add stream writer

this should improve streaming write performance, which is common in many cases, e.g., copying large files.

This is additional to improved random read write operations: 3e69d19380...19084d8791

weed/filesys/dirty_pages_stream.go

@@ -0,0 +1,107 @@
+package filesys
+
+import (
+	"fmt"
+	"github.com/chrislusf/seaweedfs/weed/filesys/page_writer"
+	"github.com/chrislusf/seaweedfs/weed/glog"
+	"github.com/chrislusf/seaweedfs/weed/pb/filer_pb"
+	"io"
+	"sync"
+	"time"
+)
+
+type StreamDirtyPages struct {
+	f              *File
+	writeWaitGroup sync.WaitGroup
+	pageAddLock    sync.Mutex
+	chunkAddLock   sync.Mutex
+	lastErr        error
+	collection     string
+	replication    string
+	chunkedStream  *page_writer.ChunkedStreamWriter
+}
+
+func newStreamDirtyPages(file *File, chunkSize int64) *StreamDirtyPages {
+
+	dirtyPages := &StreamDirtyPages{
+		f:             file,
+		chunkedStream: page_writer.NewChunkedStreamWriter(chunkSize),
+	}
+
+	dirtyPages.chunkedStream.SetSaveToStorageFunction(dirtyPages.saveChunkedFileIntevalToStorage)
+
+	return dirtyPages
+}
+
+func (pages *StreamDirtyPages) AddPage(offset int64, data []byte) {
+
+	pages.pageAddLock.Lock()
+	defer pages.pageAddLock.Unlock()
+
+	glog.V(4).Infof("%v stream AddPage [%d, %d)", pages.f.fullpath(), offset, offset+int64(len(data)))
+	if _, err := pages.chunkedStream.WriteAt(data, offset); err != nil {
+		pages.lastErr = err
+	}
+
+	return
+}
+
+func (pages *StreamDirtyPages) FlushData() error {
+	pages.saveChunkedFileToStorage()
+	pages.writeWaitGroup.Wait()
+	if pages.lastErr != nil {
+		return fmt.Errorf("flush data: %v", pages.lastErr)
+	}
+	pages.chunkedStream.Reset()
+	return nil
+}
+
+func (pages *StreamDirtyPages) ReadDirtyDataAt(data []byte, startOffset int64) (maxStop int64) {
+	return pages.chunkedStream.ReadDataAt(data, startOffset)
+}
+
+func (pages *StreamDirtyPages) GetStorageOptions() (collection, replication string) {
+	return pages.collection, pages.replication
+}
+
+func (pages *StreamDirtyPages) saveChunkedFileToStorage() {
+
+	pages.chunkedStream.FlushAll()
+
+}
+
+func (pages *StreamDirtyPages) saveChunkedFileIntevalToStorage(reader io.Reader, offset int64, size int64, cleanupFn func()) {
+
+	mtime := time.Now().UnixNano()
+	pages.writeWaitGroup.Add(1)
+	writer := func() {
+		defer pages.writeWaitGroup.Done()
+		defer cleanupFn()
+
+		chunk, collection, replication, err := pages.f.wfs.saveDataAsChunk(pages.f.fullpath())(reader, pages.f.Name, offset)
+		if err != nil {
+			glog.V(0).Infof("%s saveToStorage [%d,%d): %v", pages.f.fullpath(), offset, offset+size, err)
+			pages.lastErr = err
+			return
+		}
+		chunk.Mtime = mtime
+		pages.collection, pages.replication = collection, replication
+		pages.chunkAddLock.Lock()
+		pages.f.addChunks([]*filer_pb.FileChunk{chunk})
+		glog.V(3).Infof("%s saveToStorage %s [%d,%d)", pages.f.fullpath(), chunk.FileId, offset, offset+size)
+		pages.chunkAddLock.Unlock()
+
+		cleanupFn()
+	}
+
+	if pages.f.wfs.concurrentWriters != nil {
+		pages.f.wfs.concurrentWriters.Execute(writer)
+	} else {
+		go writer()
+	}
+
+}
+
+func (pages StreamDirtyPages) Destroy() {
+	pages.chunkedStream.Reset()
+}

weed/filesys/dirty_pages_temp_file.go

@@ -37,6 +37,7 @@ func (pages *TempFileDirtyPages) AddPage(offset int64, data []byte) {
 	pages.pageAddLock.Lock()
 	defer pages.pageAddLock.Unlock()
 
+	glog.V(4).Infof("%v tempfile AddPage [%d, %d)", pages.f.fullpath(), offset, offset+int64(len(data)))
 	if _, err := pages.chunkedFile.WriteAt(data, offset); err != nil {
 		pages.lastErr = err
 	}
@@ -50,6 +51,7 @@ func (pages *TempFileDirtyPages) FlushData() error {
 	if pages.lastErr != nil {
 		return fmt.Errorf("flush data: %v", pages.lastErr)
 	}
+	pages.chunkedFile.Reset()
 	return nil
 }
 
@@ -65,7 +67,7 @@ func (pages *TempFileDirtyPages) saveChunkedFileToStorage() {
 
 	pages.chunkedFile.ProcessEachInterval(func(file *os.File, logicChunkIndex page_writer.LogicChunkIndex, interval *page_writer.ChunkWrittenInterval) {
 		reader := page_writer.NewFileIntervalReader(pages.chunkedFile, logicChunkIndex, interval)
-		pages.saveChunkedFileIntevalToStorage(reader, int64(logicChunkIndex)*pages.chunkedFile.ChunkSize, interval.Size())
+		pages.saveChunkedFileIntevalToStorage(reader, int64(logicChunkIndex)*pages.chunkedFile.ChunkSize+interval.StartOffset, interval.Size())
 	})
 
 }
@@ -100,5 +102,5 @@ func (pages *TempFileDirtyPages) saveChunkedFileIntevalToStorage(reader io.Reade
 }
 
 func (pages TempFileDirtyPages) Destroy() {
-	pages.chunkedFile.Destroy()
+	pages.chunkedFile.Reset()
 }

weed/filesys/filehandle.go

@@ -27,6 +27,7 @@ type FileHandle struct {
 	contentType    string
 	handle         uint64
 	sync.Mutex
+	sync.WaitGroup
 
 	f         *File
 	RequestId fuse.RequestID // unique ID for request
@@ -41,7 +42,7 @@ func newFileHandle(file *File, uid, gid uint32) *FileHandle {
 	fh := &FileHandle{
 		f: file,
 		// dirtyPages: newContinuousDirtyPages(file, writeOnly),
-		dirtyPages: newPageWriter(file, 2*1024*1024),
+		dirtyPages: newPageWriter(file, file.wfs.option.CacheSizeMB*1024*1024),
 		Uid:        uid,
 		Gid:        gid,
 	}
@@ -63,6 +64,9 @@ var _ = fs.HandleReleaser(&FileHandle{})
 
 func (fh *FileHandle) Read(ctx context.Context, req *fuse.ReadRequest, resp *fuse.ReadResponse) error {
 
+	fh.Add(1)
+	defer fh.Done()
+
 	fh.Lock()
 	defer fh.Unlock()
 
@@ -170,6 +174,9 @@ func (fh *FileHandle) readFromChunks(buff []byte, offset int64) (int64, error) {
 // Write to the file handle
 func (fh *FileHandle) Write(ctx context.Context, req *fuse.WriteRequest, resp *fuse.WriteResponse) error {
 
+	fh.Add(1)
+	defer fh.Done()
+
 	fh.Lock()
 	defer fh.Unlock()
 
@@ -209,8 +216,7 @@ func (fh *FileHandle) Release(ctx context.Context, req *fuse.ReleaseRequest) err
 
 	glog.V(4).Infof("Release %v fh %d open=%d", fh.f.fullpath(), fh.handle, fh.f.isOpen)
 
-	fh.Lock()
-	defer fh.Unlock()
+	fh.Wait()
 
 	fh.f.wfs.handlesLock.Lock()
 	fh.f.isOpen--
@@ -243,6 +249,9 @@ func (fh *FileHandle) Flush(ctx context.Context, req *fuse.FlushRequest) error {
 		return nil
 	}
 
+	fh.Add(1)
+	defer fh.Done()
+
 	fh.Lock()
 	defer fh.Unlock()
 
@@ -251,7 +260,6 @@ func (fh *FileHandle) Flush(ctx context.Context, req *fuse.FlushRequest) error {
 		return err
 	}
 
-	glog.V(4).Infof("Flush %v fh %d success", fh.f.fullpath(), fh.handle)
 	return nil
 }
 

weed/filesys/page_writer.go

@@ -24,19 +24,21 @@ func newPageWriter(file *File, chunkSize int64) *PageWriter {
 	pw := &PageWriter{
 		f:             file,
 		chunkSize:     chunkSize,
+		writerPattern: NewWriterPattern(chunkSize),
 		randomWriter:  newTempFileDirtyPages(file, chunkSize),
-		streamWriter:  newContinuousDirtyPages(file),
-		writerPattern: NewWriterPattern(file.Name, chunkSize),
+		streamWriter:  newStreamDirtyPages(file, chunkSize),
+		//streamWriter: newContinuousDirtyPages(file),
+		//streamWriter:  nil,
 	}
 	return pw
 }
 
 func (pw *PageWriter) AddPage(offset int64, data []byte) {
 
-	glog.V(4).Infof("AddPage %v [%d, %d) streaming:%v", pw.f.fullpath(), offset, offset+int64(len(data)), pw.writerPattern.IsStreamingMode())
-
 	pw.writerPattern.MonitorWriteAt(offset, len(data))
 
+	glog.V(4).Infof("%v AddPage [%d, %d) streaming:%v", pw.f.fullpath(), offset, offset+int64(len(data)), pw.writerPattern.IsStreamingMode())
+
 	chunkIndex := offset / pw.chunkSize
 	for i := chunkIndex; len(data) > 0; i++ {
 		writeSize := min(int64(len(data)), (i+1)*pw.chunkSize-offset)
@@ -48,7 +50,7 @@ func (pw *PageWriter) AddPage(offset int64, data []byte) {
 
 func (pw *PageWriter) addToOneChunk(chunkIndex, offset int64, data []byte) {
 	if chunkIndex > 0 {
-		if pw.writerPattern.IsStreamingMode() {
+		if pw.writerPattern.IsStreamingMode() && pw.streamWriter != nil {
 			pw.streamWriter.AddPage(offset, data)
 			return
 		}
@@ -57,8 +59,11 @@ func (pw *PageWriter) addToOneChunk(chunkIndex, offset int64, data []byte) {
 }
 
 func (pw *PageWriter) FlushData() error {
-	if err := pw.streamWriter.FlushData(); err != nil {
-		return err
+	pw.writerPattern.Reset()
+	if pw.streamWriter != nil {
+		if err := pw.streamWriter.FlushData(); err != nil {
+			return err
+		}
 	}
 	return pw.randomWriter.FlushData()
 }
@@ -70,10 +75,12 @@ func (pw *PageWriter) ReadDirtyDataAt(data []byte, offset int64) (maxStop int64)
 	for i := chunkIndex; len(data) > 0; i++ {
 		readSize := min(int64(len(data)), (i+1)*pw.chunkSize-offset)
 
-		m1 := pw.streamWriter.ReadDirtyDataAt(data[:readSize], offset)
+		if pw.streamWriter != nil {
+			m1 := pw.streamWriter.ReadDirtyDataAt(data[:readSize], offset)
+			maxStop = max(maxStop, m1)
+		}
 		m2 := pw.randomWriter.ReadDirtyDataAt(data[:readSize], offset)
-
-		maxStop = max(maxStop, max(m1, m2))
+		maxStop = max(maxStop, m2)
 
 		offset += readSize
 		data = data[readSize:]
@@ -83,13 +90,16 @@ func (pw *PageWriter) ReadDirtyDataAt(data []byte, offset int64) (maxStop int64)
 }
 
 func (pw *PageWriter) GetStorageOptions() (collection, replication string) {
-	if pw.writerPattern.IsStreamingMode() {
+	if pw.writerPattern.IsStreamingMode() && pw.streamWriter != nil {
 		return pw.streamWriter.GetStorageOptions()
 	}
 	return pw.randomWriter.GetStorageOptions()
 }
 
 func (pw *PageWriter) Destroy() {
+	if pw.streamWriter != nil {
+		pw.streamWriter.Destroy()
+	}
 	pw.randomWriter.Destroy()
 }
 

weed/filesys/page_writer/chunk_interval_list.go

@@ -4,14 +4,18 @@ import "math"
 
 // ChunkWrittenInterval mark one written interval within one page chunk
 type ChunkWrittenInterval struct {
-	startOffset int64
+	StartOffset int64
 	stopOffset  int64
 	prev        *ChunkWrittenInterval
 	next        *ChunkWrittenInterval
 }
 
 func (interval *ChunkWrittenInterval) Size() int64 {
-	return interval.stopOffset - interval.startOffset
+	return interval.stopOffset - interval.StartOffset
+}
+
+func (interval *ChunkWrittenInterval) isComplete(chunkSize int64) bool {
+	return interval.stopOffset-interval.StartOffset == chunkSize
 }
 
 // ChunkWrittenIntervalList mark written intervals within one page chunk
@@ -23,11 +27,11 @@ type ChunkWrittenIntervalList struct {
 func newChunkWrittenIntervalList() *ChunkWrittenIntervalList {
 	list := &ChunkWrittenIntervalList{
 		head: &ChunkWrittenInterval{
-			startOffset: -1,
+			StartOffset: -1,
 			stopOffset:  -1,
 		},
 		tail: &ChunkWrittenInterval{
-			startOffset: math.MaxInt64,
+			StartOffset: math.MaxInt64,
 			stopOffset:  math.MaxInt64,
 		},
 	}
@@ -38,35 +42,40 @@ func newChunkWrittenIntervalList() *ChunkWrittenIntervalList {
 
 func (list *ChunkWrittenIntervalList) MarkWritten(startOffset, stopOffset int64) {
 	interval := &ChunkWrittenInterval{
-		startOffset: startOffset,
+		StartOffset: startOffset,
 		stopOffset:  stopOffset,
 	}
 	list.addInterval(interval)
 }
+
+func (list *ChunkWrittenIntervalList) IsComplete(chunkSize int64) bool {
+	return list.size() == 1 && list.head.next.isComplete(chunkSize)
+}
+
 func (list *ChunkWrittenIntervalList) addInterval(interval *ChunkWrittenInterval) {
 
 	p := list.head
-	for ; p.next != nil && p.next.startOffset <= interval.startOffset; p = p.next {
+	for ; p.next != nil && p.next.StartOffset <= interval.StartOffset; p = p.next {
 	}
 	q := list.tail
 	for ; q.prev != nil && q.prev.stopOffset >= interval.stopOffset; q = q.prev {
 	}
 
-	if interval.startOffset <= p.stopOffset && q.startOffset <= interval.stopOffset {
+	if interval.StartOffset <= p.stopOffset && q.StartOffset <= interval.stopOffset {
 		// merge p and q together
 		p.stopOffset = q.stopOffset
 		unlinkNodesBetween(p, q.next)
 		return
 	}
-	if interval.startOffset <= p.stopOffset {
+	if interval.StartOffset <= p.stopOffset {
 		// merge new interval into p
 		p.stopOffset = interval.stopOffset
 		unlinkNodesBetween(p, q)
 		return
 	}
-	if q.startOffset <= interval.stopOffset {
+	if q.StartOffset <= interval.stopOffset {
 		// merge new interval into q
-		q.startOffset = interval.startOffset
+		q.StartOffset = interval.StartOffset
 		unlinkNodesBetween(p, q)
 		return
 	}

weed/filesys/page_writer/chunked_file_writer.go

@@ -64,7 +64,7 @@ func (cw *ChunkedFileWriter) ReadDataAt(p []byte, off int64) (maxStop int64) {
 	actualChunkIndex, chunkUsage := cw.toActualReadOffset(off)
 	if chunkUsage != nil {
 		for t := chunkUsage.head.next; t != chunkUsage.tail; t = t.next {
-			logicStart := max(off, logicChunkIndex*cw.ChunkSize+t.startOffset)
+			logicStart := max(off, logicChunkIndex*cw.ChunkSize+t.StartOffset)
 			logicStop := min(off+int64(len(p)), logicChunkIndex*cw.ChunkSize+t.stopOffset)
 			if logicStart < logicStop {
 				actualStart := logicStart - logicChunkIndex*cw.ChunkSize + int64(actualChunkIndex)*cw.ChunkSize
@@ -110,11 +110,16 @@ func (cw *ChunkedFileWriter) ProcessEachInterval(process func(file *os.File, log
 		}
 	}
 }
-func (cw *ChunkedFileWriter) Destroy() {
+
+// Reset releases used resources
+func (cw *ChunkedFileWriter) Reset() {
 	if cw.file != nil {
 		cw.file.Close()
 		os.Remove(cw.file.Name())
+		cw.file = nil
 	}
+	cw.logicToActualChunkIndex = make(map[LogicChunkIndex]ActualChunkIndex)
+	cw.chunkUsages = cw.chunkUsages[:0]
 }
 
 type FileIntervalReader struct {
@@ -134,7 +139,7 @@ func NewFileIntervalReader(cw *ChunkedFileWriter, logicChunkIndex LogicChunkInde
 	}
 	return &FileIntervalReader{
 		f:           cw.file,
-		startOffset: int64(actualChunkIndex)*cw.ChunkSize + interval.startOffset,
+		startOffset: int64(actualChunkIndex)*cw.ChunkSize + interval.StartOffset,
 		stopOffset:  int64(actualChunkIndex)*cw.ChunkSize + interval.stopOffset,
 		position:    0,
 	}

weed/filesys/page_writer/chunked_file_writer_test.go

@@ -35,9 +35,9 @@ func writeToFile(cw *ChunkedFileWriter, startOffset int64, stopOffset int64) {
 
 func TestWriteChunkedFile(t *testing.T) {
 	x := NewChunkedFileWriter(os.TempDir(), 20)
-	defer x.Destroy()
+	defer x.Reset()
 	y := NewChunkedFileWriter(os.TempDir(), 12)
-	defer y.Destroy()
+	defer y.Reset()
 
 	batchSize := 4
 	buf := make([]byte, batchSize)

weed/filesys/page_writer/chunked_stream_writer.go

@@ -0,0 +1,119 @@
+package page_writer
+
+import (
+	"github.com/chrislusf/seaweedfs/weed/util"
+	"github.com/chrislusf/seaweedfs/weed/util/mem"
+	"io"
+	"sync"
+	"sync/atomic"
+)
+
+type SaveToStorageFunc func(reader io.Reader, offset int64, size int64, cleanupFn func())
+
+// ChunkedStreamWriter assumes the write requests will come in within chunks and in streaming mode
+type ChunkedStreamWriter struct {
+	activeChunks     map[LogicChunkIndex]*MemChunk
+	activeChunksLock sync.Mutex
+	ChunkSize        int64
+	saveToStorageFn  SaveToStorageFunc
+	sync.Mutex
+}
+
+type MemChunk struct {
+	buf   []byte
+	usage *ChunkWrittenIntervalList
+}
+
+var _ = io.WriterAt(&ChunkedStreamWriter{})
+
+func NewChunkedStreamWriter(chunkSize int64) *ChunkedStreamWriter {
+	return &ChunkedStreamWriter{
+		ChunkSize:    chunkSize,
+		activeChunks: make(map[LogicChunkIndex]*MemChunk),
+	}
+}
+
+func (cw *ChunkedStreamWriter) SetSaveToStorageFunction(saveToStorageFn SaveToStorageFunc) {
+	cw.saveToStorageFn = saveToStorageFn
+}
+
+func (cw *ChunkedStreamWriter) WriteAt(p []byte, off int64) (n int, err error) {
+	cw.Lock()
+	defer cw.Unlock()
+
+	logicChunkIndex := LogicChunkIndex(off / cw.ChunkSize)
+	offsetRemainder := off % cw.ChunkSize
+
+	memChunk, found := cw.activeChunks[logicChunkIndex]
+	if !found {
+		memChunk = &MemChunk{
+			buf:   mem.Allocate(int(cw.ChunkSize)),
+			usage: newChunkWrittenIntervalList(),
+		}
+		cw.activeChunks[logicChunkIndex] = memChunk
+	}
+	n = copy(memChunk.buf[offsetRemainder:], p)
+	memChunk.usage.MarkWritten(offsetRemainder, offsetRemainder+int64(n))
+	if memChunk.usage.IsComplete(cw.ChunkSize) {
+		if cw.saveToStorageFn != nil {
+			cw.saveOneChunk(memChunk, logicChunkIndex)
+			delete(cw.activeChunks, logicChunkIndex)
+		}
+	}
+
+	return
+}
+
+func (cw *ChunkedStreamWriter) ReadDataAt(p []byte, off int64) (maxStop int64) {
+	cw.Lock()
+	defer cw.Unlock()
+
+	logicChunkIndex := LogicChunkIndex(off / cw.ChunkSize)
+	memChunkBaseOffset := int64(logicChunkIndex) * cw.ChunkSize
+	memChunk, found := cw.activeChunks[logicChunkIndex]
+	if !found {
+		return
+	}
+
+	for t := memChunk.usage.head.next; t != memChunk.usage.tail; t = t.next {
+		logicStart := max(off, int64(logicChunkIndex)*cw.ChunkSize+t.StartOffset)
+		logicStop := min(off+int64(len(p)), memChunkBaseOffset+t.stopOffset)
+		if logicStart < logicStop {
+			copy(p[logicStart-off:logicStop-off], memChunk.buf[logicStart-memChunkBaseOffset:logicStop-memChunkBaseOffset])
+			maxStop = max(maxStop, logicStop)
+		}
+	}
+	return
+}
+
+func (cw *ChunkedStreamWriter) FlushAll() {
+	cw.Lock()
+	defer cw.Unlock()
+	for logicChunkIndex, memChunk := range cw.activeChunks {
+		if cw.saveToStorageFn != nil {
+			cw.saveOneChunk(memChunk, logicChunkIndex)
+			delete(cw.activeChunks, logicChunkIndex)
+		}
+	}
+}
+
+func (cw *ChunkedStreamWriter) saveOneChunk(memChunk *MemChunk, logicChunkIndex LogicChunkIndex) {
+	var referenceCounter = int32(memChunk.usage.size())
+	for t := memChunk.usage.head.next; t != memChunk.usage.tail; t = t.next {
+		reader := util.NewBytesReader(memChunk.buf[t.StartOffset:t.stopOffset])
+		cw.saveToStorageFn(reader, int64(logicChunkIndex)*cw.ChunkSize+t.StartOffset, t.Size(), func() {
+			atomic.AddInt32(&referenceCounter, -1)
+			if atomic.LoadInt32(&referenceCounter) == 0 {
+				mem.Free(memChunk.buf)
+			}
+		})
+	}
+}
+
+// Reset releases used resources
+func (cw *ChunkedStreamWriter) Reset() {
+	for t, memChunk := range cw.activeChunks {
+		mem.Free(memChunk.buf)
+		delete(cw.activeChunks, t)
+	}
+}

weed/filesys/page_writer/chunked_stream_writer_test.go

@@ -0,0 +1,33 @@
+package page_writer
+
+import (
+	"github.com/stretchr/testify/assert"
+	"os"
+	"testing"
+)
+
+func TestWriteChunkedStream(t *testing.T) {
+	x := NewChunkedStreamWriter(20)
+	defer x.Reset()
+	y := NewChunkedFileWriter(os.TempDir(), 12)
+	defer y.Reset()
+
+	batchSize := 4
+	buf := make([]byte, batchSize)
+	for i := 0; i < 256; i++ {
+		for x := 0; x < batchSize; x++ {
+			buf[x] = byte(i)
+		}
+		x.WriteAt(buf, int64(i*batchSize))
+		y.WriteAt(buf, int64((255-i)*batchSize))
+	}
+
+	a := make([]byte, 1)
+	b := make([]byte, 1)
+	for i := 0; i < 256*batchSize; i++ {
+		x.ReadDataAt(a, int64(i))
+		y.ReadDataAt(b, int64(256*batchSize-1-i))
+		assert.Equal(t, a[0], b[0], "same read")
+	}
+
+}

weed/filesys/page_writer_pattern.go

@@ -4,19 +4,17 @@ type WriterPattern struct {
 	isStreaming     bool
 	lastWriteOffset int64
 	chunkSize       int64
-	fileName        string
 }
 
 // For streaming write: only cache the first chunk
 // For random write: fall back to temp file approach
 // writes can only change from streaming mode to non-streaming mode
 
-func NewWriterPattern(fileName string, chunkSize int64) *WriterPattern {
+func NewWriterPattern(chunkSize int64) *WriterPattern {
 	return &WriterPattern{
 		isStreaming:     true,
 		lastWriteOffset: -1,
 		chunkSize:       chunkSize,
-		fileName:        fileName,
 	}
 }
 
@@ -39,3 +37,8 @@ func (rp *WriterPattern) IsStreamingMode() bool {
 func (rp *WriterPattern) IsRandomMode() bool {
 	return !rp.isStreaming
 }
+
+func (rp *WriterPattern) Reset() {
+	rp.isStreaming = true
+	rp.lastWriteOffset = -1
+}