diff --git a/retrieval/targetpool.go b/retrieval/targetpool.go
index 89cc4d0aed..2b161b45e4 100644
--- a/retrieval/targetpool.go
+++ b/retrieval/targetpool.go
@@ -78,7 +78,7 @@ func (p *TargetPool) Run() {
 	}
 }
 
-func (p TargetPool) Stop() {
+func (p *TargetPool) Stop() {
 	stopped := make(chan bool)
 	p.done <- stopped
 	<-stopped
diff --git a/rules/helpers_test.go b/rules/helpers_test.go
index 69836978d3..72bfeb36c9 100644
--- a/rules/helpers_test.go
+++ b/rules/helpers_test.go
@@ -52,7 +52,7 @@ func getTestVectorFromTestMatrix(matrix ast.Matrix) ast.Vector {
 	return vector
 }
 
-func storeMatrix(storage storage_ng.Storage, matrix ast.Matrix) {
+func storeMatrix(storage local.Storage, matrix ast.Matrix) {
 	pendingSamples := clientmodel.Samples{}
 	for _, sampleSet := range matrix {
 		for _, sample := range sampleSet.Values {
diff --git a/rules/rules_test.go b/rules/rules_test.go
index 083f6dd094..d5e60e9716 100644
--- a/rules/rules_test.go
+++ b/rules/rules_test.go
@@ -52,8 +52,8 @@ func vectorComparisonString(expected []string, actual []string) string {
 		separator)
 }
 
-func newTestStorage(t testing.TB) (storage storage_ng.Storage, closer test.Closer) {
-	storage, closer = storage_ng.NewTestStorage(t)
+func newTestStorage(t testing.TB) (storage local.Storage, closer test.Closer) {
+	storage, closer = local.NewTestStorage(t)
 	storeMatrix(storage, testMatrix)
 	return storage, closer
 }
diff --git a/storage/local/locker.go b/storage/local/locker.go
index bbac094e05..c0ac876543 100644
--- a/storage/local/locker.go
+++ b/storage/local/locker.go
@@ -6,93 +6,38 @@ import (
 	clientmodel "github.com/prometheus/client_golang/model"
 )
 
-// fingerprintLock allows locking exactly one fingerprint. When refCount is 0
-// after the mutex is unlocked, the fingerprintLock is discarded from the
-// fingerprintLocker.
-type fingerprintLock struct {
-	sync.Mutex
-	refCount int
-}
-
-// fingerprintLocker allows locking individual fingerprints in such a manner
-// that the lock only exists and uses memory while it is being held (or waiting
-// to be acquired) by at least one party.
-//
-// TODO: This could be implemented as just a fixed number n of locks, assigned
-// based on the fingerprint % n. There can be collisons, but they would
-// statistically rarely matter (if n is much larger than the number of
-// goroutines requiring locks concurrently). Only problem is locking of two
-// different fingerprints by the same goroutine.
+// fingerprintLocker allows locking individual fingerprints. To limit the number
+// of mutexes needed for that, only a fixed number of mutexes are
+// allocated. Fingerprints to be locked are assigned to those pre-allocated
+// mutexes by their value. (Note that fingerprints are calculated by a hash
+// function, so that an approximately equal distribution over the mutexes is
+// expected, even without additional hashing of the fingerprint value.)
+// Collisions are not detected. If two fingerprints get assigned to the same
+// mutex, only one of them can be locked at the same time. As long as the number
+// of pre-allocated mutexes is much larger than the number of goroutines
+// requiring a fingerprint lock concurrently, the loss in efficiency is
+// small. However, a goroutine must never lock more than one fingerprint at the
+// same time. (In that case a collision would try to acquire the same mutex
+// twice).
 type fingerprintLocker struct {
-	mtx        sync.Mutex
-	fpLocks    map[clientmodel.Fingerprint]*fingerprintLock
-	fpLockPool []*fingerprintLock
+	fpMtxs    []sync.Mutex
+	numFpMtxs uint
 }
 
 // newFingerprintLocker returns a new fingerprintLocker ready for use.
 func newFingerprintLocker(preallocatedMutexes int) *fingerprintLocker {
-	lockPool := make([]*fingerprintLock, preallocatedMutexes)
-	for i := range lockPool {
-		lockPool[i] = &fingerprintLock{}
-	}
 	return &fingerprintLocker{
-		fpLocks:    map[clientmodel.Fingerprint]*fingerprintLock{},
-		fpLockPool: lockPool,
+		make([]sync.Mutex, preallocatedMutexes),
+		uint(preallocatedMutexes),
 	}
 }
 
-// getLock either returns an existing fingerprintLock from a pool, or allocates
-// a new one if the pool is depleted.
-func (l *fingerprintLocker) getLock() *fingerprintLock {
-	return l.fpLockPool[0]
-	if len(l.fpLockPool) == 0 {
-		return &fingerprintLock{}
-	}
-
-	lock := l.fpLockPool[len(l.fpLockPool)-1]
-	l.fpLockPool = l.fpLockPool[:len(l.fpLockPool)-1]
-	return lock
-}
-
-// putLock either stores a fingerprintLock back in the pool, or throws it away
-// if the pool is full.
-func (l *fingerprintLocker) putLock(fpl *fingerprintLock) {
-	if len(l.fpLockPool) == cap(l.fpLockPool) {
-		return
-	}
-
-	l.fpLockPool = l.fpLockPool[:len(l.fpLockPool)+1]
-	l.fpLockPool[len(l.fpLockPool)-1] = fpl
-}
-
 // Lock locks the given fingerprint.
 func (l *fingerprintLocker) Lock(fp clientmodel.Fingerprint) {
-	l.mtx.Lock()
-
-	fpLock, ok := l.fpLocks[fp]
-	if ok {
-		fpLock.refCount++
-	} else {
-		fpLock = l.getLock()
-		l.fpLocks[fp] = fpLock
-	}
-
-	l.mtx.Unlock()
-	fpLock.Lock()
+	l.fpMtxs[uint(fp)%l.numFpMtxs].Lock()
 }
 
 // Unlock unlocks the given fingerprint.
 func (l *fingerprintLocker) Unlock(fp clientmodel.Fingerprint) {
-	l.mtx.Lock()
-	defer l.mtx.Unlock()
-
-	fpLock := l.fpLocks[fp]
-	fpLock.Unlock()
-
-	if fpLock.refCount == 0 {
-		delete(l.fpLocks, fp)
-		l.putLock(fpLock)
-	} else {
-		fpLock.refCount--
-	}
+	l.fpMtxs[uint(fp)%l.numFpMtxs].Unlock()
 }
diff --git a/storage/local/persistence.go b/storage/local/persistence.go
index 830dd94349..83e48e4170 100644
--- a/storage/local/persistence.go
+++ b/storage/local/persistence.go
@@ -358,7 +358,7 @@ func (p *persistence) loadChunkDescs(fp clientmodel.Fingerprint, beforeTime clie
 // - Make sure the length of the seriesMap doesn't change during the runtime.
 // - Lock the fingerprints while persisting unpersisted head chunks.
 // - Write to temporary file and only rename after successfully finishing.
-func (p *persistence) persistSeriesMapAndHeads(fingerprintToSeries seriesMap) error {
+func (p *persistence) persistSeriesMapAndHeads(fingerprintToSeries *seriesMap) error {
 	f, err := os.OpenFile(p.headsPath(), os.O_WRONLY|os.O_TRUNC|os.O_CREATE, 0640)
 	if err != nil {
 		return err
@@ -431,54 +431,54 @@ func (p *persistence) persistSeriesMapAndHeads(fingerprintToSeries seriesMap) er
 // open (non-full) head chunks. Only call this method during start-up while
 // nothing else is running in storage land. This method is utterly
 // goroutine-unsafe.
-func (p *persistence) loadSeriesMapAndHeads() (seriesMap, error) {
+func (p *persistence) loadSeriesMapAndHeads() (*seriesMap, error) {
 	f, err := os.Open(p.headsPath())
 	if os.IsNotExist(err) {
 		return newSeriesMap(), nil
 	}
 	if err != nil {
-		return seriesMap{}, err
+		return nil, err
 	}
 	defer f.Close()
 	r := bufio.NewReaderSize(f, fileBufSize)
 
 	buf := make([]byte, len(headsMagicString))
 	if _, err := io.ReadFull(r, buf); err != nil {
-		return seriesMap{}, err
+		return nil, err
 	}
 	magic := string(buf)
 	if magic != headsMagicString {
-		return seriesMap{}, fmt.Errorf(
+		return nil, fmt.Errorf(
 			"unexpected magic string, want %q, got %q",
 			headsMagicString, magic,
 		)
 	}
 	if version, err := binary.ReadVarint(r); version != headsFormatVersion || err != nil {
-		return seriesMap{}, fmt.Errorf("unknown heads format version, want %d", headsFormatVersion)
+		return nil, fmt.Errorf("unknown heads format version, want %d", headsFormatVersion)
 	}
 	numSeries, err := binary.ReadVarint(r)
 	if err != nil {
-		return seriesMap{}, err
+		return nil, err
 	}
 	fingerprintToSeries := make(map[clientmodel.Fingerprint]*memorySeries, numSeries)
 
 	for ; numSeries > 0; numSeries-- {
 		seriesFlags, err := r.ReadByte()
 		if err != nil {
-			return seriesMap{}, err
+			return nil, err
 		}
 		headChunkPersisted := seriesFlags&flagHeadChunkPersisted != 0
 		fp, err := codable.DecodeUint64(r)
 		if err != nil {
-			return seriesMap{}, err
+			return nil, err
 		}
 		var metric codable.Metric
 		if err := metric.UnmarshalFromReader(r); err != nil {
-			return seriesMap{}, err
+			return nil, err
 		}
 		numChunkDescs, err := binary.ReadVarint(r)
 		if err != nil {
-			return seriesMap{}, err
+			return nil, err
 		}
 		chunkDescs := make(chunkDescs, numChunkDescs)
 
@@ -486,11 +486,11 @@ func (p *persistence) loadSeriesMapAndHeads() (seriesMap, error) {
 			if headChunkPersisted || i < numChunkDescs-1 {
 				firstTime, err := binary.ReadVarint(r)
 				if err != nil {
-					return seriesMap{}, err
+					return nil, err
 				}
 				lastTime, err := binary.ReadVarint(r)
 				if err != nil {
-					return seriesMap{}, err
+					return nil, err
 				}
 				chunkDescs[i] = &chunkDesc{
 					firstTimeField: clientmodel.Timestamp(firstTime),
@@ -500,11 +500,11 @@ func (p *persistence) loadSeriesMapAndHeads() (seriesMap, error) {
 				// Non-persisted head chunk.
 				chunkType, err := r.ReadByte()
 				if err != nil {
-					return seriesMap{}, err
+					return nil, err
 				}
 				chunk := chunkForType(chunkType)
 				if err := chunk.unmarshal(r); err != nil {
-					return seriesMap{}, err
+					return nil, err
 				}
 				chunkDescs[i] = &chunkDesc{
 					chunk:    chunk,
@@ -520,7 +520,7 @@ func (p *persistence) loadSeriesMapAndHeads() (seriesMap, error) {
 			headChunkPersisted: headChunkPersisted,
 		}
 	}
-	return seriesMap{m: fingerprintToSeries}, nil
+	return &seriesMap{m: fingerprintToSeries}, nil
 }
 
 // dropChunks deletes all chunks from a series whose last sample time is before
diff --git a/storage/local/series.go b/storage/local/series.go
index 4cc64d6e92..efc10e54e4 100644
--- a/storage/local/series.go
+++ b/storage/local/series.go
@@ -38,12 +38,12 @@ type seriesMap struct {
 
 // newSeriesMap returns a newly allocated empty seriesMap. To create a seriesMap
 // based on a prefilled map, use an explicit initializer.
-func newSeriesMap() seriesMap {
-	return seriesMap{m: make(map[clientmodel.Fingerprint]*memorySeries)}
+func newSeriesMap() *seriesMap {
+	return &seriesMap{m: make(map[clientmodel.Fingerprint]*memorySeries)}
 }
 
 // length returns the number of mappings in the seriesMap.
-func (sm seriesMap) length() int {
+func (sm *seriesMap) length() int {
 	sm.mtx.RLock()
 	defer sm.mtx.RUnlock()
 
@@ -52,7 +52,7 @@ func (sm seriesMap) length() int {
 
 // get returns a memorySeries for a fingerprint. Return values have the same
 // semantics as the native Go map.
-func (sm seriesMap) get(fp clientmodel.Fingerprint) (s *memorySeries, ok bool) {
+func (sm *seriesMap) get(fp clientmodel.Fingerprint) (s *memorySeries, ok bool) {
 	sm.mtx.RLock()
 	defer sm.mtx.RUnlock()
 
@@ -61,7 +61,7 @@ func (sm seriesMap) get(fp clientmodel.Fingerprint) (s *memorySeries, ok bool) {
 }
 
 // put adds a mapping to the seriesMap.
-func (sm seriesMap) put(fp clientmodel.Fingerprint, s *memorySeries) {
+func (sm *seriesMap) put(fp clientmodel.Fingerprint, s *memorySeries) {
 	sm.mtx.Lock()
 	defer sm.mtx.Unlock()
 
@@ -69,7 +69,7 @@ func (sm seriesMap) put(fp clientmodel.Fingerprint, s *memorySeries) {
 }
 
 // del removes a mapping from the series Map.
-func (sm seriesMap) del(fp clientmodel.Fingerprint) {
+func (sm *seriesMap) del(fp clientmodel.Fingerprint) {
 	sm.mtx.Lock()
 	defer sm.mtx.Unlock()
 
@@ -83,7 +83,7 @@ func (sm seriesMap) del(fp clientmodel.Fingerprint) {
 // for iterating over a map with a 'range' clause. However, if the next element
 // in iteration order is removed after the current element has been received
 // from the channel, it will still be produced by the channel.
-func (sm seriesMap) iter() <-chan fingerprintSeriesPair {
+func (sm *seriesMap) iter() <-chan fingerprintSeriesPair {
 	ch := make(chan fingerprintSeriesPair)
 	go func() {
 		sm.mtx.RLock()
@@ -105,7 +105,7 @@ func (sm seriesMap) iter() <-chan fingerprintSeriesPair {
 // for iterating over a map with a 'range' clause. However, if the next element
 // in iteration order is removed after the current element has been received
 // from the channel, it will still be produced by the channel.
-func (sm seriesMap) fpIter() <-chan clientmodel.Fingerprint {
+func (sm *seriesMap) fpIter() <-chan clientmodel.Fingerprint {
 	ch := make(chan clientmodel.Fingerprint)
 	go func() {
 		sm.mtx.RLock()
diff --git a/storage/local/storage.go b/storage/local/storage.go
index 6b5d031dac..738dbbf612 100644
--- a/storage/local/storage.go
+++ b/storage/local/storage.go
@@ -41,7 +41,7 @@ type memorySeriesStorage struct {
 	persistDone chan bool
 	stopServing chan chan<- bool
 
-	fingerprintToSeries seriesMap
+	fingerprintToSeries *seriesMap
 
 	memoryEvictionInterval time.Duration
 	memoryRetentionPeriod  time.Duration
diff --git a/templates/templates_test.go b/templates/templates_test.go
index 0b20e93b7c..ae817aa143 100644
--- a/templates/templates_test.go
+++ b/templates/templates_test.go
@@ -152,7 +152,7 @@ func TestTemplateExpansion(t *testing.T) {
 
 	time := clientmodel.Timestamp(0)
 
-	storage, closer := storage_ng.NewTestStorage(t)
+	storage, closer := local.NewTestStorage(t)
 	defer closer.Close()
 	storage.AppendSamples(clientmodel.Samples{
 		{