repository: Limit to a single pending pack file

Use only a single not completed pack file to keep the number of open and
active pack files low. The main change here is to defer hashing the pack
file to the upload step. This prevents the pack assembly step to become
a bottleneck as the only task is now to write data to the temporary pack
file.

The tests are cleaned up to no longer reimplement packer manager
functions.

internal/repository/packer_manager.go

@@ -1,9 +1,10 @@
 package repository
 
 import (
+	"bufio"
 	"context"
-	"hash"
 	"io"
+	"io/ioutil"
 	"os"
 	"runtime"
 	"sync"
@@ -23,32 +24,29 @@ import (
 // Packer holds a pack.Packer together with a hash writer.
 type Packer struct {
 	*pack.Packer
-	hw      *hashing.Writer
-	beHw    *hashing.Writer
 	tmpfile *os.File
+	bufWr   *bufio.Writer
 }
 
 // packerManager keeps a list of open packs and creates new on demand.
 type packerManager struct {
-	tpe      restic.BlobType
+	tpe     restic.BlobType
-	key      *crypto.Key
+	key     *crypto.Key
-	hasherFn func() hash.Hash
+	queueFn func(ctx context.Context, t restic.BlobType, p *Packer) error
-	queueFn  func(ctx context.Context, t restic.BlobType, p *Packer) error
 
-	pm      sync.Mutex
+	pm     sync.Mutex
-	packers []*Packer
+	packer *Packer
 }
 
 const minPackSize = 4 * 1024 * 1024
 
 // newPackerManager returns an new packer manager which writes temporary files
 // to a temporary directory
-func newPackerManager(key *crypto.Key, hasherFn func() hash.Hash, tpe restic.BlobType, queueFn func(ctx context.Context, t restic.BlobType, p *Packer) error) *packerManager {
+func newPackerManager(key *crypto.Key, tpe restic.BlobType, queueFn func(ctx context.Context, t restic.BlobType, p *Packer) error) *packerManager {
 	return &packerManager{
-		tpe:      tpe,
+		tpe:     tpe,
-		key:      key,
+		key:     key,
-		hasherFn: hasherFn,
+		queueFn: queueFn,
-		queueFn:  queueFn,
 	}
 }
 
@@ -56,24 +54,34 @@ func (r *packerManager) Flush(ctx context.Context) error {
 	r.pm.Lock()
 	defer r.pm.Unlock()
 
-	debug.Log("manually flushing %d packs", len(r.packers))
+	if r.packer != nil {
-	for _, packer := range r.packers {
+		debug.Log("manually flushing pending pack")
-		err := r.queueFn(ctx, r.tpe, packer)
+		err := r.queueFn(ctx, r.tpe, r.packer)
 		if err != nil {
 			return err
 		}
+		r.packer = nil
 	}
-	r.packers = r.packers[:0]
 	return nil
 }
 
 func (r *packerManager) SaveBlob(ctx context.Context, t restic.BlobType, id restic.ID, ciphertext []byte, uncompressedLength int) (int, error) {
-	packer, err := r.findPacker()
+	r.pm.Lock()
-	if err != nil {
+	defer r.pm.Unlock()
-		return 0, err
+
+	var err error
+	packer := r.packer
+	if r.packer == nil {
+		packer, err = r.newPacker()
+		if err != nil {
+			return 0, err
+		}
 	}
+	// remember packer
+	r.packer = packer
 
 	// save ciphertext
+	// Add only appends bytes in memory to avoid being a scaling bottleneck
 	size, err := packer.Add(t, id, ciphertext, uncompressedLength)
 	if err != nil {
 		return 0, err
@@ -82,10 +90,12 @@ func (r *packerManager) SaveBlob(ctx context.Context, t restic.BlobType, id rest
 	// if the pack is not full enough, put back to the list
 	if packer.Size() < minPackSize {
 		debug.Log("pack is not full enough (%d bytes)", packer.Size())
-		r.insertPacker(packer)
 		return size, nil
 	}
+	// forget full packer
+	r.packer = nil
 
+	// call while holding lock to prevent findPacker from creating new packers if the uploaders are busy
 	// else write the pack to the backend
 	err = r.queueFn(ctx, t, packer)
 	if err != nil {
@@ -97,56 +107,24 @@ func (r *packerManager) SaveBlob(ctx context.Context, t restic.BlobType, id rest
 
 // findPacker returns a packer for a new blob of size bytes. Either a new one is
 // created or one is returned that already has some blobs.
-func (r *packerManager) findPacker() (packer *Packer, err error) {
+func (r *packerManager) newPacker() (packer *Packer, err error) {
-	r.pm.Lock()
-	defer r.pm.Unlock()
-
-	// search for a suitable packer
-	if len(r.packers) > 0 {
-		p := r.packers[0]
-		last := len(r.packers) - 1
-		r.packers[0] = r.packers[last]
-		r.packers[last] = nil // Allow GC of stale reference.
-		r.packers = r.packers[:last]
-		return p, nil
-	}
-
-	// no suitable packer found, return new
 	debug.Log("create new pack")
 	tmpfile, err := fs.TempFile("", "restic-temp-pack-")
 	if err != nil {
 		return nil, errors.Wrap(err, "fs.TempFile")
 	}
 
-	w := io.Writer(tmpfile)
+	bufWr := bufio.NewWriter(tmpfile)
-	beHasher := r.hasherFn()
+	p := pack.NewPacker(r.key, bufWr)
-	var beHw *hashing.Writer
-	if beHasher != nil {
-		beHw = hashing.NewWriter(w, beHasher)
-		w = beHw
-	}
-
-	hw := hashing.NewWriter(w, sha256.New())
-	p := pack.NewPacker(r.key, hw)
 	packer = &Packer{
 		Packer:  p,
-		beHw:    beHw,
-		hw:      hw,
 		tmpfile: tmpfile,
+		bufWr:   bufWr,
 	}
 
 	return packer, nil
 }
 
-// insertPacker appends p to s.packs.
-func (r *packerManager) insertPacker(p *Packer) {
-	r.pm.Lock()
-	defer r.pm.Unlock()
-
-	r.packers = append(r.packers, p)
-	debug.Log("%d packers\n", len(r.packers))
-}
-
 // savePacker stores p in the backend.
 func (r *Repository) savePacker(ctx context.Context, t restic.BlobType, p *Packer) error {
 	debug.Log("save packer for %v with %d blobs (%d bytes)\n", t, p.Packer.Count(), p.Packer.Size())
@@ -154,20 +132,43 @@ func (r *Repository) savePacker(ctx context.Context, t restic.BlobType, p *Packe
 	if err != nil {
 		return err
 	}
-
+	err = p.bufWr.Flush()
-	id := restic.IDFromHash(p.hw.Sum(nil))
-	h := restic.Handle{Type: restic.PackFile, Name: id.String(),
-		ContainedBlobType: t}
-	var beHash []byte
-	if p.beHw != nil {
-		beHash = p.beHw.Sum(nil)
-	}
-	rd, err := restic.NewFileReader(p.tmpfile, beHash)
 	if err != nil {
 		return err
 	}
 
-	err = r.be.Save(ctx, h, rd)
+	// calculate sha256 hash in a second pass
+	var rd io.Reader
+	rd, err = restic.NewFileReader(p.tmpfile, nil)
+	if err != nil {
+		return err
+	}
+	beHasher := r.be.Hasher()
+	var beHr *hashing.Reader
+	if beHasher != nil {
+		beHr = hashing.NewReader(rd, beHasher)
+		rd = beHr
+	}
+
+	hr := hashing.NewReader(rd, sha256.New())
+	_, err = io.Copy(ioutil.Discard, hr)
+	if err != nil {
+		return err
+	}
+
+	id := restic.IDFromHash(hr.Sum(nil))
+	h := restic.Handle{Type: restic.PackFile, Name: id.String(),
+		ContainedBlobType: t}
+	var beHash []byte
+	if beHr != nil {
+		beHash = beHr.Sum(nil)
+	}
+	rrd, err := restic.NewFileReader(p.tmpfile, beHash)
+	if err != nil {
+		return err
+	}
+
+	err = r.be.Save(ctx, h, rrd)
 	if err != nil {
 		debug.Log("Save(%v) error: %v", h, err)
 		return err
@@ -198,11 +199,3 @@ func (r *Repository) savePacker(ctx context.Context, t restic.BlobType, p *Packe
 	}
 	return r.idx.SaveFullIndex(ctx, r)
 }
-
-// countPacker returns the number of open (unfinished) packers.
-func (r *packerManager) countPacker() int {
-	r.pm.Lock()
-	defer r.pm.Unlock()
-
-	return len(r.packers)
-}

internal/repository/packer_manager_test.go

@@ -2,26 +2,16 @@ package repository
 
 import (
 	"context"
-	"hash"
 	"io"
 	"math/rand"
-	"os"
 	"sync"
 	"testing"
 
-	"github.com/restic/restic/internal/backend/mem"
 	"github.com/restic/restic/internal/crypto"
-	"github.com/restic/restic/internal/fs"
-	"github.com/restic/restic/internal/mock"
 	"github.com/restic/restic/internal/restic"
+	"github.com/restic/restic/internal/test"
 )
 
-// Saver implements saving data in a backend.
-type Saver interface {
-	Save(context.Context, restic.Handle, restic.RewindReader) error
-	Hasher() hash.Hash
-}
-
 func randomID(rd io.Reader) restic.ID {
 	id := restic.ID{}
 	_, err := io.ReadFull(rd, id[:])
@@ -40,91 +30,27 @@ func min(a, b int) int {
 	return b
 }
 
-func saveFile(t testing.TB, be Saver, length int, f *os.File, id restic.ID, hash []byte) {
+func fillPacks(t testing.TB, rnd *rand.Rand, pm *packerManager, buf []byte) (bytes int) {
-	h := restic.Handle{Type: restic.PackFile, Name: id.String()}
-	t.Logf("save file %v", h)
-
-	rd, err := restic.NewFileReader(f, hash)
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	err = be.Save(context.TODO(), h, rd)
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	if err := f.Close(); err != nil {
-		t.Fatal(err)
-	}
-
-	if err := fs.RemoveIfExists(f.Name()); err != nil {
-		t.Fatal(err)
-	}
-}
-
-func fillPacks(t testing.TB, rnd *rand.Rand, be Saver, pm *packerManager, buf []byte) (bytes int) {
 	for i := 0; i < 100; i++ {
 		l := rnd.Intn(maxBlobSize)
-
-		packer, err := pm.findPacker()
-		if err != nil {
-			t.Fatal(err)
-		}
-
 		id := randomID(rnd)
 		buf = buf[:l]
 		// Only change a few bytes so we know we're not benchmarking the RNG.
 		rnd.Read(buf[:min(l, 4)])
 
-		n, err := packer.Add(restic.DataBlob, id, buf, 0)
+		n, err := pm.SaveBlob(context.TODO(), restic.DataBlob, id, buf, 0)
 		if err != nil {
 			t.Fatal(err)
 		}
-		if n != l+37 {
+		if n != l+37 && n != l+37+36 {
 			t.Errorf("Add() returned invalid number of bytes: want %v, got %v", l, n)
 		}
-		bytes += l
+		bytes += n
-
-		if packer.Size() < minPackSize {
-			pm.insertPacker(packer)
-			continue
-		}
-
-		err = packer.Finalize()
-		if err != nil {
-			t.Fatal(err)
-		}
-
-		packID := restic.IDFromHash(packer.hw.Sum(nil))
-		var beHash []byte
-		if packer.beHw != nil {
-			beHash = packer.beHw.Sum(nil)
-		}
-		saveFile(t, be, int(packer.Size()), packer.tmpfile, packID, beHash)
 	}
-
+	err := pm.Flush(context.TODO())
-	return bytes
+	if err != nil {
-}
+		t.Fatal(err)
-
-func flushRemainingPacks(t testing.TB, be Saver, pm *packerManager) (bytes int) {
-	if pm.countPacker() > 0 {
-		for _, packer := range pm.packers {
-			err := packer.Finalize()
-			if err != nil {
-				t.Fatal(err)
-			}
-			bytes += packer.HeaderOverhead()
-
-			packID := restic.IDFromHash(packer.hw.Sum(nil))
-			var beHash []byte
-			if packer.beHw != nil {
-				beHash = packer.beHw.Sum(nil)
-			}
-			saveFile(t, be, int(packer.Size()), packer.tmpfile, packID, beHash)
-		}
 	}
-
 	return bytes
 }
 
@@ -143,13 +69,21 @@ func TestPackerManager(t *testing.T) {
 func testPackerManager(t testing.TB) int64 {
 	rnd := rand.New(rand.NewSource(randomSeed))
 
-	be := mem.New()
+	savedBytes := int(0)
-	pm := newPackerManager(crypto.NewRandomKey(), be.Hasher, restic.DataBlob, nil)
+	pm := newPackerManager(crypto.NewRandomKey(), restic.DataBlob, func(ctx context.Context, tp restic.BlobType, p *Packer) error {
+		err := p.Finalize()
+		if err != nil {
+			return err
+		}
+		savedBytes += int(p.Size())
+		return nil
+	})
 
 	blobBuf := make([]byte, maxBlobSize)
 
-	bytes := fillPacks(t, rnd, be, pm, blobBuf)
+	bytes := fillPacks(t, rnd, pm, blobBuf)
-	bytes += flushRemainingPacks(t, be, pm)
+	// bytes does not include the last packs header
+	test.Equals(t, savedBytes, bytes+36)
 
 	t.Logf("saved %d bytes", bytes)
 	return int64(bytes)
@@ -162,10 +96,6 @@ func BenchmarkPackerManager(t *testing.B) {
 	})
 
 	rnd := rand.New(rand.NewSource(randomSeed))
-
-	be := &mock.Backend{
-		SaveFn: func(context.Context, restic.Handle, restic.RewindReader) error { return nil },
-	}
 	blobBuf := make([]byte, maxBlobSize)
 
 	t.ReportAllocs()
@@ -174,8 +104,9 @@ func BenchmarkPackerManager(t *testing.B) {
 
 	for i := 0; i < t.N; i++ {
 		rnd.Seed(randomSeed)
-		pm := newPackerManager(crypto.NewRandomKey(), be.Hasher, restic.DataBlob, nil)
+		pm := newPackerManager(crypto.NewRandomKey(), restic.DataBlob, func(ctx context.Context, t restic.BlobType, p *Packer) error {
-		fillPacks(t, rnd, be, pm, blobBuf)
+			return nil
-		flushRemainingPacks(t, be, pm)
+		})
+		fillPacks(t, rnd, pm, blobBuf)
 	}
 }

internal/repository/repository.go

@@ -520,8 +520,8 @@ func (r *Repository) StartPackUploader(ctx context.Context, wg *errgroup.Group)
 	innerWg, ctx := errgroup.WithContext(ctx)
 	r.packerWg = innerWg
 	r.uploader = newPackerUploader(ctx, innerWg, r, r.be.Connections())
-	r.treePM = newPackerManager(r.key, r.be.Hasher, restic.TreeBlob, r.uploader.QueuePacker)
+	r.treePM = newPackerManager(r.key, restic.TreeBlob, r.uploader.QueuePacker)
-	r.dataPM = newPackerManager(r.key, r.be.Hasher, restic.DataBlob, r.uploader.QueuePacker)
+	r.dataPM = newPackerManager(r.key, restic.DataBlob, r.uploader.QueuePacker)
 
 	wg.Go(func() error {
 		return innerWg.Wait()