if minfo.Aggregation == AvgAggregation {
 		avg /= Float(n)
-	} else if n > 1 && minfo.aggregation != SumAggregation {
+	} else if n > 1 && minfo.Aggregation != SumAggregation {
 		return nil, 0, 0, errors.New("invalid aggregation")
 	}