repository: optimize MasterIndex.Each

Sending data through a channel at very high frequency is extremely
inefficient. Thus use simple callbacks instead of channels.

> name                old time/op  new time/op  delta
> MasterIndexEach-16   6.68s ±24%   0.96s ± 2%  -85.64%  (p=0.008 n=5+5)

cmd/restic/cmd_find.go

@@ -467,7 +467,7 @@ func (f *Finder) indexPacksToBlobs(ctx context.Context, packIDs map[string]struc
 
 	// remember which packs were found in the index
 	indexPackIDs := make(map[string]struct{})
-	for pb := range f.repo.Index().Each(wctx) {
+	f.repo.Index().Each(wctx, func(pb restic.PackedBlob) {
 		idStr := pb.PackID.String()
 		// keep entry in packIDs as Each() returns individual index entries
 		matchingID := false
@@ -485,7 +485,7 @@ func (f *Finder) indexPacksToBlobs(ctx context.Context, packIDs map[string]struc
 			f.blobIDs[pb.ID.String()] = struct{}{}
 			indexPackIDs[idStr] = struct{}{}
 		}
-	}
+	})
 
 	for id := range indexPackIDs {
 		delete(packIDs, id)

cmd/restic/cmd_list.go

@@ -64,9 +64,9 @@ func runList(cmd *cobra.Command, opts GlobalOptions, args []string) error {
 			if err != nil {
 				return err
 			}
-			for blobs := range idx.Each(opts.ctx) {
+			idx.Each(opts.ctx, func(blobs restic.PackedBlob) {
 				Printf("%v %v\n", blobs.Type, blobs.ID)
-			}
+			})
 			return nil
 		})
 	default:

cmd/restic/cmd_prune.go

@@ -279,12 +279,12 @@ func planPrune(opts PruneOptions, gopts GlobalOptions, repo restic.Repository, i
 	if len(plan.repackPacks) != 0 {
 		// when repacking, we do not want to keep blobs which are
 		// already contained in kept packs, so delete them from keepBlobs
-		for blob := range repo.Index().Each(ctx) {
+		repo.Index().Each(ctx, func(blob restic.PackedBlob) {
 			if plan.removePacks.Has(blob.PackID) || plan.repackPacks.Has(blob.PackID) {
-				continue
+				return
 			}
 			keepBlobs.Delete(blob.BlobHandle)
-		}
+		})
 	} else {
 		// keepBlobs is only needed if packs are repacked
 		keepBlobs = nil
@@ -299,7 +299,7 @@ func packInfoFromIndex(ctx context.Context, idx restic.MasterIndex, usedBlobs re
 	duplicateBlobs := make(map[restic.BlobHandle]uint8)
 
 	// iterate over all blobs in index to find out which blobs are duplicates
-	for blob := range idx.Each(ctx) {
+	idx.Each(ctx, func(blob restic.PackedBlob) {
 		bh := blob.BlobHandle
 		size := uint64(blob.Length)
 		switch {
@@ -325,7 +325,7 @@ func packInfoFromIndex(ctx context.Context, idx restic.MasterIndex, usedBlobs re
 			stats.size.unused += size
 			stats.blobs.unused++
 		}
-	}
+	})
 
 	// Check if all used blobs have been found in index
 	if len(usedBlobs) != 0 {
@@ -346,7 +346,7 @@ func packInfoFromIndex(ctx context.Context, idx restic.MasterIndex, usedBlobs re
 	}
 
 	// iterate over all blobs in index to generate packInfo
-	for blob := range idx.Each(ctx) {
+	idx.Each(ctx, func(blob restic.PackedBlob) {
 		ip := indexPack[blob.PackID]
 
 		// Set blob type if not yet set
@@ -376,7 +376,7 @@ func packInfoFromIndex(ctx context.Context, idx restic.MasterIndex, usedBlobs re
 		}
 		// update indexPack
 		indexPack[blob.PackID] = ip
-	}
+	})
 
 	// if duplicate blobs exist, those will be set to either "used" or "unused":
 	// - mark only one occurence of duplicate blobs as used
@@ -384,11 +384,11 @@ func packInfoFromIndex(ctx context.Context, idx restic.MasterIndex, usedBlobs re
 	// - if there are no used blobs in a pack, possibly mark duplicates as "unused"
 	if len(duplicateBlobs) > 0 {
 		// iterate again over all blobs in index (this is pretty cheap, all in-mem)
-		for blob := range idx.Each(ctx) {
+		idx.Each(ctx, func(blob restic.PackedBlob) {
 			bh := blob.BlobHandle
 			count, isDuplicate := duplicateBlobs[bh]
 			if !isDuplicate {
-				continue
+				return
 			}
 
 			ip := indexPack[blob.PackID]
@@ -412,7 +412,7 @@ func packInfoFromIndex(ctx context.Context, idx restic.MasterIndex, usedBlobs re
 			}
 			// update indexPack
 			indexPack[blob.PackID] = ip
-		}
+		})
 	}
 
 	return keepBlobs, indexPack, nil

cmd/restic/cmd_recover.go

@@ -66,11 +66,11 @@ func runRecover(gopts GlobalOptions) error {
 	// tree. If it is not referenced, we have a root tree.
 	trees := make(map[restic.ID]bool)
 
-	for blob := range repo.Index().Each(gopts.ctx) {
+	repo.Index().Each(gopts.ctx, func(blob restic.PackedBlob) {
 		if blob.Type == restic.TreeBlob {
 			trees[blob.Blob.ID] = false
 		}
-	}
+	})
 
 	Verbosef("load %d trees\n", len(trees))
 	bar := newProgressMax(!gopts.Quiet, uint64(len(trees)), "trees loaded")

cmd/restic/integration_test.go

@@ -444,11 +444,11 @@ func removePacksExcept(gopts GlobalOptions, t *testing.T, keep restic.IDSet, rem
 	rtest.OK(t, r.LoadIndex(gopts.ctx))
 
 	treePacks := restic.NewIDSet()
-	for pb := range r.Index().Each(context.TODO()) {
+	r.Index().Each(context.TODO(), func(pb restic.PackedBlob) {
 		if pb.Type == restic.TreeBlob {
 			treePacks.Insert(pb.PackID)
 		}
-	}
+	})
 
 	// remove all packs containing data blobs
 	rtest.OK(t, r.List(gopts.ctx, restic.PackFile, func(id restic.ID, size int64) error {
@@ -506,11 +506,11 @@ func TestBackupTreeLoadError(t *testing.T) {
 	rtest.OK(t, err)
 	rtest.OK(t, r.LoadIndex(env.gopts.ctx))
 	treePacks := restic.NewIDSet()
-	for pb := range r.Index().Each(context.TODO()) {
+	r.Index().Each(context.TODO(), func(pb restic.PackedBlob) {
 		if pb.Type == restic.TreeBlob {
 			treePacks.Insert(pb.PackID)
 		}
-	}
+	})
 
 	testRunBackup(t, filepath.Dir(env.testdata), []string{filepath.Base(env.testdata)}, opts, env.gopts)
 	testRunCheck(t, env.gopts)

internal/checker/checker.go

@@ -124,14 +124,14 @@ func (c *Checker) LoadIndex(ctx context.Context) (hints []error, errs []error) {
 
 		debug.Log("process blobs")
 		cnt := 0
-		for blob := range index.Each(ctx) {
+		index.Each(ctx, func(blob restic.PackedBlob) {
 			cnt++
 
 			if _, ok := packToIndex[blob.PackID]; !ok {
 				packToIndex[blob.PackID] = restic.NewIDSet()
 			}
 			packToIndex[blob.PackID].Insert(id)
-		}
+		})
 
 		debug.Log("%d blobs processed", cnt)
 		return nil
@@ -458,13 +458,13 @@ func (c *Checker) UnusedBlobs(ctx context.Context) (blobs restic.BlobHandles) {
 	ctx, cancel := context.WithCancel(ctx)
 	defer cancel()
 
-	for blob := range c.repo.Index().Each(ctx) {
+	c.repo.Index().Each(ctx, func(blob restic.PackedBlob) {
 		h := restic.BlobHandle{ID: blob.ID, Type: blob.Type}
 		if !c.blobRefs.M.Has(h) {
 			debug.Log("blob %v not referenced", h)
 			blobs = append(blobs, h)
 		}
-	}
+	})
 
 	return blobs
 }

internal/pack/pack.go

@@ -370,7 +370,7 @@ func CalculateHeaderSize(blobs []restic.Blob) int {
 func Size(ctx context.Context, mi restic.MasterIndex, onlyHdr bool) map[restic.ID]int64 {
 	packSize := make(map[restic.ID]int64)
 
-	for blob := range mi.Each(ctx) {
+	mi.Each(ctx, func(blob restic.PackedBlob) {
 		size, ok := packSize[blob.PackID]
 		if !ok {
 			size = headerSize
@@ -379,7 +379,7 @@ func Size(ctx context.Context, mi restic.MasterIndex, onlyHdr bool) map[restic.I
 			size += int64(blob.Length)
 		}
 		packSize[blob.PackID] = size + int64(CalculateEntrySize(blob.Blob))
-	}
+	})
 
 	return packSize
 }

internal/repository/index.go

@@ -217,34 +217,22 @@ func (idx *Index) AddToSupersedes(ids ...restic.ID) error {
 	return nil
 }
 
-// Each returns a channel that yields all blobs known to the index. When the
-// context is cancelled, the background goroutine terminates. This blocks any
+// Each passes all blobs known to the index to the callback fn. This blocks any
 // modification of the index.
-func (idx *Index) Each(ctx context.Context) <-chan restic.PackedBlob {
+func (idx *Index) Each(ctx context.Context, fn func(restic.PackedBlob)) {
 	idx.m.Lock()
-
-	ch := make(chan restic.PackedBlob)
-
-	go func() {
 	defer idx.m.Unlock()
-		defer func() {
-			close(ch)
-		}()
 
 	for typ := range idx.byType {
 		m := &idx.byType[typ]
 		m.foreach(func(e *indexEntry) bool {
-				select {
-				case <-ctx.Done():
+			if ctx.Err() != nil {
 				return false
-				case ch <- idx.toPackedBlob(e, restic.BlobType(typ)):
-					return true
 			}
+			fn(idx.toPackedBlob(e, restic.BlobType(typ)))
+			return true
 		})
 	}
-	}()
-
-	return ch
 }
 
 type EachByPackResult struct {

internal/repository/index_test.go

@@ -355,11 +355,11 @@ func TestIndexUnserialize(t *testing.T) {
 }
 
 func listPack(idx *repository.Index, id restic.ID) (pbs []restic.PackedBlob) {
-	for pb := range idx.Each(context.TODO()) {
+	idx.Each(context.TODO(), func(pb restic.PackedBlob) {
 		if pb.PackID.Equal(id) {
 			pbs = append(pbs, pb)
 		}
-	}
+	})
 	return pbs
 }
 

internal/repository/master_index.go

@@ -234,31 +234,16 @@ func (mi *MasterIndex) finalizeFullIndexes() []*Index {
 	return list
 }
 
-// Each returns a channel that yields all blobs known to the index. When the
-// context is cancelled, the background goroutine terminates. This blocks any
-// modification of the index.
-func (mi *MasterIndex) Each(ctx context.Context) <-chan restic.PackedBlob {
+// Each runs fn on all blobs known to the index. When the context is cancelled,
+// the index iteration return immediately. This blocks any modification of the index.
+func (mi *MasterIndex) Each(ctx context.Context, fn func(restic.PackedBlob)) {
 	mi.idxMutex.RLock()
-
-	ch := make(chan restic.PackedBlob)
-
-	go func() {
 	defer mi.idxMutex.RUnlock()
-		defer close(ch)
 
 	for _, idx := range mi.idx {
-			for pb := range idx.Each(ctx) {
-				select {
-				case <-ctx.Done():
-					return
-				case ch <- pb:
+		idx.Each(ctx, fn)
 	}
 }
-		}
-	}()
-
-	return ch
-}
 
 // MergeFinalIndexes merges all final indexes together.
 // After calling, there will be only one big final index in MasterIndex
@@ -450,11 +435,11 @@ func (mi *MasterIndex) ListPacks(ctx context.Context, packs restic.IDSet) <-chan
 			if len(packBlob) == 0 {
 				continue
 			}
-			for pb := range mi.Each(ctx) {
+			mi.Each(ctx, func(pb restic.PackedBlob) {
 				if packs.Has(pb.PackID) && pb.PackID[0]&0xf == i {
 					packBlob[pb.PackID] = append(packBlob[pb.PackID], pb.Blob)
 				}
-			}
+			})
 
 			// pass on packs
 			for packID, pbs := range packBlob {

internal/repository/master_index_test.go

@@ -163,9 +163,9 @@ func TestMasterMergeFinalIndexes(t *testing.T) {
 	rtest.Equals(t, 1, idxCount)
 
 	blobCount := 0
-	for range mIdx.Each(context.TODO()) {
+	mIdx.Each(context.TODO(), func(pb restic.PackedBlob) {
 		blobCount++
-	}
+	})
 	rtest.Equals(t, 2, blobCount)
 
 	blobs := mIdx.Lookup(bhInIdx1)
@@ -195,9 +195,9 @@ func TestMasterMergeFinalIndexes(t *testing.T) {
 	rtest.Equals(t, []restic.PackedBlob{blob2}, blobs)
 
 	blobCount = 0
-	for range mIdx.Each(context.TODO()) {
+	mIdx.Each(context.TODO(), func(pb restic.PackedBlob) {
 		blobCount++
-	}
+	})
 	rtest.Equals(t, 2, blobCount)
 }
 
@@ -316,9 +316,9 @@ func BenchmarkMasterIndexEach(b *testing.B) {
 
 	for i := 0; i < b.N; i++ {
 		entries := 0
-		for _ = range mIdx.Each(context.TODO()) {
+		mIdx.Each(context.TODO(), func(pb restic.PackedBlob) {
 			entries++
-		}
+		})
 	}
 }
 

internal/repository/repository.go

@@ -595,10 +595,15 @@ func (r *Repository) LoadIndex(ctx context.Context) error {
 		// sanity check
 		ctx, cancel := context.WithCancel(ctx)
 		defer cancel()
-		for blob := range r.idx.Each(ctx) {
+
+		invalidIndex := false
+		r.idx.Each(ctx, func(blob restic.PackedBlob) {
 			if blob.IsCompressed() {
-				return errors.Fatal("index uses feature not supported by repository version 1")
+				invalidIndex = true
 			}
+		})
+		if invalidIndex {
+			return errors.Fatal("index uses feature not supported by repository version 1")
 		}
 	}
 

internal/repository/repository_test.go

@@ -362,13 +362,13 @@ func testRepositoryIncrementalIndex(t *testing.T, version uint) {
 		idx, err := loadIndex(context.TODO(), repo, id)
 		rtest.OK(t, err)
 
-		for pb := range idx.Each(context.TODO()) {
+		idx.Each(context.TODO(), func(pb restic.PackedBlob) {
 			if _, ok := packEntries[pb.PackID]; !ok {
 				packEntries[pb.PackID] = make(map[restic.ID]struct{})
 			}
 
 			packEntries[pb.PackID][id] = struct{}{}
-		}
+		})
 		return nil
 	})
 	if err != nil {

internal/restic/repository.go

@@ -83,10 +83,9 @@ type MasterIndex interface {
 	Has(BlobHandle) bool
 	Lookup(BlobHandle) []PackedBlob
 
-	// Each returns a channel that yields all blobs known to the index. When
-	// the context is cancelled, the background goroutine terminates. This
-	// blocks any modification of the index.
-	Each(ctx context.Context) <-chan PackedBlob
+	// Each runs fn on all blobs known to the index. When the context is cancelled,
+	// the index iteration return immediately. This blocks any modification of the index.
+	Each(ctx context.Context, fn func(PackedBlob))
 	ListPacks(ctx context.Context, packs IDSet) <-chan PackBlobs
 
 	Save(ctx context.Context, repo SaverUnpacked, packBlacklist IDSet, extraObsolete IDs, p *progress.Counter) (obsolete IDSet, err error)