index: reduce size of compressed indexes

use the same index size for compressed and uncompressed indexes.
Otherwise, decoding the index of a compressed repository requires
significantly more memory.

internal/repository/repository.go

@@ -588,19 +588,11 @@ func (r *Repository) ListPacksFromIndex(ctx context.Context, packs restic.IDSet)
 // SetIndex instructs the repository to use the given index.
 func (r *Repository) SetIndex(i restic.MasterIndex) error {
 	r.idx = i.(*index.MasterIndex)
-	r.configureIndex()
 	return r.prepareCache()
 }
 
 func (r *Repository) clearIndex() {
 	r.idx = index.NewMasterIndex()
-	r.configureIndex()
-}
-
-func (r *Repository) configureIndex() {
-	if r.cfg.Version >= 2 {
-		r.idx.MarkCompressed()
-	}
 }
 
 // LoadIndex loads all index files from the backend in parallel and stores them

internal/repository/repository_test.go

@@ -376,7 +376,7 @@ func TestRepositoryIncrementalIndex(t *testing.T) {
 func testRepositoryIncrementalIndex(t *testing.T, version uint) {
 	repo, _ := repository.TestRepositoryWithVersion(t, version)
 
-	index.IndexFull = func(*index.Index, bool) bool { return true }
+	index.IndexFull = func(*index.Index) bool { return true }
 
 	// add a few rounds of packs
 	for j := 0; j < 5; j++ {