Merge final indexes together for faster index access

internal/checker/checker.go

@@ -190,6 +190,8 @@ func (c *Checker) LoadIndex(ctx context.Context) (hints []error, errs []error) {
 		}
 	}
 
+	c.masterIndex.MergeFinalIndexes()
+
 	err = c.repo.SetIndex(c.masterIndex)
 	if err != nil {
 		debug.Log("SetIndex returned error: %v", err)

internal/repository/index.go

@@ -50,7 +50,7 @@ type Index struct {
 	packIDToIndex map[restic.ID]int
 
 	final      bool       // set to true for all indexes read from the backend ("finalized")
-	id         restic.ID // set to the ID of the index when it's finalized
+	ids        restic.IDs // set to the IDs of the contained finalized indexes
 	supersedes restic.IDs
 	created    time.Time
 }
@@ -393,17 +393,17 @@ func (idx *Index) Finalize() {
 	idx.packIDToIndex = nil
 }
 
-// ID returns the ID of the index, if available. If the index is not yet
+// ID returns the IDs of the index, if available. If the index is not yet
 // finalized, an error is returned.
-func (idx *Index) ID() (restic.ID, error) {
+func (idx *Index) IDs() (restic.IDs, error) {
 	idx.m.Lock()
 	defer idx.m.Unlock()
 
 	if !idx.final {
-		return restic.ID{}, errors.New("index not finalized")
+		return nil, errors.New("index not finalized")
 	}
 
-	return idx.id, nil
+	return idx.ids, nil
 }
 
 // SetID sets the ID the index has been written to. This requires that
@@ -416,12 +416,12 @@ func (idx *Index) SetID(id restic.ID) error {
 		return errors.New("index is not final")
 	}
 
-	if !idx.id.IsNull() {
+	if len(idx.ids) > 0 {
 		return errors.New("ID already set")
 	}
 
 	debug.Log("ID set to %v", id)
-	idx.id = id
+	idx.ids = append(idx.ids, id)
 
 	return nil
 }
@@ -462,6 +462,38 @@ func (idx *Index) TreePacks() restic.IDs {
 	return idx.treePacks
 }
 
+// merge() merges indexes, i.e. idx.merge(idx2) merges the contents of idx2 into idx.
+// idx2 is not changed by this method.
+func (idx *Index) merge(idx2 *Index) error {
+	idx.m.Lock()
+	defer idx.m.Unlock()
+	idx2.m.Lock()
+	defer idx2.m.Unlock()
+
+	if !idx2.final {
+		return errors.New("index to merge is not final!")
+	}
+
+	packlen := len(idx.packs)
+	// copy all index entries of idx2 to idx
+	for typ := range idx2.byType {
+		m2 := &idx2.byType[typ]
+		m := &idx.byType[typ]
+		m2.foreach(func(entry *indexEntry) bool {
+			// packIndex is changed as idx2.pack is appended to idx.pack, see below
+			m.add(entry.id, entry.packIndex+packlen, entry.offset, entry.length)
+			return true
+		})
+	}
+
+	idx.packs = append(idx.packs, idx2.packs...)
+	idx.treePacks = append(idx.treePacks, idx2.treePacks...)
+	idx.ids = append(idx.ids, idx2.ids...)
+	idx.supersedes = append(idx.supersedes, idx2.supersedes...)
+
+	return nil
+}
+
 // isErrOldIndex returns true if the error may be caused by an old index
 // format.
 func isErrOldIndex(err error) bool {
@@ -581,7 +613,7 @@ func LoadIndexWithDecoder(ctx context.Context, repo restic.Repository, buf []byt
 		return nil, buf[:0], err
 	}
 
-	idx.id = id
+	idx.ids = append(idx.ids, id)
 
 	return idx, buf, nil
 }

internal/repository/index_test.go

@@ -135,10 +135,9 @@ func TestIndexSerialize(t *testing.T) {
 
 	id := restic.NewRandomID()
 	rtest.OK(t, idx.SetID(id))
-	id2, err := idx.ID()
+	ids, err := idx.IDs()
 	rtest.OK(t, err)
-	rtest.Assert(t, id2.Equal(id),
+	rtest.Equals(t, restic.IDs{id}, ids)
-		"wrong ID returned: want %v, got %v", id, id2)
 
 	idx3, err := repository.DecodeIndex(wr3.Bytes())
 	rtest.OK(t, err)

internal/repository/master_index.go

@@ -18,7 +18,12 @@ type MasterIndex struct {
 
 // NewMasterIndex creates a new master index.
 func NewMasterIndex() *MasterIndex {
-	return &MasterIndex{pendingBlobs: restic.NewBlobSet()}
+	// Always add an empty final index, such that MergeFinalIndexes can merge into this.
+	// Note that removing this index could lead to a race condition in the rare
+	// sitation that only two indexes exist which are saved and merged concurrently.
+	idx := []*Index{NewIndex()}
+	idx[0].Finalize()
+	return &MasterIndex{idx: idx, pendingBlobs: restic.NewBlobSet()}
 }
 
 // Lookup queries all known Indexes for the ID and returns the first match.
@@ -237,6 +242,31 @@ func (mi *MasterIndex) Each(ctx context.Context) <-chan restic.PackedBlob {
 	return ch
 }
 
+// MergeFinalIndexes merges all final indexes together.
+// After calling, there will be only one big final index in MasterIndex
+// containing all final index contents.
+// Indexes that are not final are left untouched.
+// This merging can only be called after all index files are loaded - as
+// removing of superseded index contents is only possible for unmerged indexes.
+func (mi *MasterIndex) MergeFinalIndexes() {
+	mi.idxMutex.Lock()
+	defer mi.idxMutex.Unlock()
+
+	// The first index is always final and the one to merge into
+	newIdx := mi.idx[:1]
+	for i := 1; i < len(mi.idx); i++ {
+		idx := mi.idx[i]
+		// clear reference in masterindex as it may become stale
+		mi.idx[i] = nil
+		if !idx.Final() {
+			newIdx = append(newIdx, idx)
+		} else {
+			mi.idx[0].merge(idx)
+		}
+	}
+	mi.idx = newIdx
+}
+
 // RebuildIndex combines all known indexes to a new index, leaving out any
 // packs whose ID is contained in packBlacklist. The new index contains the IDs
 // of all known indexes in the "supersedes" field.
@@ -267,15 +297,15 @@ func (mi *MasterIndex) RebuildIndex(packBlacklist restic.IDSet) (*Index, error)
 			continue
 		}
 
-		id, err := idx.ID()
+		ids, err := idx.IDs()
 		if err != nil {
 			debug.Log("index %d does not have an ID: %v", err)
 			return nil, err
 		}
 
-		debug.Log("adding index id %v to supersedes field", id)
+		debug.Log("adding index ids %v to supersedes field", ids)
 
-		err = newIndex.AddToSupersedes(id)
+		err = newIndex.AddToSupersedes(ids...)
 		if err != nil {
 			return nil, err
 		}

internal/repository/repository.go

@@ -361,13 +361,15 @@ func (r *Repository) SetIndex(i restic.Index) error {
 
 	ids := restic.NewIDSet()
 	for _, idx := range r.idx.All() {
-		id, err := idx.ID()
+		indexIDs, err := idx.IDs()
 		if err != nil {
 			debug.Log("not using index, ID() returned error %v", err)
 			continue
 		}
+		for _, id := range indexIDs {
 			ids.Insert(id)
 		}
+	}
 
 	return r.PrepareCache(ids)
 }
@@ -396,6 +398,7 @@ func (r *Repository) saveIndex(ctx context.Context, indexes ...*Index) error {
 
 		debug.Log("Saved index %d as %v", i, sid)
 	}
+	r.idx.MergeFinalIndexes()
 
 	return nil
 }
@@ -479,12 +482,16 @@ func (r *Repository) LoadIndex(ctx context.Context) error {
 	validIndex := restic.NewIDSet()
 	wg.Go(func() error {
 		for idx := range indexCh {
-			id, err := idx.ID()
+			ids, err := idx.IDs()
 			if err == nil {
+				for _, id := range ids {
 					validIndex.Insert(id)
 				}
+			}
+
 			r.idx.Insert(idx)
 		}
+		r.idx.MergeFinalIndexes()
 		return nil
 	})