Merge pull request #3955 from MichaelEischer/async-futurefile-completion

Improve archiver performance for small files

changelog/unreleased/pull-3955

@@ -0,0 +1,9 @@
+Enhancement: Improve backup performance for small files
+
+When backing up small files restic was slower than it could be. In particular
+this affected backups using maximum compression.
+
+This has been fixed by reworking the internal parallelism of the backup
+command.
+
+https://github.com/restic/restic/issues/3955

internal/archiver/archiver.go

@@ -68,6 +68,9 @@ type Archiver struct {
 	// be in the snapshot after saving. s contains some statistics about this
 	// particular file/dir.
 	//
+	// Once reading a file has completed successfully (but not saving it yet),
+	// CompleteItem will be called with current == nil.
+	//
 	// CompleteItem may be called asynchronously from several different
 	// goroutines!
 	CompleteItem func(item string, previous, current *restic.Node, s ItemStats, d time.Duration)
@@ -431,6 +434,8 @@ func (arch *Archiver) Save(ctx context.Context, snPath, target string, previous
 		// Save will close the file, we don't need to do that
 		fn = arch.fileSaver.Save(ctx, snPath, target, file, fi, func() {
 			arch.StartFile(snPath)
+		}, func() {
+			arch.CompleteItem(snPath, nil, nil, ItemStats{}, 0)
 		}, func(node *restic.Node, stats ItemStats) {
 			arch.CompleteItem(snPath, previous, node, stats, time.Since(start))
 		})

internal/archiver/archiver_test.go

@@ -53,6 +53,8 @@ func saveFile(t testing.TB, repo restic.Repository, filename string, filesystem
 	}
 
 	var (
+		completeReadingCallback bool
+
 		completeCallbackNode  *restic.Node
 		completeCallbackStats ItemStats
 		completeCallback      bool
@@ -60,6 +62,13 @@ func saveFile(t testing.TB, repo restic.Repository, filename string, filesystem
 		startCallback bool
 	)
 
+	completeReading := func() {
+		completeReadingCallback = true
+		if completeCallback {
+			t.Error("callbacks called in wrong order")
+		}
+	}
+
 	complete := func(node *restic.Node, stats ItemStats) {
 		completeCallback = true
 		completeCallbackNode = node
@@ -80,7 +89,7 @@ func saveFile(t testing.TB, repo restic.Repository, filename string, filesystem
 		t.Fatal(err)
 	}
 
-	res := arch.fileSaver.Save(ctx, "/", filename, file, fi, start, complete)
+	res := arch.fileSaver.Save(ctx, "/", filename, file, fi, start, completeReading, complete)
 
 	fnr := res.take(ctx)
 	if fnr.err != nil {
@@ -101,6 +110,10 @@ func saveFile(t testing.TB, repo restic.Repository, filename string, filesystem
 		t.Errorf("start callback did not happen")
 	}
 
+	if !completeReadingCallback {
+		t.Errorf("completeReading callback did not happen")
+	}
+
 	if !completeCallback {
 		t.Errorf("complete callback did not happen")
 	}

internal/archiver/blob_saver.go

@@ -43,51 +43,18 @@ func (s *BlobSaver) TriggerShutdown() {
 
 // Save stores a blob in the repo. It checks the index and the known blobs
 // before saving anything. It takes ownership of the buffer passed in.
-func (s *BlobSaver) Save(ctx context.Context, t restic.BlobType, buf *Buffer) FutureBlob {
-	ch := make(chan SaveBlobResponse, 1)
+func (s *BlobSaver) Save(ctx context.Context, t restic.BlobType, buf *Buffer, cb func(res SaveBlobResponse)) {
 	select {
-	case s.ch <- saveBlobJob{BlobType: t, buf: buf, ch: ch}:
+	case s.ch <- saveBlobJob{BlobType: t, buf: buf, cb: cb}:
 	case <-ctx.Done():
 		debug.Log("not sending job, context is cancelled")
-		close(ch)
-		return FutureBlob{ch: ch}
 	}
-
-	return FutureBlob{ch: ch}
-}
-
-// FutureBlob is returned by SaveBlob and will return the data once it has been processed.
-type FutureBlob struct {
-	ch <-chan SaveBlobResponse
-}
-
-func (s *FutureBlob) Poll() *SaveBlobResponse {
-	select {
-	case res, ok := <-s.ch:
-		if ok {
-			return &res
-		}
-	default:
-	}
-	return nil
-}
-
-// Take blocks until the result is available or the context is cancelled.
-func (s *FutureBlob) Take(ctx context.Context) SaveBlobResponse {
-	select {
-	case res, ok := <-s.ch:
-		if ok {
-			return res
-		}
-	case <-ctx.Done():
-	}
-	return SaveBlobResponse{}
 }
 
 type saveBlobJob struct {
 	restic.BlobType
 	buf *Buffer
-	ch  chan<- SaveBlobResponse
+	cb  func(res SaveBlobResponse)
 }
 
 type SaveBlobResponse struct {
@@ -128,11 +95,9 @@ func (s *BlobSaver) worker(ctx context.Context, jobs <-chan saveBlobJob) error {
 		res, err := s.saveBlob(ctx, job.BlobType, job.buf.Data)
 		if err != nil {
 			debug.Log("saveBlob returned error, exiting: %v", err)
-			close(job.ch)
 			return err
 		}
-		job.ch <- res
-		close(job.ch)
+		job.cb(res)
 		job.buf.Release()
 	}
 }

internal/archiver/blob_saver_test.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"fmt"
 	"runtime"
+	"sync"
 	"sync/atomic"
 	"testing"
 
@@ -45,16 +46,22 @@ func TestBlobSaver(t *testing.T) {
 
 	b := NewBlobSaver(ctx, wg, saver, uint(runtime.NumCPU()))
 
-	var results []FutureBlob
+	var wait sync.WaitGroup
+	var results []SaveBlobResponse
 
+	wait.Add(20)
 	for i := 0; i < 20; i++ {
 		buf := &Buffer{Data: []byte(fmt.Sprintf("foo%d", i))}
-		fb := b.Save(ctx, restic.DataBlob, buf)
-		results = append(results, fb)
+		idx := i
+		results = append(results, SaveBlobResponse{})
+		b.Save(ctx, restic.DataBlob, buf, func(res SaveBlobResponse) {
+			results[idx] = res
+			wait.Done()
+		})
 	}
 
-	for i, blob := range results {
-		sbr := blob.Take(ctx)
+	wait.Wait()
+	for i, sbr := range results {
 		if sbr.known {
 			t.Errorf("blob %v is known, that should not be the case", i)
 		}
@@ -94,7 +101,7 @@ func TestBlobSaverError(t *testing.T) {
 
 			for i := 0; i < test.blobs; i++ {
 				buf := &Buffer{Data: []byte(fmt.Sprintf("foo%d", i))}
-				b.Save(ctx, restic.DataBlob, buf)
+				b.Save(ctx, restic.DataBlob, buf, func(res SaveBlobResponse) {})
 			}
 
 			b.TriggerShutdown()

internal/archiver/file_saver.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"io"
 	"os"
+	"sync"
 
 	"github.com/restic/chunker"
 	"github.com/restic/restic/internal/debug"
@@ -14,7 +15,7 @@ import (
 )
 
 // SaveBlobFn saves a blob to a repo.
-type SaveBlobFn func(context.Context, restic.BlobType, *Buffer) FutureBlob
+type SaveBlobFn func(context.Context, restic.BlobType, *Buffer, func(res SaveBlobResponse))
 
 // FileSaver concurrently saves incoming files to the repo.
 type FileSaver struct {
@@ -66,17 +67,21 @@ func (s *FileSaver) TriggerShutdown() {
 type CompleteFunc func(*restic.Node, ItemStats)
 
 // Save stores the file f and returns the data once it has been completed. The
-// file is closed by Save.
-func (s *FileSaver) Save(ctx context.Context, snPath string, target string, file fs.File, fi os.FileInfo, start func(), complete CompleteFunc) FutureNode {
+// file is closed by Save. completeReading is only called if the file was read
+// successfully. complete is always called. If completeReading is called, then
+// this will always happen before calling complete.
+func (s *FileSaver) Save(ctx context.Context, snPath string, target string, file fs.File, fi os.FileInfo, start func(), completeReading func(), complete CompleteFunc) FutureNode {
 	fn, ch := newFutureNode()
 	job := saveFileJob{
-		snPath:   snPath,
-		target:   target,
-		file:     file,
-		fi:       fi,
-		start:    start,
-		complete: complete,
-		ch:       ch,
+		snPath: snPath,
+		target: target,
+		file:   file,
+		fi:     fi,
+		ch:     ch,
+
+		start:           start,
+		completeReading: completeReading,
+		complete:        complete,
 	}
 
 	select {
@@ -91,56 +96,79 @@ func (s *FileSaver) Save(ctx context.Context, snPath string, target string, file
 }
 
 type saveFileJob struct {
-	snPath   string
-	target   string
-	file     fs.File
-	fi       os.FileInfo
-	ch       chan<- futureNodeResult
-	complete CompleteFunc
-	start    func()
+	snPath string
+	target string
+	file   fs.File
+	fi     os.FileInfo
+	ch     chan<- futureNodeResult
+
+	start           func()
+	completeReading func()
+	complete        CompleteFunc
 }
 
 // saveFile stores the file f in the repo, then closes it.
-func (s *FileSaver) saveFile(ctx context.Context, chnker *chunker.Chunker, snPath string, target string, f fs.File, fi os.FileInfo, start func()) futureNodeResult {
+func (s *FileSaver) saveFile(ctx context.Context, chnker *chunker.Chunker, snPath string, target string, f fs.File, fi os.FileInfo, start func(), finishReading func(), finish func(res futureNodeResult)) {
 	start()
 
-	stats := ItemStats{}
 	fnr := futureNodeResult{
 		snPath: snPath,
 		target: target,
 	}
+	var lock sync.Mutex
+	remaining := 0
+	isCompleted := false
+
+	completeBlob := func() {
+		lock.Lock()
+		defer lock.Unlock()
+
+		remaining--
+		if remaining == 0 && fnr.err == nil {
+			if isCompleted {
+				panic("completed twice")
+			}
+			isCompleted = true
+			finish(fnr)
+		}
+	}
+	completeError := func(err error) {
+		lock.Lock()
+		defer lock.Unlock()
+
+		if fnr.err == nil {
+			if isCompleted {
+				panic("completed twice")
+			}
+			isCompleted = true
+			fnr.err = err
+			fnr.node = nil
+			fnr.stats = ItemStats{}
+			finish(fnr)
+		}
+	}
 
 	debug.Log("%v", snPath)
 
 	node, err := s.NodeFromFileInfo(snPath, f.Name(), fi)
 	if err != nil {
 		_ = f.Close()
-		fnr.err = err
-		return fnr
+		completeError(err)
+		return
 	}
 
 	if node.Type != "file" {
 		_ = f.Close()
-		fnr.err = errors.Errorf("node type %q is wrong", node.Type)
-		return fnr
+		completeError(errors.Errorf("node type %q is wrong", node.Type))
+		return
 	}
 
 	// reuse the chunker
 	chnker.Reset(f, s.pol)
 
-	var results []FutureBlob
-	complete := func(sbr SaveBlobResponse) {
-		if !sbr.known {
-			stats.DataBlobs++
-			stats.DataSize += uint64(sbr.length)
-			stats.DataSizeInRepo += uint64(sbr.sizeInRepo)
-		}
-
-		node.Content = append(node.Content, sbr.id)
-	}
-
 	node.Content = []restic.ID{}
-	var size uint64
+	node.Size = 0
+	var idx int
 	for {
 		buf := s.saveFilePool.Get()
 		chunk, err := chnker.Next(buf.Data)
@@ -150,62 +178,63 @@ func (s *FileSaver) saveFile(ctx context.Context, chnker *chunker.Chunker, snPat
 		}
 
 		buf.Data = chunk.Data
-
-		size += uint64(chunk.Length)
+		node.Size += uint64(chunk.Length)
 
 		if err != nil {
 			_ = f.Close()
-			fnr.err = err
-			return fnr
+			completeError(err)
+			return
 		}
+		// test if the context has been cancelled, return the error
+		if ctx.Err() != nil {
+			_ = f.Close()
+			completeError(ctx.Err())
+			return
+		}
+
+		// add a place to store the saveBlob result
+		pos := idx
+		node.Content = append(node.Content, restic.ID{})
+
+		s.saveBlob(ctx, restic.DataBlob, buf, func(sbr SaveBlobResponse) {
+			lock.Lock()
+			if !sbr.known {
+				fnr.stats.DataBlobs++
+				fnr.stats.DataSize += uint64(sbr.length)
+				fnr.stats.DataSizeInRepo += uint64(sbr.sizeInRepo)
+			}
+
+			node.Content[pos] = sbr.id
+			lock.Unlock()
+
+			completeBlob()
+		})
+		idx++
 
 		// test if the context has been cancelled, return the error
 		if ctx.Err() != nil {
 			_ = f.Close()
-			fnr.err = ctx.Err()
-			return fnr
-		}
-
-		res := s.saveBlob(ctx, restic.DataBlob, buf)
-		results = append(results, res)
-
-		// test if the context has been cancelled, return the error
-		if ctx.Err() != nil {
-			_ = f.Close()
-			fnr.err = ctx.Err()
-			return fnr
+			completeError(ctx.Err())
+			return
 		}
 
 		s.CompleteBlob(uint64(len(chunk.Data)))
-
-		// collect already completed blobs
-		for len(results) > 0 {
-			sbr := results[0].Poll()
-			if sbr == nil {
-				break
-			}
-			results[0] = FutureBlob{}
-			results = results[1:]
-			complete(*sbr)
-		}
 	}
 
 	err = f.Close()
 	if err != nil {
-		fnr.err = err
-		return fnr
+		completeError(err)
+		return
 	}
 
-	for i, res := range results {
-		results[i] = FutureBlob{}
-		sbr := res.Take(ctx)
-		complete(sbr)
-	}
-
-	node.Size = size
 	fnr.node = node
-	fnr.stats = stats
-	return fnr
+	lock.Lock()
+	// require one additional completeFuture() call to ensure that the future only completes
+	// after reaching the end of this method
+	remaining += idx + 1
+	lock.Unlock()
+	finishReading()
+	completeBlob()
 }
 
 func (s *FileSaver) worker(ctx context.Context, jobs <-chan saveFileJob) {
@@ -224,11 +253,16 @@ func (s *FileSaver) worker(ctx context.Context, jobs <-chan saveFileJob) {
 			}
 		}
 
-		res := s.saveFile(ctx, chnker, job.snPath, job.target, job.file, job.fi, job.start)
-		if job.complete != nil {
-			job.complete(res.node, res.stats)
-		}
-		job.ch <- res
-		close(job.ch)
+		s.saveFile(ctx, chnker, job.snPath, job.target, job.file, job.fi, job.start, func() {
+			if job.completeReading != nil {
+				job.completeReading()
+			}
+		}, func(res futureNodeResult) {
+			if job.complete != nil {
+				job.complete(res.node, res.stats)
+			}
+			job.ch <- res
+			close(job.ch)
+		})
 	}
 }

internal/archiver/file_saver_test.go

@@ -34,10 +34,8 @@ func createTestFiles(t testing.TB, num int) (files []string, cleanup func()) {
 func startFileSaver(ctx context.Context, t testing.TB) (*FileSaver, context.Context, *errgroup.Group) {
 	wg, ctx := errgroup.WithContext(ctx)
 
-	saveBlob := func(ctx context.Context, tpe restic.BlobType, buf *Buffer) FutureBlob {
-		ch := make(chan SaveBlobResponse)
-		close(ch)
-		return FutureBlob{ch: ch}
+	saveBlob := func(ctx context.Context, tpe restic.BlobType, buf *Buffer, cb func(SaveBlobResponse)) {
+		cb(SaveBlobResponse{})
 	}
 
 	workers := uint(runtime.NumCPU())
@@ -62,6 +60,7 @@ func TestFileSaver(t *testing.T) {
 	defer cleanup()
 
 	startFn := func() {}
+	completeReadingFn := func() {}
 	completeFn := func(*restic.Node, ItemStats) {}
 
 	testFs := fs.Local{}
@@ -80,7 +79,7 @@ func TestFileSaver(t *testing.T) {
 			t.Fatal(err)
 		}
 
-		ff := s.Save(ctx, filename, filename, f, fi, startFn, completeFn)
+		ff := s.Save(ctx, filename, filename, f, fi, startFn, completeReadingFn, completeFn)
 		results = append(results, ff)
 	}
 

internal/archiver/tree_saver.go

@@ -11,7 +11,7 @@ import (
 
 // TreeSaver concurrently saves incoming trees to the repo.
 type TreeSaver struct {
-	saveBlob func(ctx context.Context, t restic.BlobType, buf *Buffer) FutureBlob
+	saveBlob func(ctx context.Context, t restic.BlobType, buf *Buffer, cb func(res SaveBlobResponse))
 	errFn    ErrorFunc
 
 	ch chan<- saveTreeJob
@@ -19,7 +19,7 @@ type TreeSaver struct {
 
 // NewTreeSaver returns a new tree saver. A worker pool with treeWorkers is
 // started, it is stopped when ctx is cancelled.
-func NewTreeSaver(ctx context.Context, wg *errgroup.Group, treeWorkers uint, saveBlob func(ctx context.Context, t restic.BlobType, buf *Buffer) FutureBlob, errFn ErrorFunc) *TreeSaver {
+func NewTreeSaver(ctx context.Context, wg *errgroup.Group, treeWorkers uint, saveBlob func(ctx context.Context, t restic.BlobType, buf *Buffer, cb func(res SaveBlobResponse)), errFn ErrorFunc) *TreeSaver {
 	ch := make(chan saveTreeJob)
 
 	s := &TreeSaver{
@@ -124,21 +124,24 @@ func (s *TreeSaver) save(ctx context.Context, job *saveTreeJob) (*restic.Node, I
 	}
 
 	b := &Buffer{Data: buf}
-	res := s.saveBlob(ctx, restic.TreeBlob, b)
+	ch := make(chan SaveBlobResponse, 1)
+	s.saveBlob(ctx, restic.TreeBlob, b, func(res SaveBlobResponse) {
+		ch <- res
+	})
 
-	sbr := res.Take(ctx)
-	if !sbr.known {
-		stats.TreeBlobs++
-		stats.TreeSize += uint64(sbr.length)
-		stats.TreeSizeInRepo += uint64(sbr.sizeInRepo)
-	}
-	// The context was canceled in the meantime, id might be invalid
-	if ctx.Err() != nil {
+	select {
+	case sbr := <-ch:
+		if !sbr.known {
+			stats.TreeBlobs++
+			stats.TreeSize += uint64(sbr.length)
+			stats.TreeSizeInRepo += uint64(sbr.sizeInRepo)
+		}
+
+		node.Subtree = &sbr.id
+		return node, stats, nil
+	case <-ctx.Done():
 		return nil, stats, ctx.Err()
 	}
-
-	node.Subtree = &sbr.id
-	return node, stats, nil
 }
 
 func (s *TreeSaver) worker(ctx context.Context, jobs <-chan saveTreeJob) error {

internal/archiver/tree_saver_test.go

@@ -12,15 +12,13 @@ import (
 	"golang.org/x/sync/errgroup"
 )
 
-func treeSaveHelper(ctx context.Context, t restic.BlobType, buf *Buffer) FutureBlob {
-	ch := make(chan SaveBlobResponse, 1)
-	ch <- SaveBlobResponse{
+func treeSaveHelper(ctx context.Context, t restic.BlobType, buf *Buffer, cb func(res SaveBlobResponse)) {
+	cb(SaveBlobResponse{
 		id:         restic.NewRandomID(),
 		known:      false,
 		length:     len(buf.Data),
 		sizeInRepo: len(buf.Data),
-	}
-	return FutureBlob{ch: ch}
+	})
 }
 
 func setupTreeSaver() (context.Context, context.CancelFunc, *TreeSaver, func() error) {

internal/ui/termstatus/status.go

@@ -25,6 +25,7 @@ type Terminal struct {
 	msg             chan message
 	status          chan status
 	canUpdateStatus bool
+	lastStatusLen   int
 
 	// will be closed when the goroutine which runs Run() terminates, so it'll
 	// yield a default value immediately
@@ -154,6 +155,18 @@ func (t *Terminal) run(ctx context.Context) {
 }
 
 func (t *Terminal) writeStatus(status []string) {
+	statusLen := len(status)
+	status = append([]string{}, status...)
+	for i := len(status); i < t.lastStatusLen; i++ {
+		// clear no longer used status lines
+		status = append(status, "")
+		if i > 0 {
+			// all lines except the last one must have a line break
+			status[i-1] = status[i-1] + "\n"
+		}
+	}
+	t.lastStatusLen = statusLen
+
 	for _, line := range status {
 		t.clearCurrentLine(t.wr, t.fd)