Index-persistence switched from gob to a hand-coded solution.

Change-Id: Ib4ec42535bd08df16d34d4774bb638e35c5a1841

storage/local/delta.go

@@ -362,11 +362,11 @@ func (it *deltaEncodedChunkIterator) getValueAtTime(t clientmodel.Timestamp) met
 	case it.chunk.len():
 		return metric.Values{*it.chunk.valueAtIndex(it.chunk.len() - 1)}
 	default:
-		if v := it.chunk.valueAtIndex(i); v.Timestamp.Equal(t) {
+		v := it.chunk.valueAtIndex(i)
+		if v.Timestamp.Equal(t) {
 			return metric.Values{*v}
-		} else {
-			return metric.Values{*it.chunk.valueAtIndex(i - 1), *v}
 		}
+		return metric.Values{*it.chunk.valueAtIndex(i - 1), *v}
 	}
 }
 

storage/local/interface.go

@@ -47,7 +47,9 @@ type SeriesIterator interface {
 type Persistence interface {
 	// PersistChunk persists a single chunk of a series.
 	PersistChunk(clientmodel.Fingerprint, chunk) error
-	// PersistIndexes persists a Prometheus server's timeseries indexes.
+	// PersistIndexes persists a Prometheus server's timeseries indexes. It
+	// is the caller's responsibility to not modify indexes while persisting
+	// is underway, and to not call this method multiple times concurrently.
 	PersistIndexes(i *Indexes) error
 	// PersistHeads persists all open (non-full) head chunks.
 	PersistHeads(map[clientmodel.Fingerprint]*memorySeries) error
@@ -64,7 +66,9 @@ type Persistence interface {
 	LoadChunkDescs(fp clientmodel.Fingerprint, beforeTime clientmodel.Timestamp) (chunkDescs, error)
 	// LoadHeads loads all open (non-full) head chunks.
 	LoadHeads(map[clientmodel.Fingerprint]*memorySeries) error
-	// LoadIndexes loads and returns all timeseries indexes.
+	// LoadIndexes loads and returns all timeseries indexes. It is the
+	// caller's responsibility to not modify indexes while loading is
+	// underway, and to not call this method multiple times concurrently.
 	LoadIndexes() (*Indexes, error)
 }
 

storage/local/persistence.go

@@ -24,8 +24,12 @@ import (
 const (
 	seriesFileName     = "series.db"
 	seriesTempFileName = "series.db.tmp"
-	indexFileName      = "index.db"
 	headsFileName      = "heads.db"
+	indexFileName      = "index.db"
+
+	indexFormatVersion = 1
+	indexMagicString   = "PrometheusIndexes"
+	indexBufSize       = 1 << 15 // 32kiB. TODO: Tweak.
 
 	chunkHeaderLen             = 17
 	chunkHeaderTypeOffset      = 0
@@ -40,6 +44,7 @@ const (
 type diskPersistence struct {
 	basePath string
 	chunkLen int
+	buf      []byte // Staging space for persisting indexes.
 }
 
 func NewDiskPersistence(basePath string, chunkLen int) (Persistence, error) {
@@ -53,6 +58,7 @@ func NewDiskPersistence(basePath string, chunkLen int) (Persistence, error) {
 	return &diskPersistence{
 		basePath: basePath,
 		chunkLen: chunkLen,
+		buf:      make([]byte, binary.MaxVarintLen64), // Also sufficient for uint64.
 	}, nil
 }
 
@@ -232,6 +238,38 @@ func (p *diskPersistence) indexPath() string {
 	return path.Join(p.basePath, indexFileName)
 }
 
+// PersistIndexes persists the indexes to disk. Do not call it concurrently with
+// LoadIndexes as they share a buffer for staging. This method depends on the
+// following type conversions being possible:
+//     clientmodel.LabelName -> string
+//     clientmodel.LabelValue -> string
+//     clientmodel.Fingerprint -> uint64
+//
+// Description of the on-disk format:
+//
+// Label names and label values are encoded as their varint-encoded length
+// followed by their byte sequence.
+//
+// Fingerprints are encoded as big-endian uint64.
+//
+// The file starts with the 'magic' byte sequence "PrometheusIndexes", followed
+// by a varint-encoded version number (currently 1).
+//
+// The indexes follow one after another in the order FingerprintToSeries,
+// LabelPairToFingerprints, LabelNameToLabelValues. Each index starts with the
+// varint-encoded number of entries in that index, followed by the corresponding
+// number of entries.
+//
+// An entry in FingerprintToSeries consists of a fingerprint, followed by the
+// number of label pairs, followed by those label pairs, each in order label
+// name and then label value.
+//
+// An entry in LabelPairToFingerprints consists of a label name, then a label
+// value, then a varint-encoded number of fingerprints, followed by those
+// fingerprints.
+//
+// An entry in LabelNameToLabelValues consists of a label name, followed by the
+// varint-encoded number of label values, followed by those label values.
 func (p *diskPersistence) PersistIndexes(i *Indexes) error {
 	f, err := os.OpenFile(p.indexPath(), os.O_WRONLY|os.O_TRUNC|os.O_CREATE, 0640)
 	if err != nil {
@@ -239,21 +277,132 @@ func (p *diskPersistence) PersistIndexes(i *Indexes) error {
 	}
 	defer f.Close()
 
-	enc := gob.NewEncoder(f)
-	if err := enc.Encode(i); err != nil {
+	p.setBufLen(binary.MaxVarintLen64)
+
+	w := bufio.NewWriterSize(f, indexBufSize)
+	if _, err := w.WriteString(indexMagicString); err != nil {
+		return err
+	}
+	if err := p.persistVarint(w, indexFormatVersion); err != nil {
 		return err
 	}
 
+	if err := p.persistFingerprintToSeries(w, i.FingerprintToSeries); err != nil {
+		return err
+	}
+	if err := p.persistLabelPairToFingerprints(w, i.LabelPairToFingerprints); err != nil {
+		return err
+	}
+	if err := p.persistLabelNameToLabelValues(w, i.LabelNameToLabelValues); err != nil {
+		return err
+	}
+
+	return w.Flush()
+}
+
+func (p *diskPersistence) persistVarint(w io.Writer, i int) error {
+	bytesWritten := binary.PutVarint(p.buf, int64(i))
+	_, err := w.Write(p.buf[:bytesWritten])
+	return err
+}
+
+// persistFingerprint depends on clientmodel.Fingerprint to be convertible to
+// uint64.
+func (p *diskPersistence) persistFingerprint(w io.Writer, fp clientmodel.Fingerprint) error {
+	binary.BigEndian.PutUint64(p.buf, uint64(fp))
+	_, err := w.Write(p.buf[:8])
+	return err
+}
+
+func (p *diskPersistence) persistString(w *bufio.Writer, s string) error {
+	if err := p.persistVarint(w, len(s)); err != nil {
+		return err
+	}
+	_, err := w.WriteString(s)
+	return err
+}
+
+// persistFingerprintToSeries depends on clientmodel.LabelName and
+// clientmodel.LabelValue to be convertible to string.
+func (p *diskPersistence) persistFingerprintToSeries(w *bufio.Writer, index map[clientmodel.Fingerprint]*memorySeries) error {
+	if err := p.persistVarint(w, len(index)); err != nil {
+		return err
+	}
+	for fp, ms := range index {
+		if err := p.persistFingerprint(w, fp); err != nil {
+			return err
+		}
+		if err := p.persistVarint(w, len(ms.metric)); err != nil {
+			return err
+		}
+		for n, v := range ms.metric {
+			if err := p.persistString(w, string(n)); err != nil {
+				return err
+			}
+			if err := p.persistString(w, string(v)); err != nil {
+				return err
+			}
+		}
+	}
 	return nil
 }
 
+// persistLabelPairToFingerprints depends on clientmodel.LabelName and
+// clientmodel.LabelValue to be convertible to string.
+func (p *diskPersistence) persistLabelPairToFingerprints(w *bufio.Writer, index map[metric.LabelPair]utility.Set) error {
+	if err := p.persistVarint(w, len(index)); err != nil {
+		return err
+	}
+	for lp, fps := range index {
+		if err := p.persistString(w, string(lp.Name)); err != nil {
+			return err
+		}
+		if err := p.persistString(w, string(lp.Value)); err != nil {
+			return err
+		}
+		if err := p.persistVarint(w, len(fps)); err != nil {
+			return err
+		}
+		for fp := range fps {
+			if err := p.persistFingerprint(w, fp.(clientmodel.Fingerprint)); err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
+// persistLabelNameToLabelValues depends on clientmodel.LabelValue to be convertible to string.
+func (p *diskPersistence) persistLabelNameToLabelValues(w *bufio.Writer, index map[clientmodel.LabelName]utility.Set) error {
+	if err := p.persistVarint(w, len(index)); err != nil {
+		return err
+	}
+	for ln, lvs := range index {
+		if err := p.persistString(w, string(ln)); err != nil {
+			return err
+		}
+		if err := p.persistVarint(w, len(lvs)); err != nil {
+			return err
+		}
+		for lv := range lvs {
+			if err := p.persistString(w, string(lv.(clientmodel.LabelValue))); err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
+// LoadIndexes loads the indexes from disk. See PersistIndexes for details about
+// the disk format. Do not call LoadIndexes and PersistIndexes concurrently as
+// they share a buffer for staging.
 func (p *diskPersistence) LoadIndexes() (*Indexes, error) {
 	f, err := os.Open(p.indexPath())
 	if os.IsNotExist(err) {
 		return &Indexes{
-			FingerprintToSeries:     make(map[clientmodel.Fingerprint]*memorySeries),
-			LabelPairToFingerprints: make(map[metric.LabelPair]utility.Set),
-			LabelNameToLabelValues:  make(map[clientmodel.LabelName]utility.Set),
+			FingerprintToSeries:     map[clientmodel.Fingerprint]*memorySeries{},
+			LabelPairToFingerprints: map[metric.LabelPair]utility.Set{},
+			LabelNameToLabelValues:  map[clientmodel.LabelName]utility.Set{},
 		}, nil
 	}
 	if err != nil {
@@ -261,13 +410,162 @@ func (p *diskPersistence) LoadIndexes() (*Indexes, error) {
 	}
 	defer f.Close()
 
-	dec := gob.NewDecoder(f)
-	var i Indexes
-	if err := dec.Decode(&i); err != nil {
+	r := bufio.NewReaderSize(f, indexBufSize)
+
+	p.setBufLen(len(indexMagicString))
+	if _, err := io.ReadFull(r, p.buf); err != nil {
+		return nil, err
+	}
+	magic := string(p.buf)
+	if magic != indexMagicString {
+		return nil, fmt.Errorf(
+			"unexpected magic string, want %q, got %q",
+			indexMagicString, magic,
+		)
+	}
+	if version, err := binary.ReadVarint(r); version != indexFormatVersion || err != nil {
+		return nil, fmt.Errorf("unknown index format version, want %d", indexFormatVersion)
+	}
+
+	i := &Indexes{}
+
+	if err := p.loadFingerprintToSeries(r, i); err != nil {
+		return nil, err
+	}
+	if err := p.loadLabelPairToFingerprints(r, i); err != nil {
+		return nil, err
+	}
+	if err := p.loadLabelNameToLabelValues(r, i); err != nil {
 		return nil, err
 	}
 
-	return &i, nil
+	return i, nil
+}
+
+func (p *diskPersistence) loadFingerprintToSeries(r *bufio.Reader, i *Indexes) error {
+	length, err := binary.ReadVarint(r)
+	if err != nil {
+		return err
+	}
+	i.FingerprintToSeries = make(map[clientmodel.Fingerprint]*memorySeries, length)
+
+	for ; length > 0; length-- {
+		fp, err := p.loadFingerprint(r)
+		if err != nil {
+			return err
+		}
+		numLabelPairs, err := binary.ReadVarint(r)
+		if err != nil {
+			return err
+		}
+		m := make(clientmodel.Metric, numLabelPairs)
+		i.FingerprintToSeries[fp] = &memorySeries{metric: m}
+		for ; numLabelPairs > 0; numLabelPairs-- {
+			ln, err := p.loadString(r)
+			if err != nil {
+				return err
+			}
+			lv, err := p.loadString(r)
+			if err != nil {
+				return err
+			}
+			m[clientmodel.LabelName(ln)] = clientmodel.LabelValue(lv)
+		}
+	}
+	return nil
+}
+
+func (p *diskPersistence) loadLabelPairToFingerprints(r *bufio.Reader, i *Indexes) error {
+	length, err := binary.ReadVarint(r)
+	if err != nil {
+		return err
+	}
+	i.LabelPairToFingerprints = make(map[metric.LabelPair]utility.Set, length)
+
+	for ; length > 0; length-- {
+		ln, err := p.loadString(r)
+		if err != nil {
+			return err
+		}
+		lv, err := p.loadString(r)
+		if err != nil {
+			return err
+		}
+		numFPs, err := binary.ReadVarint(r)
+		if err != nil {
+			return err
+		}
+		s := make(utility.Set, numFPs)
+		i.LabelPairToFingerprints[metric.LabelPair{
+			Name:  clientmodel.LabelName(ln),
+			Value: clientmodel.LabelValue(lv),
+		}] = s
+		for ; numFPs > 0; numFPs-- {
+			fp, err := p.loadFingerprint(r)
+			if err != nil {
+				return err
+			}
+			s.Add(fp)
+		}
+	}
+	return nil
+}
+
+func (p *diskPersistence) loadLabelNameToLabelValues(r *bufio.Reader, i *Indexes) error {
+	length, err := binary.ReadVarint(r)
+	if err != nil {
+		return err
+	}
+	i.LabelNameToLabelValues = make(map[clientmodel.LabelName]utility.Set, length)
+
+	for ; length > 0; length-- {
+		ln, err := p.loadString(r)
+		if err != nil {
+			return err
+		}
+		numLVs, err := binary.ReadVarint(r)
+		if err != nil {
+			return err
+		}
+		s := make(utility.Set, numLVs)
+		i.LabelNameToLabelValues[clientmodel.LabelName(ln)] = s
+		for ; numLVs > 0; numLVs-- {
+			lv, err := p.loadString(r)
+			if err != nil {
+				return err
+			}
+			s.Add(clientmodel.LabelValue(lv))
+		}
+	}
+	return nil
+}
+
+func (p *diskPersistence) loadFingerprint(r io.Reader) (clientmodel.Fingerprint, error) {
+	p.setBufLen(8)
+	if _, err := io.ReadFull(r, p.buf); err != nil {
+		return 0, err
+	}
+	return clientmodel.Fingerprint(binary.BigEndian.Uint64(p.buf)), nil
+}
+
+func (p *diskPersistence) loadString(r *bufio.Reader) (string, error) {
+	length, err := binary.ReadVarint(r)
+	if err != nil {
+		return "", err
+	}
+	p.setBufLen(int(length))
+	if _, err := io.ReadFull(r, p.buf); err != nil {
+		return "", err
+	}
+	return string(p.buf), nil
+}
+
+func (p *diskPersistence) setBufLen(l int) {
+	if cap(p.buf) >= l {
+		p.buf = p.buf[:l]
+	} else {
+		p.buf = make([]byte, l)
+	}
 }
 
 func (p *diskPersistence) headsPath() string {

storage/local/persistence_test.go

@@ -2,6 +2,7 @@ package storage_ng
 
 import (
 	"io/ioutil"
+	"os"
 	"testing"
 
 	clientmodel "github.com/prometheus/client_golang/model"
@@ -10,8 +11,8 @@ import (
 	"github.com/prometheus/prometheus/utility"
 )
 
-func TestIndexPersistence(t *testing.T) {
-	expected := Indexes{
+var (
+	indexes = Indexes{
 		FingerprintToSeries: map[clientmodel.Fingerprint]*memorySeries{
 			0: {
 				metric: clientmodel.Metric{
@@ -23,6 +24,13 @@ func TestIndexPersistence(t *testing.T) {
 				metric: clientmodel.Metric{
 					clientmodel.MetricNameLabel: "metric_0",
 					"label_2":                   "value_2",
+					"label_3":                   "value_3",
+				},
+			},
+			2: {
+				metric: clientmodel.Metric{
+					clientmodel.MetricNameLabel: "metric_1",
+					"label_1":                   "value_2",
 				},
 			},
 		},
@@ -31,77 +39,150 @@ func TestIndexPersistence(t *testing.T) {
 				Name:  clientmodel.MetricNameLabel,
 				Value: "metric_0",
 			}: {
-				0: struct{}{},
-				1: struct{}{},
+				clientmodel.Fingerprint(0): struct{}{},
+				clientmodel.Fingerprint(1): struct{}{},
+			},
+			metric.LabelPair{
+				Name:  clientmodel.MetricNameLabel,
+				Value: "metric_1",
+			}: {
+				clientmodel.Fingerprint(2): struct{}{},
 			},
 			metric.LabelPair{
 				Name:  "label_1",
 				Value: "value_1",
 			}: {
-				0: struct{}{},
+				clientmodel.Fingerprint(0): struct{}{},
+			},
+			metric.LabelPair{
+				Name:  "label_1",
+				Value: "value_2",
+			}: {
+				clientmodel.Fingerprint(2): struct{}{},
 			},
 			metric.LabelPair{
 				Name:  "label_2",
 				Value: "value_2",
 			}: {
-				1: struct{}{},
+				clientmodel.Fingerprint(1): struct{}{},
+			},
+			metric.LabelPair{
+				Name:  "label_3",
+				Value: "value_2",
+			}: {
+				clientmodel.Fingerprint(1): struct{}{},
 			},
 		},
 		LabelNameToLabelValues: map[clientmodel.LabelName]utility.Set{
 			clientmodel.MetricNameLabel: {
 				clientmodel.LabelValue("metric_0"): struct{}{},
+				clientmodel.LabelValue("metric_1"): struct{}{},
 			},
 			"label_1": {
 				clientmodel.LabelValue("value_1"): struct{}{},
+				clientmodel.LabelValue("value_2"): struct{}{},
 			},
 			"label_2": {
 				clientmodel.LabelValue("value_2"): struct{}{},
 			},
+			"label_3": {
+				clientmodel.LabelValue("value_3"): struct{}{},
+			},
 		},
 	}
+)
 
+func TestIndexPersistence(t *testing.T) {
 	basePath, err := ioutil.TempDir("", "test_index_persistence")
 	if err != nil {
 		t.Fatal(err)
 	}
+	defer os.RemoveAll(basePath)
 	p, err := NewDiskPersistence(basePath, 1024)
 	if err != nil {
 		t.Fatal(err)
 	}
-	p.PersistIndexes(&expected)
+
+	if err := p.PersistIndexes(&indexes); err != nil {
+		t.Fatal(err)
+	}
 
 	actual, err := p.LoadIndexes()
 	if err != nil {
 		t.Fatal(err)
 	}
 
-	if len(actual.FingerprintToSeries) != len(expected.FingerprintToSeries) {
-		t.Fatalf("Count mismatch: Got %d; want %d", len(actual.FingerprintToSeries), len(expected.FingerprintToSeries))
+	if len(actual.FingerprintToSeries) != len(indexes.FingerprintToSeries) {
+		t.Fatalf("Count mismatch: Got %d; want %d", len(actual.FingerprintToSeries), len(indexes.FingerprintToSeries))
 	}
 	for fp, actualSeries := range actual.FingerprintToSeries {
-		expectedSeries := expected.FingerprintToSeries[fp]
+		expectedSeries := indexes.FingerprintToSeries[fp]
 		if !expectedSeries.metric.Equal(actualSeries.metric) {
 			t.Fatalf("%s: Got %s; want %s", fp, actualSeries.metric, expectedSeries.metric)
 		}
 	}
 
-	if len(actual.LabelPairToFingerprints) != len(expected.LabelPairToFingerprints) {
-		t.Fatalf("Count mismatch: Got %d; want %d", len(actual.LabelPairToFingerprints), len(expected.LabelPairToFingerprints))
+	if len(actual.LabelPairToFingerprints) != len(indexes.LabelPairToFingerprints) {
+		t.Fatalf("Count mismatch: Got %d; want %d", len(actual.LabelPairToFingerprints), len(indexes.LabelPairToFingerprints))
 	}
 	for lp, actualFps := range actual.LabelPairToFingerprints {
-		expectedFps := expected.LabelPairToFingerprints[lp]
+		expectedFps := indexes.LabelPairToFingerprints[lp]
 		if len(actualFps) != len(actualFps.Intersection(expectedFps)) {
 			t.Fatalf("%s: Got %s; want %s", lp, actualFps, expectedFps)
 		}
 	}
 
-	if len(actual.LabelNameToLabelValues) != len(expected.LabelNameToLabelValues) {
-		t.Fatalf("Count mismatch: Got %d; want %d", len(actual.LabelNameToLabelValues), len(expected.LabelNameToLabelValues))
+	if len(actual.LabelNameToLabelValues) != len(indexes.LabelNameToLabelValues) {
+		t.Fatalf("Count mismatch: Got %d; want %d", len(actual.LabelNameToLabelValues), len(indexes.LabelNameToLabelValues))
 	}
 	for name, actualVals := range actual.LabelNameToLabelValues {
-		expectedVals := expected.LabelNameToLabelValues[name]
+		expectedVals := indexes.LabelNameToLabelValues[name]
 		if len(actualVals) != len(actualVals.Intersection(expectedVals)) {
 			t.Fatalf("%s: Got %s; want %s", name, actualVals, expectedVals)
 		}
 	}
 }
+
+func BenchmarkPersistIndexes(b *testing.B) {
+	basePath, err := ioutil.TempDir("", "test_index_persistence")
+	if err != nil {
+		b.Fatal(err)
+	}
+	defer os.RemoveAll(basePath)
+	p, err := NewDiskPersistence(basePath, 1024)
+	if err != nil {
+		b.Fatal(err)
+	}
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		if err := p.PersistIndexes(&indexes); err != nil {
+			b.Fatal(err)
+		}
+	}
+	b.StopTimer()
+}
+
+func BenchmarkLoadIndexes(b *testing.B) {
+	basePath, err := ioutil.TempDir("", "test_index_persistence")
+	if err != nil {
+		b.Fatal(err)
+	}
+	defer os.RemoveAll(basePath)
+	p, err := NewDiskPersistence(basePath, 1024)
+	if err != nil {
+		b.Fatal(err)
+	}
+	if err := p.PersistIndexes(&indexes); err != nil {
+		b.Fatal(err)
+	}
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_, err := p.LoadIndexes()
+		if err != nil {
+			b.Fatal(err)
+		}
+	}
+	b.StopTimer()
+}

storage/local/series.go

@@ -1,8 +1,6 @@
 package storage_ng
 
 import (
-	"bytes"
-	"encoding/gob"
 	"sort"
 	"sync"
 
@@ -355,30 +353,6 @@ func (s *memorySeries) values() metric.Values {
 	return values
 }
 
-var gobWriter bytes.Buffer
-var seriesEncoder *gob.Encoder
-
-func (s *memorySeries) GobEncode() ([]byte, error) {
-	gobWriter.Reset()
-	if seriesEncoder == nil {
-		seriesEncoder = gob.NewEncoder(&gobWriter)
-	}
-	err := seriesEncoder.Encode(s.metric)
-	return gobWriter.Bytes(), err
-}
-
-var gobReader bytes.Reader
-var seriesDecoder *gob.Decoder
-
-func (s *memorySeries) GobDecode(buf []byte) error {
-	gobReader = *bytes.NewReader(buf)
-	if seriesDecoder == nil {
-		seriesDecoder = gob.NewDecoder(&gobReader)
-	}
-	err := seriesDecoder.Decode(&s.metric)
-	return err
-}
-
 func (it *memorySeriesIterator) GetValueAtTime(t clientmodel.Timestamp) metric.Values {
 	it.mtx.Lock()
 	defer it.mtx.Unlock()
@@ -419,12 +393,11 @@ func (it *memorySeriesIterator) GetValueAtTime(t clientmodel.Timestamp) metric.V
 			it.chunks[i-1].newIterator().getValueAtTime(t)[0],
 			it.chunks[i].newIterator().getValueAtTime(t)[0],
 		}
-	} else {
-		// We ended up in the middle of a chunk. We might stay there for a while,
-		// so save it as the current chunk iterator.
-		it.chunkIt = it.chunks[i].newIterator()
-		return it.chunkIt.getValueAtTime(t)
 	}
+	// We ended up in the middle of a chunk. We might stay there for a while,
+	// so save it as the current chunk iterator.
+	it.chunkIt = it.chunks[i].newIterator()
+	return it.chunkIt.getValueAtTime(t)
 }
 
 func (it *memorySeriesIterator) GetBoundaryValues(in metric.Interval) metric.Values {

storage/local/storage.go

@@ -282,7 +282,7 @@ func (s *memorySeriesStorage) purgePeriodically(stop <-chan bool) {
 			glog.Info("Purging old series data...")
 			s.mtx.RLock()
 			fps := make([]clientmodel.Fingerprint, 0, len(s.fingerprintToSeries))
-			for fp, _ := range s.fingerprintToSeries {
+			for fp := range s.fingerprintToSeries {
 				fps = append(fps, fp)
 			}
 			s.mtx.RUnlock()