Optimize Repository.ListPack()

Use pack file size returned by Backend.List() to avoid extra per-pack
Backend.Stat() requests

Signed-off-by: Igor Fedorenko <igor@ifedorenko.com>

changelog/0.8.2/pull-1575

@@ -0,0 +1,7 @@
+Enhancement: Reduce number of remote requests during Repository.ListPack()
+
+This change eliminates redundant remote repository calls and improves 
+repository reindex and purge time.
+
+https://github.com/restic/restic/issues/1567
+https://github.com/restic/restic/pull/1575

internal/index/index.go

@@ -49,23 +49,21 @@ func New(ctx context.Context, repo restic.Repository, ignorePacks restic.IDSet,
 	for job := range ch {
 		p.Report(restic.Stat{Blobs: 1})
 
-		packID := job.Data.(restic.ID)
+		j := job.Result.(list.Result)
 		if job.Error != nil {
 			cause := errors.Cause(job.Error)
 			if _, ok := cause.(pack.InvalidFileError); ok {
-				invalidFiles = append(invalidFiles, packID)
+				invalidFiles = append(invalidFiles, j.PackID())
 				continue
 			}
 
-			fmt.Fprintf(os.Stderr, "pack file cannot be listed %v: %v\n", packID.Str(), job.Error)
+			fmt.Fprintf(os.Stderr, "pack file cannot be listed %v: %v\n", j.PackID(), job.Error)
 			continue
 		}
 
-		j := job.Result.(list.Result)
+		debug.Log("pack %v contains %d blobs", j.PackID(), len(j.Entries()))
 
-		debug.Log("pack %v contains %d blobs", packID.Str(), len(j.Entries()))
-
-		err := idx.AddPack(packID, j.Size(), j.Entries())
+		err := idx.AddPack(j.PackID(), j.Size(), j.Entries())
 		if err != nil {
 			return nil, nil, err
 		}

internal/list/list.go

@@ -12,7 +12,7 @@ const listPackWorkers = 10
 // Lister combines lists packs in a repo and blobs in a pack.
 type Lister interface {
 	List(context.Context, restic.FileType, func(restic.ID, int64) error) error
-	ListPack(context.Context, restic.ID) ([]restic.Blob, int64, error)
+	ListPack(context.Context, restic.ID, int64) ([]restic.Blob, int64, error)
 }
 
 // Result is returned in the channel from LoadBlobsFromAllPacks.
@@ -39,12 +39,17 @@ func (l Result) Entries() []restic.Blob {
 
 // AllPacks sends the contents of all packs to ch.
 func AllPacks(ctx context.Context, repo Lister, ignorePacks restic.IDSet, ch chan<- worker.Job) {
+	type fileInfo struct {
+		id   restic.ID
+		size int64
+	}
+
 	f := func(ctx context.Context, job worker.Job) (interface{}, error) {
-		packID := job.Data.(restic.ID)
-		entries, size, err := repo.ListPack(ctx, packID)
+		packInfo := job.Data.(fileInfo)
+		entries, size, err := repo.ListPack(ctx, packInfo.id, packInfo.size)
 
 		return Result{
-			packID:  packID,
+			packID:  packInfo.id,
 			size:    size,
 			entries: entries,
 		}, err
@@ -62,7 +67,7 @@ func AllPacks(ctx context.Context, repo Lister, ignorePacks restic.IDSet, ch cha
 			}
 
 			select {
-			case jobCh <- worker.Job{Data: id}:
+			case jobCh <- worker.Job{Data: fileInfo{id: id, size: size}, Result: Result{packID: id}}:
 			case <-ctx.Done():
 				return ctx.Err()
 			}

internal/repository/repack_test.go

@@ -75,7 +75,7 @@ func selectBlobs(t *testing.T, repo restic.Repository, p float32) (list1, list2
 	blobs := restic.NewBlobSet()
 
 	err := repo.List(context.TODO(), restic.DataFile, func(id restic.ID, size int64) error {
-		entries, _, err := repo.ListPack(context.TODO(), id)
+		entries, _, err := repo.ListPack(context.TODO(), id, size)
 		if err != nil {
 			t.Fatalf("error listing pack %v: %v", id, err)
 		}

internal/repository/repository.go

@@ -549,20 +549,15 @@ func (r *Repository) List(ctx context.Context, t restic.FileType, fn func(restic
 
 // ListPack returns the list of blobs saved in the pack id and the length of
 // the file as stored in the backend.
-func (r *Repository) ListPack(ctx context.Context, id restic.ID) ([]restic.Blob, int64, error) {
+func (r *Repository) ListPack(ctx context.Context, id restic.ID, size int64) ([]restic.Blob, int64, error) {
 	h := restic.Handle{Type: restic.DataFile, Name: id.String()}
 
-	blobInfo, err := r.Backend().Stat(ctx, h)
+	blobs, err := pack.List(r.Key(), restic.ReaderAt(r.Backend(), h), size)
 	if err != nil {
 		return nil, 0, err
 	}
 
-	blobs, err := pack.List(r.Key(), restic.ReaderAt(r.Backend(), h), blobInfo.Size)
-	if err != nil {
-		return nil, 0, err
-	}
-
-	return blobs, blobInfo.Size, nil
+	return blobs, size, nil
 }
 
 // Delete calls backend.Delete() if implemented, and returns an error

internal/restic/repository.go

@@ -32,7 +32,7 @@ type Repository interface {
 	//
 	// The function fn is called in the same Goroutine List() was called from.
 	List(ctx context.Context, t FileType, fn func(ID, int64) error) error
-	ListPack(context.Context, ID) ([]Blob, int64, error)
+	ListPack(context.Context, ID, int64) ([]Blob, int64, error)
 
 	Flush(context.Context) error