func TestCheckpointAndLoadFPMappings(t *testing.T) {
	p, closer := newTestPersistence(t, 1)
	defer closer.Close()

	in := fpMappings{
		1: map[string]model.Fingerprint{
			"foo": 1,
			"bar": 2,
		},
		3: map[string]model.Fingerprint{
			"baz": 4,
		},
	}

	if err := p.checkpointFPMappings(in); err != nil {
		t.Fatal(err)
	}

	out, fp, err := p.loadFPMappings()
	if err != nil {
		t.Fatal(err)
	}
	if got, want := fp, model.Fingerprint(4); got != want {
		t.Errorf("got highest FP %v, want %v", got, want)
	}
	if !reflect.DeepEqual(in, out) {
		t.Errorf("got collision map %v, want %v", out, in)
	}
}

// Get implements the Notifies interface.
func (n *Notifies) Get(dest string, fps ...model.Fingerprint) ([]*types.NotifyInfo, error) {
	var result []*types.NotifyInfo

	for _, fp := range fps {
		row := n.db.QueryRow(`
			SELECT alert, receiver, resolved, timestamp
			FROM notify_info
			WHERE receiver == $1 AND alert == $2
		`, dest, int64(fp))

		var alertFP int64

		var ni types.NotifyInfo
		err := row.Scan(
			&alertFP,
			&ni.Receiver,
			&ni.Resolved,
			&ni.Timestamp,
		)
		if err == sql.ErrNoRows {
			result = append(result, nil)
			continue
		}
		if err != nil {
			return nil, err
		}

		ni.Alert = model.Fingerprint(alertFP)

		result = append(result, &ni)
	}

	return result, nil
}

func (p *persistence) rebuildLabelIndexes(
	fpToSeries map[model.Fingerprint]*memorySeries,
) error {
	count := 0
	log.Info("Rebuilding label indexes.")
	log.Info("Indexing metrics in memory.")
	for fp, s := range fpToSeries {
		p.indexMetric(fp, s.metric)
		count++
		if count%10000 == 0 {
			log.Infof("%d metrics queued for indexing.", count)
		}
	}
	log.Info("Indexing archived metrics.")
	var fp codable.Fingerprint
	var m codable.Metric
	if err := p.archivedFingerprintToMetrics.ForEach(func(kv index.KeyValueAccessor) error {
		if err := kv.Key(&fp); err != nil {
			return err
		}
		if err := kv.Value(&m); err != nil {
			return err
		}
		p.indexMetric(model.Fingerprint(fp), model.Metric(m))
		count++
		if count%10000 == 0 {
			log.Infof("%d metrics queued for indexing.", count)
		}
		return nil
	}); err != nil {
		return err
	}
	log.Info("All requests for rebuilding the label indexes queued. (Actual processing may lag behind.)")
	return nil
}

func (m *fpMapper) nextMappedFP() model.Fingerprint {
	mappedFP := model.Fingerprint(atomic.AddUint64((*uint64)(&m.highestMappedFP), 1))
	if mappedFP > maxMappedFP {
		panic(fmt.Errorf("more than %v fingerprints mapped in collision detection", maxMappedFP))
	}
	return mappedFP
}

// Fingerprint returns a quasi-unique fingerprint for the NotifyInfo.
func (n *NotifyInfo) Fingerprint() model.Fingerprint {
	h := fnv.New64a()
	h.Write([]byte(n.Receiver))

	fp := model.Fingerprint(h.Sum64())

	return fp ^ n.Alert
}

func BenchmarkFingerprintLockerSerial(b *testing.B) {
	numFingerprints := 10
	locker := newFingerprintLocker(100)

	b.ResetTimer()
	for i := 0; i < b.N; i++ {
		fp := model.Fingerprint(i % numFingerprints)
		locker.Lock(fp)
		locker.Unlock(fp)
	}
}

// UnmarshalBinary implements encoding.BinaryUnmarshaler.
func (fps *Fingerprints) UnmarshalBinary(buf []byte) error {
	numFPs, offset := binary.Varint(buf)
	if offset <= 0 {
		return fmt.Errorf("could not decode length of Fingerprints, varint decoding returned %d", offset)
	}
	*fps = make(Fingerprints, numFPs)

	for i := range *fps {
		(*fps)[i] = model.Fingerprint(binary.BigEndian.Uint64(buf[offset+i*8:]))
	}
	return nil
}

func BenchmarkFingerprintLockerParallel(b *testing.B) {
	numGoroutines := 10
	numFingerprints := 10
	numLockOps := b.N
	locker := newFingerprintLocker(100)

	wg := sync.WaitGroup{}
	b.ResetTimer()
	for i := 0; i < numGoroutines; i++ {
		wg.Add(1)
		go func(i int) {
			for j := 0; j < numLockOps; j++ {
				fp1 := model.Fingerprint(j % numFingerprints)
				fp2 := model.Fingerprint(j%numFingerprints + numFingerprints)
				locker.Lock(fp1)
				locker.Lock(fp2)
				locker.Unlock(fp2)
				locker.Unlock(fp1)
			}
			wg.Done()
		}(i)
	}
	wg.Wait()
}

// fingerprintsModifiedBefore returns the fingerprints of archived timeseries
// that have live samples before the provided timestamp. This method is
// goroutine-safe.
func (p *persistence) fingerprintsModifiedBefore(beforeTime model.Time) ([]model.Fingerprint, error) {
	var fp codable.Fingerprint
	var tr codable.TimeRange
	fps := []model.Fingerprint{}
	err := p.archivedFingerprintToTimeRange.ForEach(func(kv index.KeyValueAccessor) error {
		if err := kv.Value(&tr); err != nil {
			return err
		}
		if tr.First.Before(beforeTime) {
			if err := kv.Key(&fp); err != nil {
				return err
			}
			fps = append(fps, model.Fingerprint(fp))
		}
		return nil
	})
	return fps, err
}

func (ag *aggrGroup) run(nf notifyFunc) {
	ag.done = make(chan struct{})

	defer close(ag.done)
	defer ag.next.Stop()

	for {
		select {
		case now := <-ag.next.C:
			// Give the notifcations time until the next flush to
			// finish before terminating them.
			ctx, cancel := context.WithTimeout(ag.ctx, ag.timeout(ag.opts.GroupInterval))

			// The now time we retrieve from the ticker is the only reliable
			// point of time reference for the subsequent notification pipeline.
			// Calculating the current time directly is prone to flaky behavior,
			// which usually only becomes apparent in tests.
			ctx = notify.WithNow(ctx, now)

			// Populate context with information needed along the pipeline.
			ctx = notify.WithGroupKey(ctx, model.Fingerprint(ag.GroupKey()))
			ctx = notify.WithGroupLabels(ctx, ag.labels)
			ctx = notify.WithReceiverName(ctx, ag.opts.Receiver)
			ctx = notify.WithRepeatInterval(ctx, ag.opts.RepeatInterval)

			// Wait the configured interval before calling flush again.
			ag.mtx.Lock()
			ag.next.Reset(ag.opts.GroupInterval)
			ag.mtx.Unlock()

			ag.flush(func(alerts ...*types.Alert) bool {
				return nf(ctx, alerts...)
			})

			cancel()

		case <-ag.ctx.Done():
			return
		}
	}
}

// loadFPMappings loads the fingerprint mappings. It also returns the highest
// mapped fingerprint and any error encountered. If p.mappingsFileName is not
// found, the method returns (fpMappings{}, 0, nil). Do not call concurrently
// with checkpointFPMappings.
func (p *persistence) loadFPMappings() (fpMappings, model.Fingerprint, error) {
	fpm := fpMappings{}
	var highestMappedFP model.Fingerprint

	f, err := os.Open(p.mappingsFileName())
	if os.IsNotExist(err) {
		return fpm, 0, nil
	}
	if err != nil {
		return nil, 0, err
	}
	defer f.Close()
	r := bufio.NewReaderSize(f, fileBufSize)

	buf := make([]byte, len(mappingsMagicString))
	if _, err := io.ReadFull(r, buf); err != nil {
		return nil, 0, err
	}
	magic := string(buf)
	if magic != mappingsMagicString {
		return nil, 0, fmt.Errorf(
			"unexpected magic string, want %q, got %q",
			mappingsMagicString, magic,
		)
	}
	version, err := binary.ReadUvarint(r)
	if version != mappingsFormatVersion || err != nil {
		return nil, 0, fmt.Errorf("unknown fingerprint mappings format version, want %d", mappingsFormatVersion)
	}
	numRawFPs, err := binary.ReadUvarint(r)
	if err != nil {
		return nil, 0, err
	}
	for ; numRawFPs > 0; numRawFPs-- {
		rawFP, err := codable.DecodeUint64(r)
		if err != nil {
			return nil, 0, err
		}
		numMappings, err := binary.ReadUvarint(r)
		if err != nil {
			return nil, 0, err
		}
		mappings := make(map[string]model.Fingerprint, numMappings)
		for ; numMappings > 0; numMappings-- {
			lenMS, err := binary.ReadUvarint(r)
			if err != nil {
				return nil, 0, err
			}
			buf := make([]byte, lenMS)
			if _, err := io.ReadFull(r, buf); err != nil {
				return nil, 0, err
			}
			fp, err := codable.DecodeUint64(r)
			if err != nil {
				return nil, 0, err
			}
			mappedFP := model.Fingerprint(fp)
			if mappedFP > highestMappedFP {
				highestMappedFP = mappedFP
			}
			mappings[string(buf)] = mappedFP
		}
		fpm[model.Fingerprint(rawFP)] = mappings
	}
	return fpm, highestMappedFP, nil
}

func TestFPMapper(t *testing.T) {
	sm := newSeriesMap()

	p, closer := newTestPersistence(t, 1)
	defer closer.Close()

	mapper, err := newFPMapper(sm, p)
	if err != nil {
		t.Fatal(err)
	}

	// Everything is empty, resolving a FP should do nothing.
	gotFP, err := mapper.mapFP(fp1, cm11)
	if err != nil {
		t.Fatal(err)
	}
	if wantFP := fp1; gotFP != wantFP {
		t.Errorf("got fingerprint %v, want fingerprint %v", gotFP, wantFP)
	}
	gotFP, err = mapper.mapFP(fp1, cm12)
	if err != nil {
		t.Fatal(err)
	}
	if wantFP := fp1; gotFP != wantFP {
		t.Errorf("got fingerprint %v, want fingerprint %v", gotFP, wantFP)
	}

	// cm11 is in sm. Adding cm11 should do nothing. Mapping cm12 should resolve
	// the collision.
	sm.put(fp1, &memorySeries{metric: cm11})
	gotFP, err = mapper.mapFP(fp1, cm11)
	if err != nil {
		t.Fatal(err)
	}
	if wantFP := fp1; gotFP != wantFP {
		t.Errorf("got fingerprint %v, want fingerprint %v", gotFP, wantFP)
	}
	gotFP, err = mapper.mapFP(fp1, cm12)
	if err != nil {
		t.Fatal(err)
	}
	if wantFP := model.Fingerprint(1); gotFP != wantFP {
		t.Errorf("got fingerprint %v, want fingerprint %v", gotFP, wantFP)
	}

	// The mapped cm12 is added to sm, too. That should not change the outcome.
	sm.put(model.Fingerprint(1), &memorySeries{metric: cm12})
	gotFP, err = mapper.mapFP(fp1, cm11)
	if err != nil {
		t.Fatal(err)
	}
	if wantFP := fp1; gotFP != wantFP {
		t.Errorf("got fingerprint %v, want fingerprint %v", gotFP, wantFP)
	}
	gotFP, err = mapper.mapFP(fp1, cm12)
	if err != nil {
		t.Fatal(err)
	}
	if wantFP := model.Fingerprint(1); gotFP != wantFP {
		t.Errorf("got fingerprint %v, want fingerprint %v", gotFP, wantFP)
	}

	// Now map cm13, should reproducibly result in the next mapped FP.
	gotFP, err = mapper.mapFP(fp1, cm13)
	if err != nil {
		t.Fatal(err)
	}
	if wantFP := model.Fingerprint(2); gotFP != wantFP {
		t.Errorf("got fingerprint %v, want fingerprint %v", gotFP, wantFP)
	}
	gotFP, err = mapper.mapFP(fp1, cm13)
	if err != nil {
		t.Fatal(err)
	}
	if wantFP := model.Fingerprint(2); gotFP != wantFP {
		t.Errorf("got fingerprint %v, want fingerprint %v", gotFP, wantFP)
	}

	// Add cm13 to sm. Should not change anything.
	sm.put(model.Fingerprint(2), &memorySeries{metric: cm13})
	gotFP, err = mapper.mapFP(fp1, cm11)
	if err != nil {
		t.Fatal(err)
	}
	if wantFP := fp1; gotFP != wantFP {
		t.Errorf("got fingerprint %v, want fingerprint %v", gotFP, wantFP)
	}
	gotFP, err = mapper.mapFP(fp1, cm12)
	if err != nil {
		t.Fatal(err)
	}
	if wantFP := model.Fingerprint(1); gotFP != wantFP {
		t.Errorf("got fingerprint %v, want fingerprint %v", gotFP, wantFP)
	}
	gotFP, err = mapper.mapFP(fp1, cm13)
	if err != nil {
		t.Fatal(err)
	}
	if wantFP := model.Fingerprint(2); gotFP != wantFP {
		t.Errorf("got fingerprint %v, want fingerprint %v", gotFP, wantFP)
//.........这里部分代码省略.........

package local

import (
	"testing"

	"github.com/prometheus/common/model"
)

var (
	// cm11, cm12, cm13 are colliding with fp1.
	// cm21, cm22 are colliding with fp2.
	// cm31, cm32 are colliding with fp3, which is below maxMappedFP.
	// Note that fingerprints are set and not actually calculated.
	// The collision detection is independent from the actually used
	// fingerprinting algorithm.
	fp1  = model.Fingerprint(maxMappedFP + 1)
	fp2  = model.Fingerprint(maxMappedFP + 2)
	fp3  = model.Fingerprint(1)
	cm11 = model.Metric{
		"foo":   "bar",
		"dings": "bumms",
	}
	cm12 = model.Metric{
		"bar": "foo",
	}
	cm13 = model.Metric{
		"foo": "bar",
	}
	cm21 = model.Metric{
		"foo":   "bumms",
		"dings": "bar",

// scan works like bufio.Scanner.Scan.
func (hs *headsScanner) scan() bool {
	if hs.seriesCurrent == hs.seriesTotal || hs.err != nil {
		return false
	}

	var (
		seriesFlags      byte
		fpAsInt          uint64
		metric           codable.Metric
		persistWatermark int64
		modTimeNano      int64
		modTime          time.Time
		chunkDescsOffset int64
		savedFirstTime   int64
		numChunkDescs    int64
		firstTime        int64
		lastTime         int64
		encoding         byte
		ch               chunk.Chunk
		lastTimeHead     model.Time
	)
	if seriesFlags, hs.err = hs.r.ReadByte(); hs.err != nil {
		return false
	}
	headChunkPersisted := seriesFlags&flagHeadChunkPersisted != 0
	if fpAsInt, hs.err = codable.DecodeUint64(hs.r); hs.err != nil {
		return false
	}
	hs.fp = model.Fingerprint(fpAsInt)

	if hs.err = metric.UnmarshalFromReader(hs.r); hs.err != nil {
		return false
	}
	if hs.version != headsFormatLegacyVersion {
		// persistWatermark only present in v2.
		persistWatermark, hs.err = binary.ReadVarint(hs.r)
		if hs.err != nil {
			return false
		}
		modTimeNano, hs.err = binary.ReadVarint(hs.r)
		if hs.err != nil {
			return false
		}
		if modTimeNano != -1 {
			modTime = time.Unix(0, modTimeNano)
		}
	}
	if chunkDescsOffset, hs.err = binary.ReadVarint(hs.r); hs.err != nil {
		return false
	}
	if savedFirstTime, hs.err = binary.ReadVarint(hs.r); hs.err != nil {
		return false
	}

	if numChunkDescs, hs.err = binary.ReadVarint(hs.r); hs.err != nil {
		return false
	}
	chunkDescs := make([]*chunk.Desc, numChunkDescs)
	if hs.version == headsFormatLegacyVersion {
		if headChunkPersisted {
			persistWatermark = numChunkDescs
		} else {
			persistWatermark = numChunkDescs - 1
		}
	}
	headChunkClosed := true // Initial assumption.
	for i := int64(0); i < numChunkDescs; i++ {
		if i < persistWatermark {
			if firstTime, hs.err = binary.ReadVarint(hs.r); hs.err != nil {
				return false
			}
			if lastTime, hs.err = binary.ReadVarint(hs.r); hs.err != nil {
				return false
			}
			chunkDescs[i] = &chunk.Desc{
				ChunkFirstTime: model.Time(firstTime),
				ChunkLastTime:  model.Time(lastTime),
			}
			chunk.NumMemDescs.Inc()
		} else {
			// Non-persisted chunk.
			// If there are non-persisted chunks at all, we consider
			// the head chunk not to be closed yet.
			headChunkClosed = false
			if encoding, hs.err = hs.r.ReadByte(); hs.err != nil {
				return false
			}
			if ch, hs.err = chunk.NewForEncoding(chunk.Encoding(encoding)); hs.err != nil {
				return false
			}
			if hs.err = ch.Unmarshal(hs.r); hs.err != nil {
				return false
			}
			cd := chunk.NewDesc(ch, ch.FirstTime())
			if i < numChunkDescs-1 {
				// This is NOT the head chunk. So it's a chunk
				// to be persisted, and we need to populate lastTime.
				hs.chunksToPersistTotal++
				cd.MaybePopulateLastTime()
//.........这里部分代码省略.........

	chunkHeaderLen             = 17
	chunkHeaderTypeOffset      = 0
	chunkHeaderFirstTimeOffset = 1
	chunkHeaderLastTimeOffset  = 9
	chunkLenWithHeader         = chunkLen + chunkHeaderLen
	chunkMaxBatchSize          = 62 // Max no. of chunks to load or write in
	// one batch.  Note that 62 is the largest number of chunks that fit
	// into 64kiB on disk because chunkHeaderLen is added to each 1k chunk.

	indexingMaxBatchSize  = 1024 * 1024
	indexingBatchTimeout  = 500 * time.Millisecond // Commit batch when idle for that long.
	indexingQueueCapacity = 1024 * 16
)

var fpLen = len(model.Fingerprint(0).String()) // Length of a fingerprint as string.

const (
	flagHeadChunkPersisted byte = 1 << iota
	// Add more flags here like:
	// flagFoo
	// flagBar
)

type indexingOpType byte

const (
	add indexingOpType = iota
	remove
)

func (p *persistence) cleanUpArchiveIndexes(
	fpToSeries map[model.Fingerprint]*memorySeries,
	fpsSeen map[model.Fingerprint]struct{},
	fpm fpMappings,
) error {
	log.Info("Cleaning up archive indexes.")
	var fp codable.Fingerprint
	var m codable.Metric
	count := 0
	if err := p.archivedFingerprintToMetrics.ForEach(func(kv index.KeyValueAccessor) error {
		count++
		if count%10000 == 0 {
			log.Infof("%d archived metrics checked.", count)
		}
		if err := kv.Key(&fp); err != nil {
			return err
		}
		_, fpSeen := fpsSeen[model.Fingerprint(fp)]
		inMemory := false
		if fpSeen {
			_, inMemory = fpToSeries[model.Fingerprint(fp)]
		}
		if !fpSeen || inMemory {
			if inMemory {
				log.Warnf("Archive clean-up: Fingerprint %v is not archived. Purging from archive indexes.", model.Fingerprint(fp))
			}
			if !fpSeen {
				log.Warnf("Archive clean-up: Fingerprint %v is unknown. Purging from archive indexes.", model.Fingerprint(fp))
			}
			// It's fine if the fp is not in the archive indexes.
			if _, err := p.archivedFingerprintToMetrics.Delete(fp); err != nil {
				return err
			}
			// Delete from timerange index, too.
			_, err := p.archivedFingerprintToTimeRange.Delete(fp)
			return err
		}
		// fp is legitimately archived. Now we need the metric to check for a mapped fingerprint.
		if err := kv.Value(&m); err != nil {
			return err
		}
		maybeAddMapping(model.Fingerprint(fp), model.Metric(m), fpm)
		// Make sure it is in timerange index, too.
		has, err := p.archivedFingerprintToTimeRange.Has(fp)
		if err != nil {
			return err
		}
		if has {
			return nil // All good.
		}
		log.Warnf("Archive clean-up: Fingerprint %v is not in time-range index. Unarchiving it for recovery.")
		// Again, it's fine if fp is not in the archive index.
		if _, err := p.archivedFingerprintToMetrics.Delete(fp); err != nil {
			return err
		}
		cds, err := p.loadChunkDescs(model.Fingerprint(fp), 0)
		if err != nil {
			return err
		}
		series, err := newMemorySeries(model.Metric(m), cds, p.seriesFileModTime(model.Fingerprint(fp)))
		if err != nil {
			return err
		}
		fpToSeries[model.Fingerprint(fp)] = series
		return nil
	}); err != nil {
		return err
	}
	count = 0
	if err := p.archivedFingerprintToTimeRange.ForEach(func(kv index.KeyValueAccessor) error {
		count++
		if count%10000 == 0 {
			log.Infof("%d archived time ranges checked.", count)
		}
		if err := kv.Key(&fp); err != nil {
			return err
		}
		has, err := p.archivedFingerprintToMetrics.Has(fp)
		if err != nil {
			return err
		}
		if has {
			return nil // All good.
		}
		log.Warnf("Archive clean-up: Purging unknown fingerprint %v in time-range index.", fp)
		deleted, err := p.archivedFingerprintToTimeRange.Delete(fp)
		if err != nil {
			return err
		}
		if !deleted {
			log.Errorf("Fingerprint %v to be deleted from archivedFingerprintToTimeRange not found. This should never happen.", fp)
		}
		return nil
	}); err != nil {
		return err
	}
	log.Info("Clean-up of archive indexes complete.")
	return nil
}

// loadSeriesMapAndHeads loads the fingerprint to memory-series mapping and all
// the chunks contained in the checkpoint (and thus not yet persisted to series
// files). The method is capable of loading the checkpoint format v1 and v2. If
// recoverable corruption is detected, or if the dirty flag was set from the
// beginning, crash recovery is run, which might take a while. If an
// unrecoverable error is encountered, it is returned. Call this method during
// start-up while nothing else is running in storage land. This method is
// utterly goroutine-unsafe.
func (p *persistence) loadSeriesMapAndHeads() (sm *seriesMap, chunksToPersist int64, err error) {
	var chunkDescsTotal int64
	fingerprintToSeries := make(map[model.Fingerprint]*memorySeries)
	sm = &seriesMap{m: fingerprintToSeries}

	defer func() {
		if sm != nil && p.dirty {
			log.Warn("Persistence layer appears dirty.")
			err = p.recoverFromCrash(fingerprintToSeries)
			if err != nil {
				sm = nil
			}
		}
		if err == nil {
			numMemChunkDescs.Add(float64(chunkDescsTotal))
		}
	}()

	f, err := os.Open(p.headsFileName())
	if os.IsNotExist(err) {
		return sm, 0, nil
	}
	if err != nil {
		log.Warn("Could not open heads file:", err)
		p.dirty = true
		return
	}
	defer f.Close()
	r := bufio.NewReaderSize(f, fileBufSize)

	buf := make([]byte, len(headsMagicString))
	if _, err := io.ReadFull(r, buf); err != nil {
		log.Warn("Could not read from heads file:", err)
		p.dirty = true
		return sm, 0, nil
	}
	magic := string(buf)
	if magic != headsMagicString {
		log.Warnf(
			"unexpected magic string, want %q, got %q",
			headsMagicString, magic,
		)
		p.dirty = true
		return
	}
	version, err := binary.ReadVarint(r)
	if (version != headsFormatVersion && version != headsFormatLegacyVersion) || err != nil {
		log.Warnf("unknown heads format version, want %d", headsFormatVersion)
		p.dirty = true
		return sm, 0, nil
	}
	numSeries, err := codable.DecodeUint64(r)
	if err != nil {
		log.Warn("Could not decode number of series:", err)
		p.dirty = true
		return sm, 0, nil
	}

	for ; numSeries > 0; numSeries-- {
		seriesFlags, err := r.ReadByte()
		if err != nil {
			log.Warn("Could not read series flags:", err)
			p.dirty = true
			return sm, chunksToPersist, nil
		}
		headChunkPersisted := seriesFlags&flagHeadChunkPersisted != 0
		fp, err := codable.DecodeUint64(r)
		if err != nil {
			log.Warn("Could not decode fingerprint:", err)
			p.dirty = true
			return sm, chunksToPersist, nil
		}
		var metric codable.Metric
		if err := metric.UnmarshalFromReader(r); err != nil {
			log.Warn("Could not decode metric:", err)
			p.dirty = true
			return sm, chunksToPersist, nil
		}
		var persistWatermark int64
		var modTime time.Time
		if version != headsFormatLegacyVersion {
			// persistWatermark only present in v2.
			persistWatermark, err = binary.ReadVarint(r)
			if err != nil {
				log.Warn("Could not decode persist watermark:", err)
				p.dirty = true
				return sm, chunksToPersist, nil
			}
			modTimeNano, err := binary.ReadVarint(r)
			if err != nil {
				log.Warn("Could not decode modification time:", err)
				p.dirty = true
//.........这里部分代码省略.........