go/storage: Add automatic storage backend detection

.changelog/5876.cfg.md

@@ -0,0 +1,12 @@
+The pathbadger storage backend is now the default for new nodes
+
+When a node is provisioned into an empty data directory it will default to
+using the `pathbadger` storage backend.
+
+For existing nodes, the storage backend is automatically detected based on
+the data directory. When multiple storage directories exist, the one most
+recently modified is used.
+
+In case one does not want this new behavior, it is still possible to set
+the `storage.backend` to `badger`/`pathbadger` to explicitly configure the
+desired storage backend and disable autodetection.

.changelog/5876.feature.md

@@ -0,0 +1,8 @@
+go/storage: Add automatic storage backend detection
+
+The new default storage backend is "auto" which attempts to detect the
+storage backend that should be used based on existing data directories.
+When none exist, "pathbadger" is used. When multiple exist, the most
+recently modified one is used.
+
+This should make newly deployed nodes default to pathbadger.

go/oasis-test-runner/oasis/oasis.go

@@ -41,7 +41,7 @@ const (
 	defaultVRFInterval        = 20
 	defaultVRFSubmissionDelay = 5
 
-	defaultStorageBackend = database.BackendNamePathBadger
+	defaultStorageBackend = database.BackendNameAuto
 
 	logNodeFile        = "node.log"
 	logConsoleFile     = "console.log"

go/storage/database/database.go

@@ -5,7 +5,10 @@ import (
 	"context"
 	"fmt"
 	"io"
+	"os"
 	"path/filepath"
+	"slices"
+	"time"
 
 	"github.com/oasisprotocol/oasis-core/go/storage/api"
 	"github.com/oasisprotocol/oasis-core/go/storage/mkvs/checkpoint"
@@ -14,11 +17,17 @@ import (
 )
 
 const (
+	// BackendNameAuto is the name of the automatic backend detection "backend".
+	BackendNameAuto = "auto"
 	// BackendNameBadgerDB is the name of the BadgerDB backed database backend.
 	BackendNameBadgerDB = "badger"
 	// BackendNamePathBadger is the name of the PathBadger database backend.
 	BackendNamePathBadger = "pathbadger"
 
+	// autoDefaultBackend is the default backend in case automatic backend detection is enabled and
+	// no previous backend exists.
+	autoDefaultBackend = BackendNamePathBadger
+
 	checkpointDir = "checkpoints"
 )
 
@@ -39,6 +48,10 @@ type databaseBackend struct {
 
 // New constructs a new database backed storage Backend instance.
 func New(cfg *api.Config) (api.LocalBackend, error) {
+	if err := autoDetectBackend(cfg); err != nil {
+		return nil, err
+	}
+
 	ndb, err := db.New(cfg.Backend, cfg.ToNodeDB())
 	if err != nil {
 		return nil, fmt.Errorf("storage/database: failed to create node database: %w", err)
@@ -164,3 +177,59 @@ func (ba *databaseBackend) Checkpointer() checkpoint.CreateRestorer {
 func (ba *databaseBackend) NodeDB() dbApi.NodeDB {
 	return ba.ndb
 }
+
+// autoDetectBackend attempts automatic backend detection, modifying the configuration in place.
+func autoDetectBackend(cfg *api.Config) error {
+	if cfg.Backend != BackendNameAuto {
+		return nil
+	}
+
+	// Make sure that the DefaultFileName was used to derive the subdirectory. Otherwise automatic
+	// detection cannot be performed.
+	if filepath.Base(cfg.DB) != DefaultFileName(cfg.Backend) {
+		return fmt.Errorf("storage/database: 'auto' backend selected using a non-default path")
+	}
+
+	// Perform automatic database backend detection if selected. Detection will be based on existing
+	// database directories. If multiple directories are available, the most recently modified is
+	// selected.
+	type foundBackend struct {
+		path      string
+		timestamp time.Time
+		name      string
+	}
+	var backends []foundBackend
+
+	for _, b := range db.Backends {
+		// Generate expected filename for the given backend.
+		fn := DefaultFileName(b.Name())
+		maybeDb := filepath.Join(filepath.Dir(cfg.DB), fn)
+		fi, err := os.Stat(maybeDb)
+		if err != nil {
+			continue
+		}
+
+		backends = append(backends, foundBackend{
+			path:      maybeDb,
+			timestamp: fi.ModTime(),
+			name:      b.Name(),
+		})
+	}
+	slices.SortFunc(backends, func(a, b foundBackend) int {
+		return a.timestamp.Compare(b.timestamp)
+	})
+
+	// If no existing backends are available, default to "pathbadger".
+	if len(backends) == 0 {
+		cfg.Backend = autoDefaultBackend
+		cfg.DB = filepath.Join(filepath.Dir(cfg.DB), DefaultFileName(cfg.Backend))
+		return nil
+	}
+
+	// Otherwise, use the backend that has been updated most recently.
+	b := backends[len(backends)-1]
+	cfg.Backend = b.name
+	cfg.DB = b.path
+
+	return nil
+}

go/storage/database/database_test.go

@@ -51,3 +51,92 @@ func doTestImpl(t *testing.T, backend string) {
 	genesisTestHelpers.SetTestChainContext()
 	tests.StorageImplementationTests(t, impl, impl, testNs, 0)
 }
+
+func TestAutoBackend(t *testing.T) {
+	t.Run("NoExistingDir", func(t *testing.T) {
+		require := require.New(t)
+
+		tmpDir, err := os.MkdirTemp("", "oasis-storage-database-test")
+		require.NoError(err, "TempDir()")
+		defer os.RemoveAll(tmpDir)
+
+		// When there is no existing database directory, the default should be used.
+		cfg := api.Config{
+			Backend: "auto",
+			DB:      filepath.Join(tmpDir, DefaultFileName("auto")),
+		}
+		impl, err := New(&cfg)
+		require.NoError(err)
+		impl.Cleanup()
+
+		require.Equal("pathbadger", cfg.Backend)
+		require.Equal(filepath.Join(tmpDir, DefaultFileName("pathbadger")), cfg.DB)
+	})
+
+	t.Run("OneExistingDir", func(t *testing.T) {
+		require := require.New(t)
+
+		tmpDir, err := os.MkdirTemp("", "oasis-storage-database-test")
+		require.NoError(err, "TempDir()")
+		defer os.RemoveAll(tmpDir)
+
+		// Create a badger database first.
+		cfg := api.Config{
+			Backend: "badger",
+			DB:      filepath.Join(tmpDir, DefaultFileName("badger")),
+		}
+		impl, err := New(&cfg)
+		require.NoError(err)
+		impl.Cleanup()
+
+		// When there is an existing backend, it should be used.
+		cfg = api.Config{
+			Backend: "auto",
+			DB:      filepath.Join(tmpDir, DefaultFileName("auto")),
+		}
+		impl, err = New(&cfg)
+		require.NoError(err)
+		impl.Cleanup()
+
+		require.Equal("badger", cfg.Backend)
+		require.Equal(filepath.Join(tmpDir, DefaultFileName("badger")), cfg.DB)
+	})
+
+	t.Run("MultiExistingDirs", func(t *testing.T) {
+		require := require.New(t)
+
+		tmpDir, err := os.MkdirTemp("", "oasis-storage-database-test")
+		require.NoError(err, "TempDir()")
+		defer os.RemoveAll(tmpDir)
+
+		// Create a badger database first.
+		cfg := api.Config{
+			Backend: "badger",
+			DB:      filepath.Join(tmpDir, DefaultFileName("badger")),
+		}
+		impl, err := New(&cfg)
+		require.NoError(err)
+		impl.Cleanup()
+
+		// Then create a pathbadger database.
+		cfg = api.Config{
+			Backend: "pathbadger",
+			DB:      filepath.Join(tmpDir, DefaultFileName("pathbadger")),
+		}
+		impl, err = New(&cfg)
+		require.NoError(err)
+		impl.Cleanup()
+
+		// When there are multiple existing backends, the most recent one should be used.
+		cfg = api.Config{
+			Backend: "auto",
+			DB:      filepath.Join(tmpDir, DefaultFileName("auto")),
+		}
+		impl, err = New(&cfg)
+		require.NoError(err)
+		impl.Cleanup()
+
+		require.Equal("pathbadger", cfg.Backend)
+		require.Equal(filepath.Join(tmpDir, DefaultFileName("pathbadger")), cfg.DB)
+	})
+}

go/worker/storage/config/config.go

@@ -35,14 +35,17 @@ type CheckpointerConfig struct {
 
 // Validate validates the configuration settings.
 func (c *Config) Validate() error {
-	_, err := db.GetBackendByName(c.Backend)
-	return err
+	if c.Backend != "auto" {
+		_, err := db.GetBackendByName(c.Backend)
+		return err
+	}
+	return nil
 }
 
 // DefaultConfig returns the default configuration settings.
 func DefaultConfig() Config {
 	return Config{
-		Backend:                "badger",
+		Backend:                "auto",
 		MaxCacheSize:           "64mb",
 		FetcherCount:           4,
 		PublicRPCEnabled:       false,