11 files changed, 521 insertions, 25 deletions

diff --git a/weed/storage/erasure_coding/1.dat b/weed/storage/erasure_coding/1.dat
new file mode 100644
index 000000000..869427926
--- /dev/null
+++ b/weed/storage/erasure_coding/1.dat
diff --git a/weed/storage/erasure_coding/1.idx b/weed/storage/erasure_coding/1.idx
new file mode 100644
index 000000000..65a950e64
--- /dev/null
+++ b/weed/storage/erasure_coding/1.idx
diff --git a/weed/storage/erasure_coding/ec_encoder.go b/weed/storage/erasure_coding/ec_encoder.go
new file mode 100644
index 000000000..4b5205dee
--- /dev/null
+++ b/weed/storage/erasure_coding/ec_encoder.go
@@ -0,0 +1,92 @@
+package erasure_coding
+
+import (
+	"fmt"
+	"io"
+	"os"
+
+	"github.com/chrislusf/seaweedfs/weed/glog"
+	"github.com/klauspost/reedsolomon"
+)
+
+const (
+	DataShardsCount             = 10
+	ParityShardsCount           = 4
+	ErasureCodingLargeBlockSize = 1024 * 1024 * 1024 // 1GB
+	ErasureCodingSmallBlockSize = 1024 * 1024        // 1MB
+)
+
+func encodeData(file *os.File, enc reedsolomon.Encoder, startOffset, blockSize int64, buffers [][]byte, outputs []*os.File) error {
+
+	bufferSize := int64(len(buffers[0]))
+	batchCount := blockSize/bufferSize
+	if blockSize%bufferSize!=0 {
+		glog.Fatalf("unexpected block size %d buffer size %d", blockSize, bufferSize)
+	}
+
+	for b := int64(0); b < batchCount; b++ {
+		err := encodeDataOneBatch(file, enc, startOffset+b*bufferSize, blockSize, buffers, outputs)
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func openEcFiles(baseFileName string, forRead bool) (files []*os.File, err error){
+	for i := 0; i< DataShardsCount+ParityShardsCount; i++{
+		fname := fmt.Sprintf("%s.ec%02d", baseFileName, i+1)
+		openOption := os.O_TRUNC|os.O_CREATE|os.O_WRONLY
+		if forRead {
+			openOption = os.O_RDONLY
+		}
+		f, err := os.OpenFile(fname, openOption, 0644)
+		if err != nil {
+			return files, fmt.Errorf("failed to open file %s: %v", fname, err)
+		}
+		files = append(files, f)
+	}
+	return
+}
+
+func closeEcFiles(files []*os.File){
+	for _, f := range files{
+		if f != nil {
+			f.Close()
+		}
+	}
+}
+
+
+func encodeDataOneBatch(file *os.File, enc reedsolomon.Encoder, startOffset, blockSize int64, buffers [][]byte, outputs []*os.File) error {
+
+	// read data into buffers
+	for i := 0; i < DataShardsCount; i++ {
+		n, err := file.ReadAt(buffers[i], startOffset+blockSize*int64(i))
+		if err != nil {
+			if err != io.EOF {
+				return err
+			}
+		}
+		if n < len(buffers[i]) {
+			for t := len(buffers[i]) - 1; t >= n; t-- {
+				buffers[i][t] = 0
+			}
+		}
+	}
+
+	err := enc.Encode(buffers)
+	if err != nil {
+		return err
+	}
+
+	for i := 0; i < DataShardsCount+ParityShardsCount; i++ {
+		_, err := outputs[i].Write(buffers[i])
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
diff --git a/weed/storage/erasure_coding/ec_locate.go b/weed/storage/erasure_coding/ec_locate.go
new file mode 100644
index 000000000..b570f750c
--- /dev/null
+++ b/weed/storage/erasure_coding/ec_locate.go
@@ -0,0 +1,68 @@
+package erasure_coding
+
+type Interval struct {
+	blockIndex       int
+	innerBlockOffset int64
+	size             uint32
+	isLargeBlock     bool
+}
+
+func locateData(largeBlockLength, smallBlockLength int64, datSize int64, offset int64, size uint32) (intervals []Interval) {
+	blockIndex, isLargeBlock, innerBlockOffset := locateOffset(largeBlockLength, smallBlockLength, datSize, offset)
+
+	nLargeBlockRows := int(datSize / (largeBlockLength * DataShardsCount))
+
+	for size > 0 {
+		interval := Interval{
+			blockIndex:       blockIndex,
+			innerBlockOffset: innerBlockOffset,
+			isLargeBlock:     isLargeBlock,
+		}
+
+		blockRemaining := largeBlockLength - innerBlockOffset
+		if !isLargeBlock {
+			blockRemaining = smallBlockLength - innerBlockOffset
+		}
+
+		if int64(size) <= blockRemaining {
+			interval.size = size
+			intervals = append(intervals, interval)
+			return
+		}
+		interval.size = uint32(blockRemaining)
+		intervals = append(intervals, interval)
+
+		size -= interval.size
+		blockIndex += 1
+		if isLargeBlock && blockIndex == nLargeBlockRows*DataShardsCount {
+			isLargeBlock = false
+			blockIndex = 0
+		}
+		innerBlockOffset = 0
+
+	}
+	return
+}
+
+func locateOffset(largeBlockLength, smallBlockLength int64, datSize int64, offset int64) (blockIndex int, isLargeBlock bool, innerBlockOffset int64) {
+	largeRowSize := largeBlockLength * DataShardsCount
+	nLargeBlockRows := datSize / (largeBlockLength * DataShardsCount)
+
+	// if offset is within the large block area
+	if offset < nLargeBlockRows*largeRowSize {
+		isLargeBlock = true
+		blockIndex, innerBlockOffset = locateOffsetWithinBlocks(largeBlockLength, offset)
+		return
+	}
+
+	isLargeBlock = false
+	offset -= nLargeBlockRows * largeRowSize
+	blockIndex, innerBlockOffset = locateOffsetWithinBlocks(smallBlockLength, offset)
+	return
+}
+
+func locateOffsetWithinBlocks(blockLength int64, offset int64) (blockIndex int, innerBlockOffset int64) {
+	blockIndex = int(offset / blockLength)
+	innerBlockOffset = offset % blockLength
+	return
+}
diff --git a/weed/storage/erasure_coding/ec_test.go b/weed/storage/erasure_coding/ec_test.go
new file mode 100644
index 000000000..d631471e9
--- /dev/null
+++ b/weed/storage/erasure_coding/ec_test.go
@@ -0,0 +1,312 @@
+package erasure_coding
+
+import (
+	"bytes"
+	"fmt"
+	"math/rand"
+	"os"
+	"testing"
+
+	"github.com/chrislusf/seaweedfs/weed/storage"
+	"github.com/chrislusf/seaweedfs/weed/storage/needle_map"
+	"github.com/chrislusf/seaweedfs/weed/storage/types"
+	"github.com/klauspost/reedsolomon"
+)
+
+const (
+	largeBlockSize = 10000
+	smallBlockSize = 100
+)
+
+func TestEncodingDecoding(t *testing.T) {
+	bufferSize := 50
+	baseFileName := "1"
+
+	err := generateEcFiles(baseFileName, bufferSize, largeBlockSize, smallBlockSize)
+	if err != nil {
+		t.Logf("generateEcFiles: %v", err)
+	}
+
+	err = writeSortedEcxFiles(baseFileName)
+	if err != nil {
+		t.Logf("writeSortedEcxFiles: %v", err)
+	}
+
+	err = validateFiles(baseFileName)
+	if err != nil {
+		t.Logf("writeSortedEcxFiles: %v", err)
+	}
+
+	removeGeneratedFiles(baseFileName)
+
+}
+
+func generateEcFiles(baseFileName string, bufferSize int, largeBlockSize int64, smallBlockSize int64) error {
+	file, err := os.OpenFile(baseFileName+".dat", os.O_RDONLY, 0)
+	if err != nil {
+		return fmt.Errorf("failed to open dat file: %v", err)
+	}
+	defer file.Close()
+
+	fi, err := file.Stat()
+	if err != nil {
+		return fmt.Errorf("failed to stat dat file: %v", err)
+	}
+	err = encodeDatFile(fi.Size(), err, baseFileName, bufferSize, largeBlockSize, file, smallBlockSize)
+	if err != nil {
+		return fmt.Errorf("encodeDatFile: %v", err)
+	}
+	return nil
+}
+
+func encodeDatFile(remainingSize int64, err error, baseFileName string, bufferSize int, largeBlockSize int64, file *os.File, smallBlockSize int64) error {
+	var processedSize int64
+	enc, err := reedsolomon.New(DataShardsCount, ParityShardsCount)
+	if err != nil {
+		return fmt.Errorf("failed to create encoder: %v", err)
+	}
+	buffers := make([][]byte, DataShardsCount+ParityShardsCount)
+	outputs, err := openEcFiles(baseFileName, false)
+	defer closeEcFiles(outputs)
+	if err != nil {
+		return fmt.Errorf("failed to open dat file: %v", err)
+	}
+	for i, _ := range buffers {
+		buffers[i] = make([]byte, bufferSize)
+	}
+	for remainingSize > largeBlockSize*DataShardsCount {
+		err = encodeData(file, enc, processedSize, largeBlockSize, buffers, outputs)
+		if err != nil {
+			return fmt.Errorf("failed to encode large chunk data: %v", err)
+		}
+		remainingSize -= largeBlockSize * DataShardsCount
+		processedSize += largeBlockSize * DataShardsCount
+	}
+	for remainingSize > 0 {
+		encodeData(file, enc, processedSize, smallBlockSize, buffers, outputs)
+		if err != nil {
+			return fmt.Errorf("failed to encode small chunk data: %v", err)
+		}
+		remainingSize -= smallBlockSize * DataShardsCount
+		processedSize += smallBlockSize * DataShardsCount
+	}
+	return nil
+}
+
+func writeSortedEcxFiles(baseFileName string) (e error) {
+
+	cm, err := readCompactMap(baseFileName)
+	if err != nil {
+		return fmt.Errorf("readCompactMap: %v", err)
+	}
+
+	ecxFile, err := os.OpenFile(baseFileName+".ecx", os.O_TRUNC|os.O_CREATE|os.O_WRONLY, 0644)
+	if err != nil {
+		return fmt.Errorf("failed to open dat file: %v", err)
+	}
+	defer ecxFile.Close()
+
+	err = cm.AscendingVisit(func(value needle_map.NeedleValue) error {
+		bytes := value.ToBytes()
+		_, writeErr := ecxFile.Write(bytes)
+		return writeErr
+	})
+
+	if err != nil {
+		return fmt.Errorf("failed to open dat file: %v", err)
+	}
+
+	return nil
+}
+
+func validateFiles(baseFileName string) error {
+	cm, err := readCompactMap(baseFileName)
+	if err != nil {
+		return fmt.Errorf("readCompactMap: %v", err)
+	}
+
+	datFile, err := os.OpenFile(baseFileName+".dat", os.O_RDONLY, 0)
+	if err != nil {
+		return fmt.Errorf("failed to open dat file: %v", err)
+	}
+	defer datFile.Close()
+
+	fi, err := datFile.Stat()
+	if err != nil {
+		return fmt.Errorf("failed to stat dat file: %v", err)
+	}
+
+	ecFiles, err := openEcFiles(baseFileName, true)
+	defer closeEcFiles(ecFiles)
+
+	err = cm.AscendingVisit(func(value needle_map.NeedleValue) error {
+		return assertSame(datFile, fi.Size(), ecFiles, value.Offset, value.Size)
+	})
+	if err != nil {
+		return fmt.Errorf("failed to check ec files: %v", err)
+	}
+	return nil
+}
+
+func readCompactMap(baseFileName string) (*needle_map.CompactMap, error) {
+	indexFile, err := os.OpenFile(baseFileName+".idx", os.O_RDONLY, 0644)
+	if err != nil {
+		return nil, fmt.Errorf("cannot read Volume Index %s.idx: %v", baseFileName, err)
+	}
+	defer indexFile.Close()
+
+	cm := needle_map.NewCompactMap()
+	err = storage.WalkIndexFile(indexFile, func(key types.NeedleId, offset types.Offset, size uint32) error {
+		if !offset.IsZero() && size != types.TombstoneFileSize {
+			cm.Set(key, offset, size)
+		} else {
+			cm.Delete(key)
+		}
+		return nil
+	})
+	return cm, err
+}
+
+func assertSame(datFile *os.File, datSize int64, ecFiles []*os.File, offset types.Offset, size uint32) error {
+
+	data, err := readDatFile(datFile, offset, size)
+	if err != nil {
+		return fmt.Errorf("failed to read dat file: %v", err)
+	}
+
+	ecData, err := readEcFile(datSize, ecFiles, offset, size)
+	if err != nil {
+		return fmt.Errorf("failed to read ec file: %v", err)
+	}
+
+	if bytes.Compare(data, ecData) != 0 {
+		return fmt.Errorf("unexpected data read")
+	}
+
+	return nil
+}
+
+func readDatFile(datFile *os.File, offset types.Offset, size uint32) ([]byte, error) {
+
+	data := make([]byte, size)
+	n, err := datFile.ReadAt(data, offset.ToAcutalOffset())
+	if err != nil {
+		return nil, fmt.Errorf("failed to ReadAt dat file: %v", err)
+	}
+	if n != int(size) {
+		return nil, fmt.Errorf("unexpected read size %d, expected %d", n, size)
+	}
+	return data, nil
+}
+
+func readEcFile(datSize int64, ecFiles []*os.File, offset types.Offset, size uint32) (data []byte, err error) {
+
+	intervals := locateData(largeBlockSize, smallBlockSize, datSize, offset.ToAcutalOffset(), size)
+
+	nLargeBlockRows := int(datSize / (largeBlockSize * DataShardsCount))
+
+	for i, interval := range intervals {
+		if d, e := readOneInterval(interval, ecFiles, nLargeBlockRows); e != nil {
+			return nil, e
+		} else {
+			if i == 0 {
+				data = d
+			} else {
+				data = append(data, d...)
+			}
+		}
+	}
+
+	return data, nil
+}
+
+func readOneInterval(interval Interval, ecFiles []*os.File, nLargeBlockRows int) (data []byte, err error) {
+	ecFileOffset := interval.innerBlockOffset
+	rowIndex := interval.blockIndex / DataShardsCount
+	if interval.isLargeBlock {
+		ecFileOffset += int64(rowIndex) * largeBlockSize
+	} else {
+		ecFileOffset += int64(nLargeBlockRows)*largeBlockSize + int64(rowIndex)*smallBlockSize
+	}
+
+	ecFileIndex := interval.blockIndex % DataShardsCount
+
+	data = make([]byte, interval.size)
+	err = readFromFile(ecFiles[ecFileIndex], data, ecFileOffset)
+	{ // do some ec testing
+		ecData, err := readFromOtherEcFiles(ecFiles, ecFileIndex, ecFileOffset, interval.size)
+		if err != nil {
+			return nil, fmt.Errorf("ec reconstruct error: %v", err)
+		}
+		if bytes.Compare(data, ecData) != 0 {
+			return nil, fmt.Errorf("ec compare error")
+		}
+	}
+	return
+}
+
+func readFromOtherEcFiles(ecFiles []*os.File, ecFileIndex int, ecFileOffset int64, size uint32) (data []byte, err error) {
+	enc, err := reedsolomon.New(DataShardsCount, ParityShardsCount)
+	if err != nil {
+		return nil, fmt.Errorf("failed to create encoder: %v", err)
+	}
+
+	bufs := make([][]byte, DataShardsCount+ParityShardsCount)
+	for i := 0; i < DataShardsCount; {
+		n := int(rand.Int31n(DataShardsCount + ParityShardsCount))
+		if n == ecFileIndex || bufs[n] != nil {
+			continue
+		}
+		bufs[n] = make([]byte, size)
+		i++
+	}
+
+	for i, buf := range bufs {
+		if buf == nil {
+			continue
+		}
+		err = readFromFile(ecFiles[i], buf, ecFileOffset)
+		if err != nil {
+			return
+		}
+	}
+
+	if err = enc.ReconstructData(bufs); err != nil {
+		return nil, err
+	}
+
+	return bufs[ecFileIndex], nil
+}
+
+func readFromFile(file *os.File, data []byte, ecFileOffset int64) (err error) {
+	_, err = file.ReadAt(data, ecFileOffset)
+	return
+}
+
+func removeGeneratedFiles(baseFileName string) {
+	for i := 0; i < DataShardsCount+ParityShardsCount; i++ {
+		fname := fmt.Sprintf("%s.ec%02d", baseFileName, i+1)
+		os.Remove(fname)
+	}
+	os.Remove(baseFileName+".ecx")
+}
+
+func TestLocateData(t *testing.T) {
+	intervals := locateData(largeBlockSize, smallBlockSize, DataShardsCount*largeBlockSize+1, DataShardsCount*largeBlockSize, 1)
+	if len(intervals) != 1 {
+		t.Errorf("unexpected interval size %d", len(intervals))
+	}
+	if !intervals[0].sameAs(Interval{0, 0, 1, false}) {
+		t.Errorf("unexpected interval %+v", intervals[0])
+	}
+
+	intervals = locateData(largeBlockSize, smallBlockSize, DataShardsCount*largeBlockSize+1, DataShardsCount*largeBlockSize/2+100, DataShardsCount*largeBlockSize+1-DataShardsCount*largeBlockSize/2-100)
+	fmt.Printf("%+v\n", intervals)
+}
+
+func (this Interval) sameAs(that Interval) bool {
+	return this.isLargeBlock == that.isLargeBlock &&
+		this.innerBlockOffset == that.innerBlockOffset &&
+		this.blockIndex == that.blockIndex &&
+		this.size == that.size
+}
diff --git a/weed/storage/needle_map.go b/weed/storage/needle_map.go
index 634685175..f2c88093f 100644
--- a/weed/storage/needle_map.go
+++ b/weed/storage/needle_map.go
@@ -62,10 +62,7 @@ func IdxFileEntry(bytes []byte) (key NeedleId, offset Offset, size uint32) {
 	return
 }
 func (nm *baseNeedleMapper) appendToIndexFile(key NeedleId, offset Offset, size uint32) error {
-	bytes := make([]byte, NeedleIdSize+OffsetSize+SizeSize)
-	NeedleIdToBytes(bytes[0:NeedleIdSize], key)
-	OffsetToBytes(bytes[NeedleIdSize:NeedleIdSize+OffsetSize], offset)
-	util.Uint32toBytes(bytes[NeedleIdSize+OffsetSize:NeedleIdSize+OffsetSize+SizeSize], size)
+	bytes := needle_map.ToBytes(key, offset, size)
 
 	nm.indexFileAccessLock.Lock()
 	defer nm.indexFileAccessLock.Unlock()
@@ -76,6 +73,7 @@ func (nm *baseNeedleMapper) appendToIndexFile(key NeedleId, offset Offset, size
 	_, err := nm.indexFile.Write(bytes)
 	return err
 }
+
 func (nm *baseNeedleMapper) IndexFileContent() ([]byte, error) {
 	nm.indexFileAccessLock.Lock()
 	defer nm.indexFileAccessLock.Unlock()
diff --git a/weed/storage/needle_map/btree_map.go b/weed/storage/needle_map/btree_map.go
index 74b4952b7..a26c5e068 100644
--- a/weed/storage/needle_map/btree_map.go
+++ b/weed/storage/needle_map/btree_map.go
@@ -43,7 +43,7 @@ func (cm *BtreeMap) Get(key NeedleId) (*NeedleValue, bool) {
 }
 
 // Visit visits all entries or stop if any error when visiting
-func (cm *BtreeMap) Visit(visit func(NeedleValue) error) (ret error) {
+func (cm *BtreeMap) AscendingVisit(visit func(NeedleValue) error) (ret error) {
 	cm.tree.Ascend(func(item btree.Item) bool {
 		needle := item.(NeedleValue)
 		ret = visit(needle)
diff --git a/weed/storage/needle_map/compact_map.go b/weed/storage/needle_map/compact_map.go
index 193d17e47..8aee51ec9 100644
--- a/weed/storage/needle_map/compact_map.go
+++ b/weed/storage/needle_map/compact_map.go
@@ -244,24 +244,37 @@ func (cm *CompactMap) binarySearchCompactSection(key NeedleId) int {
 }
 
 // Visit visits all entries or stop if any error when visiting
-func (cm *CompactMap) Visit(visit func(NeedleValue) error) error {
+func (cm *CompactMap) AscendingVisit(visit func(NeedleValue) error) error {
 	for _, cs := range cm.list {
 		cs.RLock()
-		for i, v := range cs.overflow {
-			if err := visit(toNeedleValue(cs.overflowExtra[i], v, cs)); err != nil {
+		var i, j int
+		for i, j = 0, 0; i < len(cs.overflow) && j < len(cs.values) && j<cs.counter; {
+			if cs.overflow[i].Key < cs.values[j].Key {
+				if err := visit(toNeedleValue(cs.overflowExtra[i], cs.overflow[i], cs)); err != nil {
+					cs.RUnlock()
+					return err
+				}
+				i++
+			}else if cs.overflow[i].Key == cs.values[j].Key {
+				j++
+			}else{
+				if err := visit(toNeedleValue(cs.valuesExtra[j], cs.values[j], cs)); err != nil {
+					cs.RUnlock()
+					return err
+				}
+				j++
+			}
+		}
+		for ;i < len(cs.overflow);i++{
+			if err := visit(toNeedleValue(cs.overflowExtra[i], cs.overflow[i], cs)); err != nil {
 				cs.RUnlock()
 				return err
 			}
 		}
-		for i, v := range cs.values {
-			if i >= cs.counter {
-				break
-			}
-			if _, _, found := cs.findOverflowEntry(v.Key); !found {
-				if err := visit(toNeedleValue(cs.valuesExtra[i], v, cs)); err != nil {
-					cs.RUnlock()
-					return err
-				}
+		for ; j < len(cs.values)&& j<cs.counter;j++{
+			if err := visit(toNeedleValue(cs.valuesExtra[j], cs.values[j], cs)); err != nil {
+				cs.RUnlock()
+				return err
 			}
 		}
 		cs.RUnlock()
@@ -279,10 +292,10 @@ func toNeedleValue(snve SectionalNeedleValueExtra, snv SectionalNeedleValue, cs
 
 func (nv NeedleValue) toSectionalNeedleValue(cs *CompactSection) (SectionalNeedleValue, SectionalNeedleValueExtra) {
 	return SectionalNeedleValue{
-			SectionalNeedleId(nv.Key - cs.start),
-			nv.Offset.OffsetLower,
-			nv.Size,
-		}, SectionalNeedleValueExtra{
-			nv.Offset.OffsetHigher,
-		}
+		SectionalNeedleId(nv.Key - cs.start),
+		nv.Offset.OffsetLower,
+		nv.Size,
+	}, SectionalNeedleValueExtra{
+		nv.Offset.OffsetHigher,
+	}
 }
diff --git a/weed/storage/needle_map/compact_map_test.go b/weed/storage/needle_map/compact_map_test.go
index 4894e59ad..3bad85727 100644
--- a/weed/storage/needle_map/compact_map_test.go
+++ b/weed/storage/needle_map/compact_map_test.go
@@ -19,7 +19,7 @@ func TestOverflow2(t *testing.T) {
 	m.Set(NeedleId(150158), ToOffset(8), 3000073)
 	m.Set(NeedleId(150162), ToOffset(8), 3000073)
 
-	m.Visit(func(value NeedleValue) error {
+	m.AscendingVisit(func(value NeedleValue) error {
 		println("needle key:", value.Key)
 		return nil
 	})
diff --git a/weed/storage/needle_map/needle_value.go b/weed/storage/needle_map/needle_value.go
index d0c0b9006..ef540b55e 100644
--- a/weed/storage/needle_map/needle_value.go
+++ b/weed/storage/needle_map/needle_value.go
@@ -2,6 +2,7 @@ package needle_map
 
 import (
 	. "github.com/chrislusf/seaweedfs/weed/storage/types"
+	"github.com/chrislusf/seaweedfs/weed/util"
 	"github.com/google/btree"
 )
 
@@ -15,3 +16,15 @@ func (this NeedleValue) Less(than btree.Item) bool {
 	that := than.(NeedleValue)
 	return this.Key < that.Key
 }
+
+func (nv NeedleValue) ToBytes() []byte {
+	return ToBytes(nv.Key, nv.Offset, nv.Size)
+}
+
+func ToBytes(key NeedleId, offset Offset, size uint32) []byte {
+	bytes := make([]byte, NeedleIdSize+OffsetSize+SizeSize)
+	NeedleIdToBytes(bytes[0:NeedleIdSize], key)
+	OffsetToBytes(bytes[NeedleIdSize:NeedleIdSize+OffsetSize], offset)
+	util.Uint32toBytes(bytes[NeedleIdSize+OffsetSize:NeedleIdSize+OffsetSize+SizeSize], size)
+	return bytes
+}
diff --git a/weed/storage/needle_map/needle_value_map.go b/weed/storage/needle_map/needle_value_map.go
index acf38a4bf..0a5a00ef7 100644
--- a/weed/storage/needle_map/needle_value_map.go
+++ b/weed/storage/needle_map/needle_value_map.go
@@ -8,5 +8,5 @@ type NeedleValueMap interface {
 	Set(key NeedleId, offset Offset, size uint32) (oldOffset Offset, oldSize uint32)
 	Delete(key NeedleId) uint32
 	Get(key NeedleId) (*NeedleValue, bool)
-	Visit(visit func(NeedleValue) error) error
+	AscendingVisit(visit func(NeedleValue) error) error
 }