Free a cached blob once no file still to restore needs it (closes #324)

A restore of selected paths, or one where files failed under
--skip-errors, kept the blobs those files share in the temporary cache
until it ended: the sweeper freed a blob only once every file in the
snapshot database that uses it had been restored, and files outside the
selection or that failed never are.

The sweeper now asks the restore plan instead, which holds only this
run's files and drops each one once it is restored or has failed.

The new test backs up 16 KiB files so it stays quick; the locality
backup helper takes the file size for that.

Model: opus-5-5

README.md

@@ -339,9 +339,7 @@ local index alone, and still exits zero.
 
 **`snapshot purge`**: Remove old snapshots based on criteria. Retention is
 per-snapshot-name (`--keep-latest` keeps the latest of each name, not the
-latest globally). If a snapshot cannot be removed from the local index, the
+latest globally).
-command stops there, leaves that snapshot's metadata on the destination store
-and exits non-zero; `snapshot create --prune` fails the same way.
 * `--keep-latest`: Keep only the most recent snapshot of each name
 * `--older-than <duration>`: Remove snapshots older than duration (e.g. `30d`,
   `4w`, `6mo`, `1y`; `m` is minutes, `mo` is months)

internal/cli/entry_snapshot_purge_test.go

@@ -1,90 +0,0 @@
-package cli //nolint:testpackage // shares runEntry and the hermetic config helpers
-
-import (
-	"context"
-	"database/sql"
-	"os"
-	"path/filepath"
-	"testing"
-	"time"
-
-	"github.com/stretchr/testify/assert"
-	"github.com/stretchr/testify/require"
-	"sneak.berlin/go/vaultik/internal/database"
-	"sneak.berlin/go/vaultik/internal/snapshot"
-	"sneak.berlin/go/vaultik/internal/types"
-)
-
-// The `snapshot purge` command word and flags used below.
-const (
-	cmdPurge       = "purge"
-	flagKeepLatest = "--keep-latest"
-	flagForce      = "--force"
-)
-
-// TestEntrySnapshotPurgeKeepsMetadataWhenLocalIndexDeleteFails makes
-// removing a snapshot from the local index fail and checks that
-// `snapshot purge` exits non-zero and leaves that snapshot's metadata on
-// the destination store. It used to log the error, delete the metadata
-// anyway and exit 0.
-//
-//nolint:paralleltest // replaces os.Args, os.Stdout, os.Stderr and the xdg globals
-func TestEntrySnapshotPurgeKeepsMetadataWhenLocalIndexDeleteFails(t *testing.T) {
-	ctx := context.Background()
-	configPath := writeHermeticPruneConfig(t, false)
-
-	// writeHermeticPruneConfig puts the index and the store directory
-	// beside the config file.
-	dir := filepath.Dir(configPath)
-
-	// Two snapshots of the same name: --keep-latest purges the older.
-	olderStart := time.Date(2026, 5, 1, 9, 0, 0, 0, time.UTC)
-	newerStart := olderStart.Add(time.Hour)
-	olderID := "test-host_test_" + olderStart.Format(time.RFC3339)
-	newerID := "test-host_test_" + newerStart.Format(time.RFC3339)
-
-	db, err := database.New(ctx, filepath.Join(dir, "index.sqlite"))
-	require.NoError(t, err)
-
-	repos := database.NewRepositories(db)
-
-	manifestPaths := make(map[string]string)
-
-	for id, startedAt := range map[string]time.Time{
-		olderID: olderStart,
-		newerID: newerStart,
-	} {
-		completedAt := startedAt.Add(time.Minute)
-		snap := &database.Snapshot{
-			ID:             types.SnapshotID(id),
-			Hostname:       "test-host",
-			VaultikVersion: "test",
-			StartedAt:      startedAt,
-			CompletedAt:    &completedAt,
-		}
-
-		err = repos.WithTx(ctx, func(ctx context.Context, tx *sql.Tx) error {
-			return repos.Snapshots.Create(ctx, tx, snap)
-		})
-		require.NoError(t, err)
-
-		manifestPaths[id] = filepath.Join(dir, "store", "metadata",
-			snapshot.RemoteSnapshotKey(id), "manifest.json.zst")
-		require.NoError(t, os.MkdirAll(filepath.Dir(manifestPaths[id]), 0o750))
-		require.NoError(t, os.WriteFile(manifestPaths[id], []byte("stub"), 0o600))
-	}
-
-	_, err = db.Conn().ExecContext(ctx, `
-		CREATE TRIGGER refuse_snapshot_delete BEFORE DELETE ON snapshots
-		BEGIN SELECT RAISE(ABORT, 'simulated index error'); END`)
-	require.NoError(t, err)
-	require.NoError(t, db.Close())
-
-	code, _, stderr := runEntry(t,
-		flagConfig, configPath, cmdSnapshot, cmdPurge, flagKeepLatest, flagForce)
-
-	assert.Equal(t, 1, code)
-	assert.Contains(t, stderr, "simulated index error")
-	assert.FileExists(t, manifestPaths[olderID],
-		"a snapshot still in the local index keeps its metadata")
-}

internal/storage/file.go

@@ -120,9 +120,10 @@ func (f *FileStorer) Delete(_ context.Context, key string) error {
 	return nil
 }
 
-// List returns all keys with the given prefix. It fails when the
+// List returns all keys with the given prefix, reading through symlinked
-// destination directory is missing; a missing prefix under it is an
+// directories. It fails when the destination directory is missing, or
-// empty listing.
+// when the prefix or a directory above it is a symlink whose target is
+// missing; a prefix that is truly missing is an empty listing.
 func (f *FileStorer) List(ctx context.Context, prefix string) ([]string, error) {
 	var keys []string
 
@@ -133,8 +134,7 @@ func (f *FileStorer) List(ctx context.Context, prefix string) ([]string, error)
 
 	basePath := f.fullPath(prefix)
 
-	// Check if the prefix exists
+	exists, err := f.prefixExists(prefix)
-	exists, err := afero.Exists(f.fs, basePath)
 	if err != nil {
 		return nil, fmt.Errorf("checking path: %w", err)
 	}
@@ -143,7 +143,7 @@ func (f *FileStorer) List(ctx context.Context, prefix string) ([]string, error)
 		return keys, nil // Empty list for non-existent prefix
 	}
 
-	err = afero.Walk(f.fs, basePath, func(path string, info os.FileInfo, err error) error {
+	err = f.walk(basePath, func(path string, info os.FileInfo, err error) error {
 		if err != nil {
 			return err
 		}
@@ -176,7 +176,9 @@ func (f *FileStorer) List(ctx context.Context, prefix string) ([]string, error)
 }
 
 // ListStream returns a channel of ObjectInfo for large result sets. Like
-// List, it sends an error when the destination directory is missing.
+// List, it reads through symlinked directories and sends an error when
+// the destination directory is missing, or when the prefix or a directory
+// above it is a symlink whose target is missing.
 func (f *FileStorer) ListStream(ctx context.Context, prefix string) <-chan ObjectInfo {
 	ch := make(chan ObjectInfo)
 
@@ -192,8 +194,7 @@ func (f *FileStorer) ListStream(ctx context.Context, prefix string) <-chan Objec
 
 		basePath := f.fullPath(prefix)
 
-		// Check if the prefix exists
+		exists, err := f.prefixExists(prefix)
-		exists, err := afero.Exists(f.fs, basePath)
 		if err != nil {
 			ch <- ObjectInfo{Err: fmt.Errorf("checking path: %w", err)}
 
@@ -204,7 +205,7 @@ func (f *FileStorer) ListStream(ctx context.Context, prefix string) <-chan Objec
 			return // Empty channel for non-existent prefix
 		}
 
-		_ = afero.Walk(f.fs, basePath, func(path string, info os.FileInfo, err error) error {
+		_ = f.walk(basePath, func(path string, info os.FileInfo, err error) error {
 			// Check context cancellation
 			select {
 			case <-ctx.Done():
@@ -243,11 +244,12 @@ func (f *FileStorer) ListStream(ctx context.Context, prefix string) <-chan Objec
 }
 
 // DeletePartialUploads removes every file under prefix whose name ends in
-// tempSuffix. A missing prefix has none to remove.
+// tempSuffix. Like List, it reads through symlinked directories and fails
+// on one whose target is missing. A missing prefix has none to remove.
 func (f *FileStorer) DeletePartialUploads(ctx context.Context, prefix string) error {
 	basePath := f.fullPath(prefix)
 
-	exists, err := afero.Exists(f.fs, basePath)
+	exists, err := f.prefixExists(prefix)
 	if err != nil {
 		return fmt.Errorf("checking path: %w", err)
 	}
@@ -256,7 +258,7 @@ func (f *FileStorer) DeletePartialUploads(ctx context.Context, prefix string) er
 		return nil
 	}
 
-	err = afero.Walk(f.fs, basePath, func(path string, info os.FileInfo, err error) error {
+	err = f.walk(basePath, func(path string, info os.FileInfo, err error) error {
 		if err != nil {
 			return err
 		}
@@ -352,6 +354,54 @@ func (f *FileStorer) writeAtomic(
 	return nil
 }
 
+// walk is afero.Walk, except that it reads through a symlinked directory
+// the way Get and Stat do, where afero.Walk reports the link as one file.
+// afero.Walk uses Lstat, which does not follow a link, whenever the
+// filesystem has one; the struct below carries only the afero.Fs methods,
+// so the walk uses Stat instead. A link back up the tree is followed until
+// the operating system refuses the path for too many levels of links, and
+// the walk then fails.
+func (f *FileStorer) walk(root string, fn filepath.WalkFunc) error {
+	return afero.Walk(struct{ afero.Fs }{f.fs}, root, fn)
+}
+
+// prefixExists reports whether prefix exists under the destination
+// directory. It checks each directory on the way down to prefix in turn,
+// and the first one Stat cannot find decides: if it is not there at all,
+// prefix is missing; if it is a symlink whose target is missing, such as
+// a link to a volume that is not mounted, prefixExists fails, since
+// listing it as empty would let prune delete every blob.
+func (f *FileStorer) prefixExists(prefix string) (bool, error) {
+	lstater, canLstat := f.fs.(afero.Lstater)
+	path := f.basePath
+
+	for name := range strings.SplitSeq(prefix, "/") {
+		path = filepath.Join(path, name)
+
+		_, err := f.fs.Stat(path)
+		if err == nil {
+			continue
+		}
+
+		if !os.IsNotExist(err) {
+			return false, err
+		}
+
+		// Lstat does not follow a symlink at path, so it finds the link
+		// that Stat could not follow.
+		if canLstat {
+			_, _, lstatErr := lstater.LstatIfPossible(path)
+			if lstatErr == nil {
+				return false, err
+			}
+		}
+
+		return false, nil
+	}
+
+	return true, nil
+}
+
 // fullPath returns the full filesystem path for a key.
 func (f *FileStorer) fullPath(key string) string {
 	return filepath.Join(f.basePath, key)

internal/storage/file_backend_test.go

@@ -4,7 +4,10 @@ import (
 	"context"
 	"errors"
 	"io/fs"
+	"os"
 	"path/filepath"
+	"reflect"
+	"strings"
 	"testing"
 
 	"sneak.berlin/go/vaultik/internal/storage"
@@ -60,3 +63,232 @@ func TestFileStorerListMissingDestination(t *testing.T) {
 		t.Errorf("ListStream error = %v, want a not-exist error", streamErr)
 	}
 }
+
+// The two directories at the top of a destination, either of which the
+// tests below replace with a symlink.
+const (
+	metadataDir = "metadata"
+	blobsDir    = "blobs"
+)
+
+// moveBehindSymlink moves base/dir to a directory elsewhere and puts a
+// symlink to it in its place.
+func moveBehindSymlink(t *testing.T, base, dir string) {
+	t.Helper()
+
+	linkPath := filepath.Join(base, dir)
+	movedPath := filepath.Join(t.TempDir(), dir)
+
+	err := os.Rename(linkPath, movedPath)
+	if err != nil {
+		t.Fatalf("moving %s away: %v", dir, err)
+	}
+
+	err = os.Symlink(movedPath, linkPath)
+	if err != nil {
+		t.Fatalf("linking %s: %v", dir, err)
+	}
+}
+
+// TestFileStorerListsThroughSymlinkedDirectory checks that List and
+// ListStream read through a symlinked metadata/ or blobs/ directory, as Get
+// and Stat do, instead of listing the link as one key. Listing the whole
+// destination meets the link part-way through the walk; listing its prefix
+// starts the walk at the link. A prefix missing behind the link lists as
+// empty.
+func TestFileStorerListsThroughSymlinkedDirectory(t *testing.T) {
+	t.Parallel()
+
+	for _, dir := range []string{metadataDir, blobsDir} {
+		t.Run(dir, func(t *testing.T) {
+			t.Parallel()
+
+			base := t.TempDir()
+			key := dir + "/aa/bb/object"
+
+			s, err := storage.NewFileStorer(base)
+			if err != nil {
+				t.Fatalf("NewFileStorer: %v", err)
+			}
+
+			err = s.Put(context.Background(), key, strings.NewReader("data"))
+			if err != nil {
+				t.Fatalf("Put: %v", err)
+			}
+
+			moveBehindSymlink(t, base, dir)
+
+			want := []string{key}
+
+			for _, prefix := range []string{"", dir + "/"} {
+				got := listSorted(t, s, prefix)
+				if !reflect.DeepEqual(got, want) {
+					t.Errorf("List(%q) = %v, want %v", prefix, got, want)
+				}
+
+				got = listStreamKeys(t, s, prefix)
+				if !reflect.DeepEqual(got, want) {
+					t.Errorf("ListStream(%q) = %v, want %v", prefix, got, want)
+				}
+			}
+
+			absent := dir + "/absent/"
+
+			if got := listSorted(t, s, absent); len(got) != 0 {
+				t.Errorf("List(%q) = %v, want empty", absent, got)
+			}
+
+			if got := listStreamKeys(t, s, absent); len(got) != 0 {
+				t.Errorf("ListStream(%q) = %v, want empty", absent, got)
+			}
+		})
+	}
+}
+
+// TestFileStorerListFailsOnSymlinkWithMissingTarget checks that List and
+// ListStream fail on a symlinked metadata/ or blobs/ directory whose target
+// is missing, such as a link to a volume that is not mounted, as they do on
+// a missing destination directory, instead of listing it as empty. That
+// holds for a prefix below the link too.
+func TestFileStorerListFailsOnSymlinkWithMissingTarget(t *testing.T) {
+	t.Parallel()
+
+	ctx := context.Background()
+
+	for _, dir := range []string{metadataDir, blobsDir} {
+		t.Run(dir, func(t *testing.T) {
+			t.Parallel()
+
+			base := t.TempDir()
+
+			s, err := storage.NewFileStorer(base)
+			if err != nil {
+				t.Fatalf("NewFileStorer: %v", err)
+			}
+
+			unmounted := filepath.Join(t.TempDir(), "unmounted")
+
+			err = os.Symlink(unmounted, filepath.Join(base, dir))
+			if err != nil {
+				t.Fatalf("Symlink: %v", err)
+			}
+
+			for _, prefix := range []string{"", dir + "/", dir + "/aa/"} {
+				keys, err := s.List(ctx, prefix)
+				if !errors.Is(err, fs.ErrNotExist) {
+					t.Errorf("List(%q) = %v, %v; want a not-exist error",
+						prefix, keys, err)
+				}
+
+				var streamErr error
+
+				for object := range s.ListStream(ctx, prefix) {
+					if object.Err != nil {
+						streamErr = object.Err
+					}
+				}
+
+				if !errors.Is(streamErr, fs.ErrNotExist) {
+					t.Errorf("ListStream(%q) error = %v, want a not-exist error",
+						prefix, streamErr)
+				}
+			}
+		})
+	}
+}
+
+// TestFileStorerListFailsOnSymlinkLoop checks that a symlink pointing back
+// at the destination makes List and ListStream fail instead of walking it
+// forever.
+func TestFileStorerListFailsOnSymlinkLoop(t *testing.T) {
+	t.Parallel()
+
+	ctx := context.Background()
+	base := t.TempDir()
+
+	s, err := storage.NewFileStorer(base)
+	if err != nil {
+		t.Fatalf("NewFileStorer: %v", err)
+	}
+
+	err = s.Put(ctx, testBlobKey, strings.NewReader("data"))
+	if err != nil {
+		t.Fatalf("Put: %v", err)
+	}
+
+	err = os.Symlink(base, filepath.Join(base, "blobs", "loop"))
+	if err != nil {
+		t.Fatalf("Symlink: %v", err)
+	}
+
+	keys, err := s.List(ctx, "blobs/")
+	if err == nil {
+		t.Errorf("List = %d keys and no error, want an error", len(keys))
+	}
+
+	var streamErr error
+
+	for object := range s.ListStream(ctx, "blobs/") {
+		if object.Err != nil {
+			streamErr = object.Err
+		}
+	}
+
+	if streamErr == nil {
+		t.Error("ListStream sent no error, want one")
+	}
+}
+
+// TestFileStorerDeletePartialUploadsThroughSymlinkedDirectory checks that
+// DeletePartialUploads, which remote nuke uses, removes a leftover temp
+// file behind a symlinked metadata/ or blobs/ directory and keeps the
+// object at the real key.
+func TestFileStorerDeletePartialUploadsThroughSymlinkedDirectory(t *testing.T) {
+	t.Parallel()
+
+	ctx := context.Background()
+
+	for _, dir := range []string{metadataDir, blobsDir} {
+		t.Run(dir, func(t *testing.T) {
+			t.Parallel()
+
+			base := t.TempDir()
+			key := dir + "/aa/bb/object"
+
+			s, err := storage.NewFileStorer(base)
+			if err != nil {
+				t.Fatalf("NewFileStorer: %v", err)
+			}
+
+			err = s.Put(ctx, key, strings.NewReader("data"))
+			if err != nil {
+				t.Fatalf("Put: %v", err)
+			}
+
+			leftover := filepath.Join(base, key+"-123456.partial")
+
+			err = os.WriteFile(leftover, []byte("half"), 0o600)
+			if err != nil {
+				t.Fatalf("writing leftover temp file: %v", err)
+			}
+
+			moveBehindSymlink(t, base, dir)
+
+			err = s.DeletePartialUploads(ctx, dir+"/")
+			if err != nil {
+				t.Fatalf("DeletePartialUploads: %v", err)
+			}
+
+			// leftover runs through the link.
+			_, err = os.Stat(leftover)
+			if !os.IsNotExist(err) {
+				t.Errorf("leftover temp file was not removed: %v", err)
+			}
+
+			_, err = s.Stat(ctx, key)
+			if err != nil {
+				t.Errorf("Stat of the real key: %v", err)
+			}
+		})
+	}
+}

internal/vaultik/blobcache.go

@@ -39,9 +39,9 @@ type blobDiskCacheEntry struct {
 // internally and will fall back to LRU eviction if curBytes exceeds
 // maxBytes. Restore passes math.MaxInt64 as maxBytes and drives
 // eviction itself via Delete() through restoreSweeper, which deletes
-// each blob the moment every file that references its chunks has been
+// each blob once no file still to be restored in this run needs it.
-// written. LRU never fires under that configuration; it is kept as a
+// LRU never fires under that configuration; it is kept as a safety net
-// safety net for callers that don't manage eviction themselves.
+// for callers that don't manage eviction themselves.
 //
 // Get/ReadAt/peak-Len counters are debugging instrumentation used by
 // tests to assert that the restore code path uses ReadAt rather than

internal/vaultik/restore.go

@@ -299,12 +299,6 @@ func (v *Vaultik) restoreAllFiles(
 		_ = blobCache.Close()
 	}()
 
-	// Per-restore sweep state: every blob_size_limit/100 bytes written,
-	// scan the cache and delete any blob whose remaining file references
-	// are all already restored.
-	sweeper := newRestoreSweeper(v.ctx, repos, blobCache,
-		v.Config.BlobSizeLimit.Int64()/sweepIntervalDivisor)
-
 	blobByHash, blobIDToHash, err := v.buildBlobIndexes(repos)
 	if err != nil {
 		return nil, err
@@ -316,6 +310,12 @@ func (v *Vaultik) restoreAllFiles(
 		return nil, fmt.Errorf("building restore plan: %w", err)
 	}
 
+	// Per-restore sweep state: every blob_size_limit/100 bytes written,
+	// scan the cache and delete any blob that no pending file in the
+	// plan references.
+	sweeper := newRestoreSweeper(plan, blobCache,
+		v.Config.BlobSizeLimit.Int64()/sweepIntervalDivisor)
+
 	// Ranging over files rather than the map reports them in a stable order.
 	for _, file := range files {
 		if planErr, ok := unplanned[file.ID]; ok {
@@ -403,10 +403,8 @@ func (v *Vaultik) runRestoreLoop(
 			continue
 		}
 
-		// Record the file as restored so the sweeper can free blobs
+		// Drop the file from the plan's indexes so future picks ignore
-		// once all referencing files are done, and drop it from the
+		// it and the sweeper can free blobs no pending file needs.
-		// plan's indexes so future picks ignore it.
-		session.sweeper.fileRestored(fileID.String())
 		plan.finishFile(fileID)
 
 		processed++

internal/vaultik/restore_interrupt_test.go

@@ -74,7 +74,8 @@ func TestRestoreCleansTempDirOnInterrupt(t *testing.T) {
 	buildLocalityFixture(t, fs, dataDir)
 
 	cfg, storer, snapshotID := setupLocalityBackup(
-		context.Background(), t, fs, dataDir, storeDir, dbPath)
+		context.Background(), t, fs, dataDir, storeDir, dbPath,
+		localitySourceBytes)
 
 	// Point the "" temp paths (the blob cache directory and the
 	// snapshot-database directory) at a private directory so the test can

internal/vaultik/restore_locality_test.go

@@ -63,6 +63,10 @@ type localityCopy struct {
 	data []byte
 }
 
+// localitySourceBytes is the size of each source file of the locality
+// fixture.
+const localitySourceBytes = 1024 * 1024
+
 // buildLocalityFixture writes the adversarial source layout described
 // in TestRestoreLocalityAndReadAt: 15 sources of 1 MiB each (which the
 // backup packs into 3 blobs of 5 chunks) plus 9 interleaved-name copies
@@ -73,7 +77,6 @@ func buildLocalityFixture(
 	t.Helper()
 
 	const (
-		srcBytes   = 1024 * 1024
 		srcCount   = 15
 		blobsCount = 3
 		perBlob    = srcCount / blobsCount
@@ -83,7 +86,7 @@ func buildLocalityFixture(
 	for i := range srcCount {
 		s := &localitySource{
 			path: fmt.Sprintf("src-%03d.bin", i+1),
-			data: randomBytes(t, srcBytes),
+			data: randomBytes(t, localitySourceBytes),
 		}
 		sources[i] = s
 		require.NoError(t, afero.WriteFile(
@@ -115,19 +118,20 @@ func buildLocalityFixture(
 
 // setupLocalityBackup runs the backup half of the locality test: a
 // snapshot of dataDir into a file storer with sizes tuned so 15 one-chunk
-// files pack into 3 blobs. The index database is closed before returning
+// files of srcBytes pack into 3 blobs. The index database is closed
-// so the restore half runs from remote bytes only.
+// before returning so the restore half runs from remote bytes only.
 func setupLocalityBackup(
 	ctx context.Context, t *testing.T, fs afero.Fs,
-	dataDir, storeDir, dbPath string,
+	dataDir, storeDir, dbPath string, srcBytes int64,
 ) (*config.Config, *storage.FileStorer, string) {
 	t.Helper()
 
-	// chunkSize avg = 4 MiB makes minSize = 1 MiB, so a 1 MiB file
+	// An average chunk size of four times srcBytes makes the minimum
-	// becomes one chunk. maxBlobSize = 5 MiB packs exactly 5 chunks
+	// chunk srcBytes, so each source file becomes one chunk. A blob limit
-	// per blob, yielding 3 blobs from 15 source files.
+	// of five times srcBytes packs exactly 5 chunks per blob, yielding 3
-	chunkSize := int64(4 * 1024 * 1024)
+	// blobs from 15 source files.
-	maxBlobSize := int64(5 * 1024 * 1024)
+	chunkSize := 4 * srcBytes
+	maxBlobSize := 5 * srcBytes
 
 	storer, err := storage.NewFileStorer(storeDir)
 	require.NoError(t, err)
@@ -208,7 +212,7 @@ func TestRestoreLocalityAndReadAt(t *testing.T) {
 	ctx := context.Background()
 
 	cfg, storer, snapshotID := setupLocalityBackup(
-		ctx, t, fs, dataDir, storeDir, dbPath)
+		ctx, t, fs, dataDir, storeDir, dbPath, localitySourceBytes)
 
 	// Wrap the storer so we can count downloads per blob key.
 	counter := newCountingStorer(storer)

internal/vaultik/restore_plan.go

@@ -31,7 +31,8 @@ var (
 //     with no further downloads.
 //   - blobFiles: for each blob, the set of pending files referencing
 //     it. Used to short-circuit "when this blob lands, which files
-//     become ready" without a global scan.
+//     become ready" without a global scan, and by the sweeper to tell
+//     whether a cached blob is still needed.
 type restorePlan struct {
 	fileBlobs map[types.FileID]map[string]struct{}
 	blobFiles map[string]map[types.FileID]struct{}
@@ -237,6 +238,11 @@ func (p *restorePlan) filesReferencingBlob(blobHash string) []types.FileID {
 	return out
 }
 
+// blobNeeded reports whether any pending file references the named blob.
+func (p *restorePlan) blobNeeded(blobHash string) bool {
+	return len(p.blobFiles[blobHash]) > 0
+}
+
 // hasPending reports whether any unfinished files remain.
 func (p *restorePlan) hasPending() bool {
 	return len(p.fileBlobs) > 0

internal/vaultik/restore_plan_test.go

@@ -63,15 +63,6 @@ func TestRunRestoreLoopFailsOnAbandonedFiles(t *testing.T) {
 
 	t.Cleanup(func() { _ = cache.Close() })
 
-	v := &Vaultik{ctx: ctx}
-	session := &restoreSession{
-		v:       v,
-		ctx:     ctx,
-		repos:   repos,
-		sweeper: newRestoreSweeper(ctx, repos, cache, 1),
-		result:  &RestoreResult{},
-	}
-
 	// A file that is still pending but whose uncached-blob set is empty
 	// and which was never queued as ready: the loop can neither restore
 	// nor download it. This is the abandonment the guard must catch.
@@ -83,6 +74,15 @@ func TestRunRestoreLoopFailsOnAbandonedFiles(t *testing.T) {
 		cached:    map[string]struct{}{},
 	}
 
+	v := &Vaultik{ctx: ctx}
+	session := &restoreSession{
+		v:       v,
+		ctx:     ctx,
+		repos:   repos,
+		sweeper: newRestoreSweeper(plan, cache, 1),
+		result:  &RestoreResult{},
+	}
+
 	err = v.runRestoreLoop(session, plan, map[types.FileID]*database.File{}, 0)
 	require.ErrorIs(t, err, errRestoreIncomplete)
 }

internal/vaultik/restore_sweeper.go

@@ -1,46 +1,30 @@
 package vaultik
 
-import (
+// restoreSweeper frees cached blobs once no file still to be restored in
-	"context"
+// this run needs them. It works as follows:
-	"fmt"
-
-	"sneak.berlin/go/vaultik/internal/database"
-	"sneak.berlin/go/vaultik/internal/log"
-)
-
-// restoreSweeper frees cached blobs once all files that reference any of
-// their chunks have been restored. It works as follows:
 //
-//  1. Callers add a file's ID to an in-memory restored set via
+//  1. After each chunk is restored, chunkRestored accumulates a running
-//     fileRestored once the file is fully written to disk.
-//  2. After each chunk is restored, chunkRestored accumulates a running
 //     byte count.
-//  3. When the accumulator crosses a threshold (one hundredth of the
+//  2. When the accumulator crosses a threshold (one hundredth of the
 //     configured blob size — so a sweep runs about a hundred times per
 //     blob's worth of restored bytes), the sweeper iterates every key in
-//     the cache. For each cached blob it asks the DB which files
+//     the cache and deletes each blob that the restore plan no longer
-//     reference any chunk in that blob, then compares that list against
+//     needs.
-//     the in-memory restored set. If any referencing file is missing
-//     from the set the blob is kept; otherwise the cache entry is
-//     deleted.
 //
-// All DB reads happen against the snapshot's temporary metadata DB,
+// The plan drops a file once it is restored or has failed, and holds
-// which is local, indexed, and not under contention — the queries are
+// only the files this run restores, so files outside the requested paths
-// cheap and run at most once per blob per sweep interval.
+// never keep a blob.
 type restoreSweeper struct {
-	ctx        context.Context //nolint:containedctx // ctx bound at construction by design
+	plan       *restorePlan
-	repos      *database.Repositories
 	cache      *blobDiskCache
 	threshold  int64
 	bytesAccum int64
-	restored   map[string]struct{}
 }
 
 // newRestoreSweeper returns a sweeper that triggers eviction every
 // `threshold` bytes restored. Callers should pass blob_size_limit/100.
 func newRestoreSweeper(
-	ctx context.Context,
+	plan *restorePlan,
-	repos *database.Repositories,
 	cache *blobDiskCache,
 	threshold int64,
 ) *restoreSweeper {
@@ -49,21 +33,12 @@ func newRestoreSweeper(
 	}
 
 	return &restoreSweeper{
-		ctx:       ctx,
+		plan:      plan,
-		repos:     repos,
 		cache:     cache,
 		threshold: threshold,
-		restored:  make(map[string]struct{}),
 	}
 }
 
-// fileRestored records a file as fully restored. After this call, any
-// blob whose only remaining references come from files in the restored
-// set may be evicted on the next sweep.
-func (s *restoreSweeper) fileRestored(fileID string) {
-	s.restored[fileID] = struct{}{}
-}
-
 // chunkRestored accounts n bytes against the sweep threshold and runs a
 // sweep if the threshold has been crossed since the last sweep.
 func (s *restoreSweeper) chunkRestored(n int64) {
@@ -76,60 +51,11 @@ func (s *restoreSweeper) chunkRestored(n int64) {
 	s.sweep()
 }
 
-// sweep deletes any cached blob whose chunks are no longer referenced
+// sweep deletes every cached blob that no pending file references.
-// by an unrestored file. Per-blob DB failures are logged and the blob
-// is kept — we'd rather hold a blob longer than risk a re-download.
 func (s *restoreSweeper) sweep() {
 	for _, blobHash := range s.cache.Keys() {
-		needed, err := s.blobStillNeeded(blobHash)
+		if !s.plan.blobNeeded(blobHash) {
-		if err != nil {
-			log.Debug("sweeper referencing-files query failed",
-				"blob_hash", blobHash[:16], "error", err)
-
-			continue
-		}
-
-		if !needed {
 			s.cache.Delete(blobHash)
 		}
 	}
 }
-
-// blobStillNeeded returns true if any file that references a chunk in
-// this blob has not yet been restored. On any error the function
-// returns true — keeping the blob is always the safe answer because we
-// can't prove we're done with it.
-func (s *restoreSweeper) blobStillNeeded(blobHash string) (bool, error) {
-	rows, err := s.repos.DB().Conn().QueryContext(s.ctx, `
-		SELECT DISTINCT fc.file_id
-		FROM file_chunks fc
-		JOIN blob_chunks bc ON bc.chunk_hash = fc.chunk_hash
-		JOIN blobs b ON b.id = bc.blob_id
-		WHERE b.blob_hash = ?
-	`, blobHash)
-	if err != nil {
-		return true, fmt.Errorf("querying referencing files: %w", err)
-	}
-
-	defer func() { _ = rows.Close() }()
-
-	for rows.Next() {
-		var fileID string
-
-		err := rows.Scan(&fileID)
-		if err != nil {
-			return true, fmt.Errorf("scanning file_id: %w", err)
-		}
-
-		if _, ok := s.restored[fileID]; !ok {
-			return true, nil
-		}
-	}
-
-	err = rows.Err()
-	if err != nil {
-		return true, err
-	}
-
-	return false, nil
-}

internal/vaultik/restore_sweeper_test.go

@@ -0,0 +1,163 @@
+package vaultik //nolint:testpackage // reads the restore blob cache's peak size
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"path/filepath"
+	"testing"
+
+	"github.com/spf13/afero"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"sneak.berlin/go/vaultik/internal/config"
+	"sneak.berlin/go/vaultik/internal/log"
+	"sneak.berlin/go/vaultik/internal/storage"
+	"sneak.berlin/go/vaultik/internal/ui"
+)
+
+// TestRestoreFreesBlobsNoPendingFileNeeds asserts that the restore cache
+// frees a blob once no file still to be restored in this run needs it.
+// Every original file has a copy with the same content, so every blob
+// holds chunks of copies: a restore that leaves the copies out of its
+// paths, or fails on them, must not keep the blobs for them.
+func TestRestoreFreesBlobsNoPendingFileNeeds(t *testing.T) {
+	log.Initialize(log.Config{})
+	t.Parallel()
+
+	// Small files keep the backup and both restores quick.
+	const fileBytes = 16 * 1024
+
+	fs := afero.NewOsFs()
+	tempDir := t.TempDir()
+
+	dataDir := filepath.Join(tempDir, "source")
+	originalsDir := filepath.Join(dataDir, "originals")
+	copiesDir := filepath.Join(dataDir, "copies")
+	storeDir := filepath.Join(tempDir, "remote")
+	dbPath := filepath.Join(tempDir, "index.sqlite")
+
+	originals := writeFilesWithCopies(t, fs, originalsDir, copiesDir, fileBytes)
+
+	ctx := context.Background()
+
+	cfg, storer, snapshotID := setupLocalityBackup(
+		ctx, t, fs, dataDir, storeDir, dbPath, fileBytes)
+
+	t.Run("restore by path", func(t *testing.T) {
+		t.Parallel()
+
+		restoreDir := filepath.Join(tempDir, "by-path")
+
+		peak, err := restorePeakCachedBlobs(ctx, t, fs, cfg, storer,
+			&RestoreOptions{
+				SnapshotID: snapshotID,
+				TargetDir:  restoreDir,
+				Paths:      []string{originalsDir},
+			})
+		require.NoError(t, err)
+
+		requireRestoredFiles(t, fs, restoreDir, originals)
+		assert.LessOrEqualf(t, peak, 1,
+			"peak cached blobs was %d; blobs were kept for unselected files",
+			peak)
+	})
+
+	t.Run("restore with failed files", func(t *testing.T) {
+		t.Parallel()
+
+		restoreDir := filepath.Join(tempDir, "with-failures")
+
+		// A regular file where the copies directory belongs makes every
+		// copy fail to restore.
+		blocker := filepath.Join(restoreDir, copiesDir)
+		require.NoError(t, fs.MkdirAll(filepath.Dir(blocker), 0o755))
+		require.NoError(t, afero.WriteFile(fs, blocker, nil, 0o644))
+
+		peak, err := restorePeakCachedBlobs(ctx, t, fs, cfg, storer,
+			&RestoreOptions{
+				SnapshotID: snapshotID,
+				TargetDir:  restoreDir,
+				SkipErrors: true,
+			})
+		require.ErrorIs(t, err, errFilesFailedRestore)
+
+		requireRestoredFiles(t, fs, restoreDir, originals)
+		assert.LessOrEqualf(t, peak, 1,
+			"peak cached blobs was %d; blobs were kept for failed files", peak)
+	})
+}
+
+// writeFilesWithCopies writes 15 random files of fileBytes into
+// originalsDir and a copy of each into copiesDir. With
+// setupLocalityBackup given the same size, each file is one chunk and the
+// 15 chunks fill 3 blobs. Returns the originals' content by path.
+func writeFilesWithCopies(
+	t *testing.T, fs afero.Fs, originalsDir, copiesDir string, fileBytes int,
+) map[string][]byte {
+	t.Helper()
+
+	const fileCount = 15
+
+	require.NoError(t, fs.MkdirAll(originalsDir, 0o755))
+	require.NoError(t, fs.MkdirAll(copiesDir, 0o755))
+
+	originals := make(map[string][]byte, fileCount)
+
+	for i := range fileCount {
+		name := fmt.Sprintf("file-%02d.bin", i)
+		data := randomBytes(t, fileBytes)
+		original := filepath.Join(originalsDir, name)
+		originals[original] = data
+
+		require.NoError(t, afero.WriteFile(fs, original, data, 0o644))
+		require.NoError(t, afero.WriteFile(
+			fs, filepath.Join(copiesDir, name), data, 0o644))
+	}
+
+	return originals
+}
+
+// requireRestoredFiles requires every file in want to have been restored
+// under restoreDir with its content intact.
+func requireRestoredFiles(
+	t *testing.T, fs afero.Fs, restoreDir string, want map[string][]byte,
+) {
+	t.Helper()
+
+	for path, data := range want {
+		got, err := afero.ReadFile(fs, filepath.Join(restoreDir, path))
+		require.NoErrorf(t, err, "file missing after restore: %s", path)
+		require.Equalf(t, data, got, "byte mismatch for %s", path)
+	}
+}
+
+// restorePeakCachedBlobs runs a restore and returns the most blobs its
+// cache held at once, together with the restore's error.
+func restorePeakCachedBlobs(
+	ctx context.Context, t *testing.T, fs afero.Fs,
+	cfg *config.Config, storer storage.Storer, opts *RestoreOptions,
+) (int, error) {
+	t.Helper()
+
+	var cache *blobDiskCache
+
+	v := &Vaultik{
+		Config:  cfg,
+		Storage: storer,
+		Fs:      fs,
+		Stdout:  io.Discard,
+		Stderr:  io.Discard,
+		UI:      ui.NewWithColor(io.Discard, false),
+		restoreCacheObserver: func(c *blobDiskCache) {
+			cache = c
+		},
+	}
+	v.SetContext(ctx)
+
+	err := v.Restore(opts)
+
+	require.NotNil(t, cache, "restoreCacheObserver must fire during restore")
+
+	return cache.PeakLen(), err
+}

internal/vaultik/snapshot.go

@@ -627,8 +627,7 @@ func selectSnapshotsToPurge(
 }
 
 // confirmAndExecutePurge shows deletion candidates, confirms with the
-// user, and deletes snapshots. It stops with an error at the first
+// user, and deletes snapshots.
-// snapshot it cannot delete.
 func (v *Vaultik) confirmAndExecutePurge(
 	toDelete []SnapshotInfo, force, quiet bool,
 ) error {
@@ -670,11 +669,10 @@ func (v *Vaultik) confirmAndExecutePurge(
 		snapshotID := snap.ID.String()
 		log.Info("Deleting snapshot", "id", snapshotID)
 
-		// Stop before the remote delete: a snapshot still in the local
-		// index must keep its metadata on the destination store.
 		err := v.deleteSnapshotFromLocalDB(snapshotID)
 		if err != nil {
-			return fmt.Errorf("deleting snapshot %s from local index: %w", snapshotID, err)
+			log.Error("Failed to delete from local database",
+				"snapshot_id", snapshotID, "error", err)
 		}
 
 		_, err = v.deleteRemoteSnapshotByKey(snapshot.RemoteSnapshotKey(snapshotID))

internal/vaultik/symlinked_destination_test.go

@@ -0,0 +1,147 @@
+package vaultik_test
+
+import (
+	"context"
+	"io/fs"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"sneak.berlin/go/vaultik/internal/log"
+	"sneak.berlin/go/vaultik/internal/vaultik"
+)
+
+// TestPruneDeletesNothingThroughSymlinkedDirectory checks that prune keeps
+// every blob and the local snapshot record when the metadata/ or blobs/
+// directory of a file:// destination is a symlink to a directory elsewhere
+// (https://git.eeqj.de/sneak/vaultik/issues/296). A backup writes through
+// such a link, so prune has to list through it too.
+func TestPruneDeletesNothingThroughSymlinkedDirectory(t *testing.T) {
+	log.Initialize(log.Config{})
+	t.Parallel()
+
+	for _, dir := range []string{"metadata", "blobs"} {
+		t.Run(dir, func(t *testing.T) {
+			t.Parallel()
+
+			ctx := context.Background()
+			storeDir := filepath.Join(t.TempDir(), "store")
+			v, repos, _ := backUpToFileDestination(ctx, t, storeDir)
+			blobFiles := blobFilesIn(t, storeDir)
+			moveBehindSymlink(t, storeDir, dir)
+
+			require.NoError(t, v.Prune(&vaultik.PruneOptions{Force: true}))
+
+			// When blobs/ is the link, these paths run through it.
+			for _, blobFile := range blobFiles {
+				assert.FileExists(t, blobFile, "prune must delete no blob")
+			}
+
+			snapshots, err := repos.Snapshots.ListRecent(ctx, listRecentTestLimit)
+			require.NoError(t, err)
+			assert.Len(t, snapshots, 1, "prune must delete no local snapshot record")
+		})
+	}
+}
+
+// TestPruneFailsOnSymlinkedDirectoryWithMissingTarget checks that prune
+// fails, deleting no blob and keeping the local snapshot record, when the
+// metadata/ or blobs/ directory of a file:// destination is a symlink
+// whose target is missing, as a link to a volume that is not mounted is.
+func TestPruneFailsOnSymlinkedDirectoryWithMissingTarget(t *testing.T) {
+	log.Initialize(log.Config{})
+	t.Parallel()
+
+	for _, dir := range []string{"metadata", "blobs"} {
+		t.Run(dir, func(t *testing.T) {
+			t.Parallel()
+
+			ctx := context.Background()
+			storeDir := filepath.Join(t.TempDir(), "store")
+			v, repos, _ := backUpToFileDestination(ctx, t, storeDir)
+			blobFiles := blobFilesIn(t, storeDir)
+			targetPath := moveBehindSymlink(t, storeDir, dir)
+
+			// Unmount the volume the link points to, and mount it again
+			// once prune has run.
+			unmountedPath := targetPath + "-unmounted"
+			require.NoError(t, os.Rename(targetPath, unmountedPath))
+
+			err := v.Prune(&vaultik.PruneOptions{Force: true})
+			require.ErrorIs(t, err, fs.ErrNotExist)
+
+			require.NoError(t, os.Rename(unmountedPath, targetPath))
+
+			// When blobs/ is the link, these paths run through it.
+			for _, blobFile := range blobFiles {
+				assert.FileExists(t, blobFile, "prune must delete no blob")
+			}
+
+			snapshots, err := repos.Snapshots.ListRecent(ctx, listRecentTestLimit)
+			require.NoError(t, err)
+			assert.Len(t, snapshots, 1, "prune must delete no local snapshot record")
+		})
+	}
+}
+
+// TestRemoveSnapshotWarnsOnSymlinkedMetadataWithMissingTarget checks that
+// snapshot remove warns that the metadata could not be removed from the
+// destination when metadata/ is a symlink whose target is missing, as it
+// does when the destination directory is missing, instead of finding no
+// metadata to remove.
+func TestRemoveSnapshotWarnsOnSymlinkedMetadataWithMissingTarget(t *testing.T) {
+	log.Initialize(log.Config{})
+	t.Parallel()
+
+	ctx := context.Background()
+	storeDir := filepath.Join(t.TempDir(), "store")
+	v, repos, out := backUpToFileDestination(ctx, t, storeDir)
+	targetPath := moveBehindSymlink(t, storeDir, "metadata")
+	require.NoError(t, os.Rename(targetPath, targetPath+"-unmounted"))
+
+	result, err := v.RemoveSnapshot(localSnapshotID(ctx, t, repos, "first"),
+		&vaultik.RemoveOptions{Force: true})
+	require.NoError(t, err)
+
+	assert.False(t, result.RemoteRemoved)
+	assert.Contains(t, out.String(),
+		"Could not remove snapshot metadata from remote")
+	assert.NotContains(t, out.String(),
+		"Removed snapshot metadata from remote storage")
+}
+
+// blobFilesIn returns the paths of the blob files under storeDir/blobs, and
+// fails the test when there are none.
+func blobFilesIn(t *testing.T, storeDir string) []string {
+	t.Helper()
+
+	var blobFiles []string
+
+	err := filepath.WalkDir(filepath.Join(storeDir, "blobs"),
+		func(path string, entry fs.DirEntry, err error) error {
+			if err == nil && !entry.IsDir() {
+				blobFiles = append(blobFiles, path)
+			}
+
+			return err
+		})
+	require.NoError(t, err)
+	require.NotEmpty(t, blobFiles)
+
+	return blobFiles
+}
+
+// moveBehindSymlink moves storeDir/dir to a directory elsewhere, puts a
+// symlink to it in its place, and returns where it went.
+func moveBehindSymlink(t *testing.T, storeDir, dir string) string {
+	t.Helper()
+
+	linkPath := filepath.Join(storeDir, dir)
+	targetPath := filepath.Join(t.TempDir(), dir)
+	require.NoError(t, os.Rename(linkPath, targetPath))
+	require.NoError(t, os.Symlink(targetPath, linkPath))
+
+	return targetPath
+}