diff --git a/sinks/compactor.go b/sinks/compactor.go
new file mode 100644
index 0000000..90dd2bb
--- /dev/null
+++ b/sinks/compactor.go
@@ -0,0 +1,134 @@
+package sinks
+
+import (
+	"errors"
+	"fmt"
+	"sort"
+	"time"
+
+	ilp "github.com/ClusterCockpit/cc-metric-collector/internal/ccMetric"
+	lp "github.com/influxdata/line-protocol"
+)
+
+// A node in a tree structured by tags
+type compactorEntry struct {
+	tagKey   string                     // The tag key all points share in this sub-tree.
+	tagValue string                     // The tag value all points share in this sub-tree.
+	points   map[int64][]ilp.CCMetric   // The points with those keys (only), grouped by points where the time is the same.
+	entries  map[string]*compactorEntry // Points with even more keys go here, grouped by those keys.
+}
+
+func (ce *compactorEntry) read(lines []ilp.CCMetric, tags []lp.Tag) ([]ilp.CCMetric, error) {
+	for t, points := range ce.points {
+		fields := make(map[string]interface{})
+		for _, point := range points {
+			if val, ok := point.GetField("value"); ok {
+				fields[point.Name()] = val
+			} else {
+				return nil, errors.New("only field expected is 'value'")
+			}
+		}
+
+		p, err := ilp.New("data", nil, nil, fields, time.Unix(t, 0))
+		if err != nil {
+			return nil, err
+		}
+		for _, tag := range tags {
+			p.AddTag(tag.Key, tag.Value)
+		}
+
+		lines = append(lines, p)
+	}
+
+	for _, e := range ce.entries {
+		var err error
+		lines, err = e.read(lines, append(tags, lp.Tag{
+			Key:   e.tagKey,
+			Value: e.tagValue,
+		}))
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	return lines, nil
+}
+
+type Compactor struct {
+	wrapped Sink
+	n       int
+	root    compactorEntry
+}
+
+var _ Sink = (*Compactor)(nil)
+
+func NewCompactor(name string, wrapped Sink) (Sink, error) {
+	c := &Compactor{
+		wrapped: wrapped,
+		root: compactorEntry{
+			points:  make(map[int64][]ilp.CCMetric),
+			entries: make(map[string]*compactorEntry),
+		},
+	}
+	return c, nil
+}
+
+func (c *Compactor) Write(point ilp.CCMetric) error {
+	taglist := make([]lp.Tag, 0)
+	for k, v := range point.Tags() {
+		taglist = append(taglist, lp.Tag{Key: k, Value: v})
+	}
+
+	sort.Slice(taglist, func(i, j int) bool {
+		a, b := taglist[i], taglist[j]
+		return a.Key < b.Key
+	})
+
+	e := &c.root
+	for _, tag := range taglist {
+		mapkey := tag.Key + ":" + tag.Value
+		ce, ok := e.entries[mapkey]
+		if !ok {
+			ce = &compactorEntry{
+				tagKey:   tag.Key,
+				tagValue: tag.Value,
+				points:   make(map[int64][]ilp.CCMetric),
+				entries:  make(map[string]*compactorEntry),
+			}
+			e.entries[mapkey] = ce
+		}
+		e = ce
+	}
+
+	t := point.Time().Unix()
+	c.n += 1
+	e.points[t] = append(e.points[t], point)
+	return nil
+}
+
+func (c *Compactor) Flush() error {
+	points := make([]ilp.CCMetric, 0, c.n)
+	points, err := c.root.read(points, make([]lp.Tag, 0, 5))
+	if err != nil {
+		return err
+	}
+
+	for _, p := range points {
+		if err := c.wrapped.Write(p); err != nil {
+			return err
+		}
+	}
+
+	c.n = 0
+	c.root.points = make(map[int64][]ilp.CCMetric)
+	c.root.entries = make(map[string]*compactorEntry)
+	return c.wrapped.Flush()
+}
+
+func (c *Compactor) Close() {
+	c.wrapped.Close()
+}
+
+func (c *Compactor) Name() string {
+	return fmt.Sprintf("%s (compacted)", c.wrapped.Name())
+}
diff --git a/sinks/httpSink.go b/sinks/httpSink.go
index 962c2d7..c0a99ce 100644
--- a/sinks/httpSink.go
+++ b/sinks/httpSink.go
@@ -21,6 +21,7 @@ type HttpSinkConfig struct {
 	Timeout         string `json:"timeout,omitempty"`
 	IdleConnTimeout string `json:"idle_connection_timeout,omitempty"`
 	FlushDelay      string `json:"flush_delay,omitempty"`
+	MaxRetries      int    `json:"max_retries,omitempty"`
 }
 
 type HttpSink struct {
@@ -37,76 +38,75 @@ type HttpSink struct {
 }
 
 func (s *HttpSink) Write(m lp.CCMetric) error {
-	if s.buffer.Len() == 0 && s.flushDelay != 0 {
-		// This is the first write since the last flush, start the flushTimer!
-		if s.flushTimer != nil && s.flushTimer.Stop() {
-			cclog.ComponentDebug(s.name, "unexpected: the flushTimer was already running?")
-		}
-
-		// Run a batched flush for all lines that have arrived in the last second
-		s.flushTimer = time.AfterFunc(s.flushDelay, func() {
-			if err := s.Flush(); err != nil {
-				cclog.ComponentError(s.name, "flush failed:", err.Error())
-			}
-		})
-	}
-
 	p := m.ToPoint(s.meta_as_tags)
-
 	s.lock.Lock()
+	firstWriteOfBatch := s.buffer.Len() == 0
 	_, err := s.encoder.Encode(p)
-	s.lock.Unlock() // defer does not work here as Flush() takes the lock as well
-
+	s.lock.Unlock()
 	if err != nil {
 		cclog.ComponentError(s.name, "encoding failed:", err.Error())
 		return err
 	}
 
-	// Flush synchronously if "flush_delay" is zero
 	if s.flushDelay == 0 {
 		return s.Flush()
 	}
 
-	return err
+	if firstWriteOfBatch {
+		if s.flushTimer == nil {
+			s.flushTimer = time.AfterFunc(s.flushDelay, func() {
+				if err := s.Flush(); err != nil {
+					cclog.ComponentError(s.name, "flush failed:", err.Error())
+				}
+			})
+		} else {
+			s.flushTimer.Reset(s.flushDelay)
+		}
+	}
+
+	return nil
 }
 
 func (s *HttpSink) Flush() error {
-	// buffer is read by client.Do, prevent concurrent modifications
+	// Own lock for as short as possible: the time it takes to copy the buffer.
 	s.lock.Lock()
-	defer s.lock.Unlock()
-
-	// Do not flush empty buffer
-	if s.buffer.Len() == 0 {
+	buf := make([]byte, s.buffer.Len())
+	copy(buf, s.buffer.Bytes())
+	s.buffer.Reset()
+	s.lock.Unlock()
+	if len(buf) == 0 {
 		return nil
 	}
 
-	// Create new request to send buffer
-	req, err := http.NewRequest(http.MethodPost, s.config.URL, s.buffer)
-	if err != nil {
-		cclog.ComponentError(s.name, "failed to create request:", err.Error())
-		return err
-	}
+	var res *http.Response
+	for i := 0; i < s.config.MaxRetries; i++ {
+		// Create new request to send buffer
+		req, err := http.NewRequest(http.MethodPost, s.config.URL, bytes.NewReader(buf))
+		if err != nil {
+			cclog.ComponentError(s.name, "failed to create request:", err.Error())
+			return err
+		}
 
-	// Set authorization header
-	if len(s.config.JWT) != 0 {
-		req.Header.Set("Authorization", fmt.Sprintf("Bearer %s", s.config.JWT))
-	}
+		// Set authorization header
+		if len(s.config.JWT) != 0 {
+			req.Header.Set("Authorization", fmt.Sprintf("Bearer %s", s.config.JWT))
+		}
 
-	// Send
-	res, err := s.client.Do(req)
+		// Do request
+		res, err = s.client.Do(req)
+		if err != nil {
+			cclog.ComponentError(s.name, "transport/tcp error:", err.Error())
+			// Wait between retries
+			time.Sleep(time.Duration(i+1) * time.Second)
+			continue
+		}
 
-	// Clear buffer
-	s.buffer.Reset()
-
-	// Handle transport/tcp errors
-	if err != nil {
-		cclog.ComponentError(s.name, "transport/tcp error:", err.Error())
-		return err
+		break
 	}
 
 	// Handle application errors
 	if res.StatusCode != http.StatusOK {
-		err = errors.New(res.Status)
+		err := errors.New(res.Status)
 		cclog.ComponentError(s.name, "application error:", err.Error())
 		return err
 	}
@@ -129,6 +129,7 @@ func NewHttpSink(name string, config json.RawMessage) (Sink, error) {
 	s.config.IdleConnTimeout = "120s" // should be larger than the measurement interval.
 	s.config.Timeout = "5s"
 	s.config.FlushDelay = "5s"
+	s.config.MaxRetries = 3
 
 	// Read config
 	if len(config) > 0 {
diff --git a/sinks/natsSink.go b/sinks/natsSink.go
index 3e2e728..4d43454 100644
--- a/sinks/natsSink.go
+++ b/sinks/natsSink.go
@@ -21,7 +21,7 @@ type NatsSinkConfig struct {
 	Subject    string `json:"subject,omitempty"`
 	User       string `json:"user,omitempty"`
 	Password   string `json:"password,omitempty"`
-	FlushDelay string `json:"flush-delay,omitempty"`
+	FlushDelay string `json:"flush_delay,omitempty"`
 }
 
 type NatsSink struct {
@@ -87,6 +87,10 @@ func (s *NatsSink) Flush() error {
 	s.buffer.Reset()
 	s.lock.Unlock()
 
+	if len(buf) == 0 {
+		return nil
+	}
+
 	if err := s.client.Publish(s.config.Subject, buf); err != nil {
 		cclog.ComponentError(s.name, "Flush:", err.Error())
 		return err