Test and benchmark blob sorting in internal/repository

internal/repository/repository.go

@@ -111,9 +111,13 @@ func (r *Repository) LoadAndDecrypt(ctx context.Context, buf []byte, t restic.Fi
 	return plaintext, nil
 }
 
-// sortCachedPacks moves all cached pack files to the front of blobs.
-func (r *Repository) sortCachedPacks(blobs []restic.PackedBlob) []restic.PackedBlob {
-	if r.Cache == nil {
+type haver interface {
+	Has(restic.Handle) bool
+}
+
+// sortCachedPacksFirst moves all cached pack files to the front of blobs.
+func sortCachedPacksFirst(cache haver, blobs []restic.PackedBlob) []restic.PackedBlob {
+	if cache == nil {
 		return blobs
 	}
 
@@ -126,7 +130,7 @@ func (r *Repository) sortCachedPacks(blobs []restic.PackedBlob) []restic.PackedB
 	noncached := make([]restic.PackedBlob, 0, len(blobs)/2)
 
 	for _, blob := range blobs {
-		if r.Cache.Has(restic.Handle{Type: restic.DataFile, Name: blob.PackID.String()}) {
+		if cache.Has(restic.Handle{Type: restic.DataFile, Name: blob.PackID.String()}) {
 			cached = append(cached, blob)
 			continue
 		}
@@ -149,7 +153,7 @@ func (r *Repository) LoadBlob(ctx context.Context, t restic.BlobType, id restic.
 	}
 
 	// try cached pack files first
-	blobs = r.sortCachedPacks(blobs)
+	blobs = sortCachedPacksFirst(r.Cache, blobs)
 
 	var lastError error
 	for _, blob := range blobs {

internal/repository/repository_internal_test.go

@@ -0,0 +1,81 @@
+package repository
+
+import (
+	"math/rand"
+	"testing"
+
+	"github.com/restic/restic/internal/restic"
+	rtest "github.com/restic/restic/internal/test"
+)
+
+type mapcache map[restic.Handle]struct{}
+
+func (c mapcache) Has(h restic.Handle) bool {
+	_, ok := c[h]
+	return ok
+}
+
+func TestSortCachedPacksFirst(t *testing.T) {
+	var (
+		blobs   [100]restic.PackedBlob
+		blobset = make(map[restic.PackedBlob]struct{})
+		cache   = make(mapcache)
+		r       = rand.New(rand.NewSource(1261))
+	)
+
+	for i := 0; i < len(blobs); i++ {
+		var id restic.ID
+		r.Read(id[:])
+		blobs[i] = restic.PackedBlob{PackID: id}
+		blobset[blobs[i]] = struct{}{}
+
+		if i%3 == 0 {
+			h := restic.Handle{Name: id.String(), Type: restic.DataFile}
+			cache[h] = struct{}{}
+		}
+	}
+
+	sorted := sortCachedPacksFirst(cache, blobs[:])
+
+	rtest.Equals(t, len(blobs), len(sorted))
+	for i := 0; i < len(blobs); i++ {
+		h := restic.Handle{Type: restic.DataFile, Name: sorted[i].PackID.String()}
+		if i < len(cache) {
+			rtest.Assert(t, cache.Has(h), "non-cached blob at front of sorted output")
+		} else {
+			rtest.Assert(t, !cache.Has(h), "cached blob at end of sorted output")
+		}
+		_, ok := blobset[sorted[i]]
+		rtest.Assert(t, ok, "sortCachedPacksFirst changed blob id")
+	}
+}
+
+func BenchmarkSortCachedPacksFirst(b *testing.B) {
+	const nblobs = 512 // Corresponds to a file of ca. 2GB.
+
+	var (
+		blobs [nblobs]restic.PackedBlob
+		cache = make(mapcache)
+		r     = rand.New(rand.NewSource(1261))
+	)
+
+	for i := 0; i < nblobs; i++ {
+		var id restic.ID
+		r.Read(id[:])
+		blobs[i] = restic.PackedBlob{PackID: id}
+
+		if i%3 == 0 {
+			h := restic.Handle{Name: id.String(), Type: restic.DataFile}
+			cache[h] = struct{}{}
+		}
+	}
+
+	var cpy [nblobs]restic.PackedBlob
+	b.ReportAllocs()
+	b.ResetTimer()
+
+	for i := 0; i < b.N; i++ {
+		copy(cpy[:], blobs[:])
+		sortCachedPacksFirst(cache, cpy[:])
+	}
+}