Write-ahead log repository creationssmh-log-repo-creation

This commits implements write-ahead logging for repository creations.

Repository creations need to be write-ahead logged as well. This is
necessary for a few reasons:

1. The repository creations need to be serialized with other writes
   to avoid bad interactions from concurrency. Gitaly is already
   serializing them by using lock files on the disk. However, as the
   TransactionManager is already serializing writes, it makes sense
   to converge on one approach. This way reads also don't go through before
   the repository is fully created, thus making creations atomic.
2. The creations need to be logged so they can be backed up. This allows
   for the repository to be immediately backed up with WAL archival
   directly from creation.
3. Logging the creations ensures they'll be replicated eventually as part
   of the log when Raft comes around.

6 files changed, 521 insertions, 68 deletions

diff --git a/internal/gitaly/partition_manager.go b/internal/gitaly/partition_manager.go
index 408d5f4a3..83f9c9ec4 100644
--- a/internal/gitaly/partition_manager.go
+++ b/internal/gitaly/partition_manager.go
@@ -9,6 +9,7 @@ import (
 
 	"github.com/dgraph-io/badger/v3"
 	"github.com/sirupsen/logrus"
+	"gitlab.com/gitlab-org/gitaly/v16/internal/git"
 	"gitlab.com/gitlab-org/gitaly/v16/internal/git/localrepo"
 	repo "gitlab.com/gitlab-org/gitaly/v16/internal/git/repository"
 	"gitlab.com/gitlab-org/gitaly/v16/internal/gitaly/config"
@@ -31,6 +32,8 @@ type PartitionManager struct {
 	partitions map[string]*partition
 	// localRepoFactory is used by PartitionManager to construct `localrepo.Repo`.
 	localRepoFactory localrepo.Factory
+	// commandFactory is passed as a dependency to the constructed TransactionManagers.
+	commandFactory git.CommandFactory
 	// logger handles all logging for PartitionManager.
 	logger logrus.FieldLogger
 	// stopped tracks whether the PartitionManager has been stopped. If the manager is stopped,
@@ -61,7 +64,7 @@ type partition struct {
 }
 
 // NewPartitionManager returns a new PartitionManager.
-func NewPartitionManager(db *badger.DB, storages []config.Storage, localRepoFactory localrepo.Factory, logger logrus.FieldLogger, stagingDir string) *PartitionManager {
+func NewPartitionManager(db *badger.DB, storages []config.Storage, localRepoFactory localrepo.Factory, cmdFactory git.CommandFactory, logger logrus.FieldLogger, stagingDir string) *PartitionManager {
 	storagesMap := make(map[string]string, len(storages))
 	for _, storage := range storages {
 		storagesMap[storage.Name] = storage.Path
@@ -71,6 +74,7 @@ func NewPartitionManager(db *badger.DB, storages []config.Storage, localRepoFact
 		db:               db,
 		partitions:       make(map[string]*partition),
 		localRepoFactory: localRepoFactory,
+		commandFactory:   cmdFactory,
 		logger:           logger,
 		stagingDirectory: stagingDir,
 		storages:         storagesMap,
@@ -123,7 +127,7 @@ func (pm *PartitionManager) Begin(ctx context.Context, repo repo.GitRepo) (*Tran
 				return nil, fmt.Errorf("scope by storage: %w", err)
 			}
 
-			mgr := NewTransactionManager(pm.db, storagePath, relativePath, stagingDir, storageScopedFactory, pm.transactionFinalizerFactory(ptn))
+			mgr := NewTransactionManager(pm.db, storagePath, relativePath, stagingDir, storageScopedFactory, pm.commandFactory, pm.transactionFinalizerFactory(ptn))
 			ptn.transactionManager = mgr
 
 			pm.partitions[partitionKey] = ptn
diff --git a/internal/gitaly/partition_manager_test.go b/internal/gitaly/partition_manager_test.go
index aeb26f7e3..39e3e14f3 100644
--- a/internal/gitaly/partition_manager_test.go
+++ b/internal/gitaly/partition_manager_test.go
@@ -433,7 +433,7 @@ func TestPartitionManager(t *testing.T) {
 			stagingDir := filepath.Join(t.TempDir(), "staging")
 			require.NoError(t, os.Mkdir(stagingDir, perm.PrivateDir))
 
-			partitionManager := NewPartitionManager(database, cfg.Storages, localRepoFactory, logrus.StandardLogger(), stagingDir)
+			partitionManager := NewPartitionManager(database, cfg.Storages, localRepoFactory, cmdFactory, logrus.StandardLogger(), stagingDir)
 			defer func() {
 				partitionManager.Stop()
 				// Assert all staging directories have been removed.
diff --git a/internal/gitaly/transaction_manager.go b/internal/gitaly/transaction_manager.go
index ad8159ac1..477296a0e 100644
--- a/internal/gitaly/transaction_manager.go
+++ b/internal/gitaly/transaction_manager.go
@@ -33,6 +33,8 @@ import (
 var (
 	// ErrRepositoryNotFound is returned when the repository doesn't exist.
 	ErrRepositoryNotFound = structerr.NewNotFound("repository not found")
+	// ErrRepositoryAlreadyExists is returned when the repository already exists.
+	ErrRepositoryAlreadyExists = structerr.NewAlreadyExists("repository already exists")
 	// ErrTransactionProcessingStopped is returned when the TransactionManager stops processing transactions.
 	ErrTransactionProcessingStopped = errors.New("transaction processing stopped")
 	// errInitializationFailed is returned when the TransactionManager failed to initialize successfully.
@@ -164,6 +166,9 @@ type Transaction struct {
 	includesPack bool
 	// stagingRepository is a repository that is used to stage the transaction. If there are quarantined
 	// objects, it has the quarantine applied so the objects are available for verification and packing.
+	// Generally the staging repository is the actual repository instance. If the repository doesn't exist
+	// yet, the staging repository is a temporary repository that is deleted once the transaction has been
+	// finished.
 	stagingRepository repository
 
 	// Snapshot contains the details of the Transaction's read snapshot.
@@ -173,6 +178,7 @@ type Transaction struct {
 	referenceUpdates         ReferenceUpdates
 	defaultBranchUpdate      *DefaultBranchUpdate
 	customHooksUpdate        *CustomHooksUpdate
+	repositoryCreation       *gitalypb.LogEntry_RepositoryCreation
 	deleteRepository         bool
 }
 
@@ -181,7 +187,17 @@ type Transaction struct {
 //
 // The returned Transaction's read snapshot includes all writes that were committed prior to the
 // Begin call. Begin blocks until the committed writes have been applied to the repository.
-func (mgr *TransactionManager) Begin(ctx context.Context) (_ *Transaction, returnedErr error) {
+func (mgr *TransactionManager) Begin(ctx context.Context) (*Transaction, error) {
+	return mgr.begin(ctx, true)
+}
+
+// BeginCreation starts a new transaction. It allowas the transaction to start even if the repository
+// doesn't exist. See the documentation for Begin for details on the use.
+func (mgr *TransactionManager) BeginCreation(ctx context.Context) (*Transaction, error) {
+	return mgr.begin(ctx, false)
+}
+
+func (mgr *TransactionManager) begin(ctx context.Context, repositoryShouldExist bool) (_ *Transaction, returnedErr error) {
 	// Wait until the manager has been initialized so the notification channels
 	// and the log indexes are loaded.
 	select {
@@ -194,9 +210,9 @@ func (mgr *TransactionManager) Begin(ctx context.Context) (_ *Transaction, retur
 	}
 
 	mgr.mutex.Lock()
-	if !mgr.repositoryExists {
+	if err := mgr.verifyRepositoryExistence(repositoryShouldExist); err != nil {
 		mgr.mutex.Unlock()
-		return nil, ErrRepositoryNotFound
+		return nil, err
 	}
 
 	txn := &Transaction{
@@ -221,6 +237,10 @@ func (mgr *TransactionManager) Begin(ctx context.Context) (_ *Transaction, retur
 	}
 
 	txn.initStagingDirectory = func() error {
+		if txn.stagingDirectory != "" {
+			return nil
+		}
+
 		stagingDirectory, err := os.MkdirTemp(mgr.stagingDirectory, "")
 		if err != nil {
 			return fmt.Errorf("mkdir temp: %w", err)
@@ -264,6 +284,16 @@ func (mgr *TransactionManager) Begin(ctx context.Context) (_ *Transaction, retur
 	}
 }
 
+func (mgr *TransactionManager) verifyRepositoryExistence(shouldExist bool) error {
+	if shouldExist && !mgr.repositoryExists {
+		return ErrRepositoryNotFound
+	} else if !shouldExist && mgr.repositoryExists {
+		return ErrRepositoryAlreadyExists
+	}
+
+	return nil
+}
+
 // Commit performs the changes. If no error is returned, the transaction was successful and the changes
 // have been performed. If an error was returned, the transaction may or may not be persisted.
 func (txn *Transaction) Commit(ctx context.Context) (returnedErr error) {
@@ -317,6 +347,13 @@ func (txn *Transaction) UpdateReferences(updates ReferenceUpdates) {
 	txn.referenceUpdates = updates
 }
 
+// CreateRepository creates the repository with the specified object format when the transaction commits.
+func (txn *Transaction) CreateRepository(objectFormat git.ObjectHash) {
+	txn.repositoryCreation = &gitalypb.LogEntry_RepositoryCreation{
+		ObjectFormat: objectFormat.ProtoFormat,
+	}
+}
+
 // DeleteRepository deletes the repository when the transaction is committed.
 func (txn *Transaction) DeleteRepository() {
 	txn.deleteRepository = true
@@ -416,7 +453,10 @@ type TransactionManager struct {
 	// left around after crashes. The files are temporary and any leftover files are expected to be cleaned up when
 	// Gitaly starts.
 	stagingDirectory string
-
+	// commandFactory is used to spawn git commands without a repository.
+	commandFactory git.CommandFactory
+	// repositoryFactory is used to build a localrepo.Repo for operations that need it.
+	repositoryFactory localrepo.StorageScopedFactory
 	// repositoryExists marks whether the repository exists or not. The repository may not exist if it has
 	// never been created, or if it has been deleted.
 	repositoryExists bool
@@ -424,6 +464,8 @@ type TransactionManager struct {
 	repository repository
 	// repositoryPath is the path to the repository this TransactionManager is acting on.
 	repositoryPath string
+	// storagePath is the absolute path to this storage this TransactionManager is operating on.
+	storagePath string
 	// relativePath is the repository's relative path inside the storage.
 	relativePath string
 	// db is the handle to the key-value store used for storing the write-ahead log related state.
@@ -470,7 +512,7 @@ type repository interface {
 }
 
 // NewTransactionManager returns a new TransactionManager for the given repository.
-func NewTransactionManager(db *badger.DB, storagePath, relativePath, stagingDir string, repositoryFactory localrepo.StorageScopedFactory, transactionFinalizer func()) *TransactionManager {
+func NewTransactionManager(db *badger.DB, storagePath, relativePath, stagingDir string, repositoryFactory localrepo.StorageScopedFactory, cmdFactory git.CommandFactory, transactionFinalizer func()) *TransactionManager {
 	ctx, cancel := context.WithCancel(context.Background())
 	return &TransactionManager{
 		ctx:                  ctx,
@@ -479,6 +521,7 @@ func NewTransactionManager(db *badger.DB, storagePath, relativePath, stagingDir
 		stop:                 cancel,
 		repository:           repositoryFactory.Build(relativePath),
 		repositoryPath:       filepath.Join(storagePath, relativePath),
+		storagePath:          storagePath,
 		relativePath:         relativePath,
 		db:                   newDatabaseAdapter(db),
 		admissionQueue:       make(chan *Transaction),
@@ -486,6 +529,8 @@ func NewTransactionManager(db *badger.DB, storagePath, relativePath, stagingDir
 		initialized:          make(chan struct{}),
 		applyNotifications:   make(map[LogIndex]chan struct{}),
 		stagingDirectory:     stagingDir,
+		commandFactory:       cmdFactory,
+		repositoryFactory:    repositoryFactory,
 		transactionFinalizer: transactionFinalizer,
 	}
 }
@@ -531,6 +576,25 @@ func (mgr *TransactionManager) setupStagingRepository(ctx context.Context, trans
 	// If the repository exists, we use it for staging the transaction.
 	transaction.stagingRepository = mgr.repository
 
+	if transaction.repositoryCreation != nil {
+		// Git requires that certain commands like 'pack-objects' and 'rev-list' are ran in a repository.
+		// Providing just an object directory does not suffice. If the repository doesn't exist yet, we create
+		// a temporary repository that we use to stage the transaction. The staging repository is used to run the
+		// commands that require a repository. The reference updates in the transaction will also be verified
+		// against temporary staging repository. After the transaction is logged, the staging repository
+		// is removed, and the actual repository will be created when the log entry is applied.
+		if err := transaction.initStagingDirectory(); err != nil {
+			return fmt.Errorf("init staging directory: %w", err)
+		}
+
+		stagingRepositoryRelativePath := filepath.Join(strings.TrimPrefix(transaction.stagingDirectory, mgr.storagePath+"/"), "repository")
+		if err := mgr.createRepository(ctx, filepath.Join(transaction.stagingDirectory, "repository"), transaction.repositoryCreation.ObjectFormat); err != nil {
+			return fmt.Errorf("create staging repository: %w", err)
+		}
+
+		transaction.stagingRepository = mgr.repositoryFactory.Build(stagingRepositoryRelativePath)
+	}
+
 	// If the transaction has a quarantine directory, we must use it when staging the pack
 	// file and verifying the references so the objects are available.
 	if transaction.quarantineDirectory != "" {
@@ -701,12 +765,22 @@ func (mgr *TransactionManager) processTransaction() (returnedErr error) {
 	}
 
 	transaction.result <- func() (commitErr error) {
-		if !mgr.repositoryExists {
+		logEntry := &gitalypb.LogEntry{}
+
+		if transaction.repositoryCreation != nil {
+			if mgr.repositoryExists {
+				return ErrRepositoryAlreadyExists
+			}
+
+			if err := os.MkdirAll(filepath.Join(mgr.repositoryPath, "wal", "packs"), fs.ModePerm); err != nil {
+				return fmt.Errorf("create repository directory: %w", err)
+			}
+
+			logEntry.RepositoryCreation = transaction.repositoryCreation
+		} else if !mgr.repositoryExists {
 			return ErrRepositoryNotFound
 		}
 
-		logEntry := &gitalypb.LogEntry{}
-
 		var err error
 		logEntry.ReferenceUpdates, err = mgr.verifyReferences(mgr.ctx, transaction)
 		if err != nil {
@@ -1156,6 +1230,10 @@ func (mgr *TransactionManager) appendLogEntry(nextLogIndex LogIndex, logEntry *g
 		mgr.hookIndex = nextLogIndex
 	}
 	mgr.applyNotifications[nextLogIndex] = make(chan struct{})
+	if logEntry.RepositoryCreation != nil {
+		mgr.repositoryExists = true
+	}
+
 	if logEntry.RepositoryDeletion != nil {
 		mgr.repositoryExists = false
 		mgr.hookIndex = 0
@@ -1180,6 +1258,10 @@ func (mgr *TransactionManager) applyLogEntry(ctx context.Context, logIndex LogIn
 			return fmt.Errorf("apply repository deletion: %w", err)
 		}
 	} else {
+		if err := mgr.applyRepositoryCreation(ctx, logEntry.RepositoryCreation); err != nil {
+			return fmt.Errorf("apply repository deletion: %w", err)
+		}
+
 		if logEntry.IncludesPack {
 			if err := mgr.applyPackFile(ctx, logIndex); err != nil {
 				return fmt.Errorf("apply pack file: %w", err)
@@ -1229,6 +1311,55 @@ func (mgr *TransactionManager) applyLogEntry(ctx context.Context, logIndex LogIn
 	return nil
 }
 
+// applyRepositoryCreation applies a repository creation by creating a repository.
+func (mgr *TransactionManager) applyRepositoryCreation(ctx context.Context, entry *gitalypb.LogEntry_RepositoryCreation) error {
+	if entry == nil {
+		return nil
+	}
+
+	if err := mgr.createRepository(ctx, mgr.repositoryPath, entry.ObjectFormat); err != nil {
+		return fmt.Errorf("create repository: %w", err)
+	}
+
+	if err := mgr.createDirectories(); err != nil {
+		return fmt.Errorf("create directories: %w", err)
+	}
+
+	// Sync the parent directory. We expect that git syncs its own writes.
+	if err := safe.NewSyncer().Sync(filepath.Dir(mgr.repositoryPath)); err != nil {
+		return fmt.Errorf("sync: %w", err)
+	}
+
+	return nil
+}
+
+func (mgr *TransactionManager) createRepository(ctx context.Context, repositoryPath string, objectFormat gitalypb.ObjectFormat) error {
+	objectHash, err := git.ObjectHashByProto(objectFormat)
+	if err != nil {
+		return fmt.Errorf("object hash by proto: %w", err)
+	}
+
+	stderr := &bytes.Buffer{}
+	cmd, err := mgr.commandFactory.NewWithoutRepo(ctx, git.Command{
+		Name: "init",
+		Flags: []git.Option{
+			git.Flag{Name: "--bare"},
+			git.Flag{Name: "--quiet"},
+			git.Flag{Name: "--object-format=" + objectHash.Format},
+		},
+		Args: []string{repositoryPath},
+	}, git.WithStderr(stderr))
+	if err != nil {
+		return fmt.Errorf("spawn git init: %w", err)
+	}
+
+	if err := cmd.Wait(); err != nil {
+		return structerr.New("wait git init: %w", err).WithMetadata("stderr", stderr.String())
+	}
+
+	return nil
+}
+
 // applyRepositoryDeletion deletes the repository.
 //
 // Given how the repositories are laid out in the storage, we currently can't support MVCC for them.
diff --git a/internal/gitaly/transaction_manager_test.go b/internal/gitaly/transaction_manager_test.go
index 4f5ad8ace..43b38b1ee 100644
--- a/internal/gitaly/transaction_manager_test.go
+++ b/internal/gitaly/transaction_manager_test.go
@@ -131,6 +131,7 @@ func TestTransactionManager(t *testing.T) {
 	type testSetup struct {
 		Config            config.Cfg
 		RepositoryFactory localrepo.StorageScopedFactory
+		CommandFactory    git.CommandFactory
 		ObjectHash        git.ObjectHash
 		NonExistentOID    git.ObjectID
 		Commits           testCommits
@@ -194,6 +195,7 @@ func TestTransactionManager(t *testing.T) {
 			Config:            cfg,
 			ObjectHash:        objectHash,
 			RepositoryFactory: repositoryFactory,
+			CommandFactory:    cmdFactory,
 			NonExistentOID:    nonExistentOID,
 			Commits: testCommits{
 				First: testCommit{
@@ -266,6 +268,8 @@ func TestTransactionManager(t *testing.T) {
 		// TransactionID is the identifier given to the transaction created. This is used to identify
 		// the transaction in later steps.
 		TransactionID int
+
+		AllowNonExistent bool
 		// Context is the context to use for the Begin call.
 		Context context.Context
 		// ExpectedSnapshot is the expected snapshot of the transaction.
@@ -295,6 +299,8 @@ func TestTransactionManager(t *testing.T) {
 		CustomHooksUpdate *CustomHooksUpdate
 		// DeleteRepository deletes the repository on commit.
 		DeleteRepository bool
+		// CreateRepository creates the repository on commit.
+		CreateRepository bool
 	}
 
 	// Rollback calls Rollback on a transaction.
@@ -2611,6 +2617,209 @@ func TestTransactionManager(t *testing.T) {
 				RepositoryDoesntExist: true,
 			},
 		},
+		{
+			desc: "create repository when it doesn't exist",
+			steps: steps{
+				RemoveRepository{},
+				StartManager{},
+				Begin{
+					AllowNonExistent: true,
+				},
+				Commit{
+					CreateRepository: true,
+				},
+			},
+			expectedState: StateAssertion{
+				Database: DatabaseState{
+					string(keyAppliedLogIndex(relativePath)): LogIndex(1).toProto(),
+				},
+				Objects: []git.ObjectID{},
+			},
+		},
+		{
+			desc: "create repository when it already exists",
+			steps: steps{
+				RemoveRepository{},
+				StartManager{},
+				Begin{
+					TransactionID:    1,
+					AllowNonExistent: true,
+				},
+				Commit{
+					TransactionID:    1,
+					CreateRepository: true,
+				},
+				Begin{
+					TransactionID:    2,
+					AllowNonExistent: true,
+					ExpectedError:    ErrRepositoryAlreadyExists,
+				},
+			},
+			expectedState: StateAssertion{
+				Database: DatabaseState{
+					string(keyAppliedLogIndex(relativePath)): LogIndex(1).toProto(),
+				},
+				Objects: []git.ObjectID{},
+			},
+		},
+		{
+			desc: "create repository with interleaved creations",
+			steps: steps{
+				RemoveRepository{},
+				StartManager{},
+				Begin{
+					TransactionID:    1,
+					AllowNonExistent: true,
+				},
+				Begin{
+					TransactionID:    2,
+					AllowNonExistent: true,
+				},
+				Commit{
+					TransactionID:    1,
+					CreateRepository: true,
+				},
+				Commit{
+					TransactionID:    2,
+					CreateRepository: true,
+					ExpectedError:    ErrRepositoryAlreadyExists,
+				},
+			},
+			expectedState: StateAssertion{
+				Database: DatabaseState{
+					string(keyAppliedLogIndex(relativePath)): LogIndex(1).toProto(),
+				},
+				Objects: []git.ObjectID{},
+			},
+		},
+		{
+			desc: "create repository again after deletion",
+			steps: steps{
+				RemoveRepository{},
+				StartManager{},
+				Begin{
+					TransactionID:    1,
+					AllowNonExistent: true,
+				},
+				Commit{
+					TransactionID:    1,
+					CreateRepository: true,
+				},
+				Begin{
+					TransactionID: 2,
+					ExpectedSnapshot: Snapshot{
+						ReadIndex: 1,
+					},
+				},
+				Commit{
+					TransactionID: 2,
+					ReferenceUpdates: ReferenceUpdates{
+						"refs/heads/main": {OldOID: setup.ObjectHash.ZeroOID, NewOID: setup.Commits.First.OID},
+					},
+					QuarantinedPacks: [][]byte{setup.Commits.First.Pack},
+					CustomHooksUpdate: &CustomHooksUpdate{
+						CustomHooksTAR: validCustomHooks(t),
+					},
+				},
+				Begin{
+					TransactionID: 3,
+					ExpectedSnapshot: Snapshot{
+						ReadIndex: 2,
+						HookIndex: 2,
+					},
+				},
+				Commit{
+					TransactionID:    3,
+					DeleteRepository: true,
+				},
+				Begin{
+					TransactionID:    4,
+					AllowNonExistent: true,
+					ExpectedSnapshot: Snapshot{
+						ReadIndex: 3,
+					},
+				},
+				Commit{
+					TransactionID:    4,
+					CreateRepository: true,
+				},
+				Begin{
+					TransactionID: 5,
+					ExpectedSnapshot: Snapshot{
+						ReadIndex: 4,
+					},
+				},
+				Rollback{
+					TransactionID: 5,
+				},
+			},
+			expectedState: StateAssertion{
+				Database: DatabaseState{
+					string(keyAppliedLogIndex(relativePath)): LogIndex(4).toProto(),
+				},
+				Objects: []git.ObjectID{},
+			},
+		},
+		{
+			desc: "create repository with full state",
+			steps: steps{
+				RemoveRepository{},
+				StartManager{},
+				Begin{
+					AllowNonExistent: true,
+				},
+				Commit{
+					CreateRepository: true,
+					ReferenceUpdates: ReferenceUpdates{
+						"refs/heads/main":   {OldOID: setup.ObjectHash.ZeroOID, NewOID: setup.Commits.First.OID},
+						"refs/heads/branch": {OldOID: setup.ObjectHash.ZeroOID, NewOID: setup.Commits.Second.OID},
+					},
+					QuarantinedPacks: [][]byte{setup.Commits.First.Pack, setup.Commits.Second.Pack},
+					DefaultBranchUpdate: &DefaultBranchUpdate{
+						Reference: "refs/heads/branch",
+					},
+					CustomHooksUpdate: &CustomHooksUpdate{
+						CustomHooksTAR: validCustomHooks(t),
+					},
+				},
+			},
+			expectedState: StateAssertion{
+				DefaultBranch: "refs/heads/branch",
+				References: []git.Reference{
+					{Name: "refs/heads/main", Target: setup.Commits.First.OID.String()},
+					{Name: "refs/heads/branch", Target: setup.Commits.Second.OID.String()},
+				},
+				Database: DatabaseState{
+					string(keyAppliedLogIndex(relativePath)): LogIndex(1).toProto(),
+				},
+				Directory: testhelper.DirectoryState{
+					"/wal":       {Mode: umask.Mask(fs.ModeDir | fs.ModePerm)},
+					"/wal/packs": {Mode: umask.Mask(fs.ModeDir | fs.ModePerm)},
+					"/wal/packs/1.pack": packFileDirectoryEntry(
+						setup.Config,
+						umask.Mask(perm.PrivateFile),
+						[]git.ObjectID{
+							setup.ObjectHash.EmptyTreeOID,
+							setup.Commits.First.OID,
+							setup.Commits.Second.OID,
+						},
+					),
+					"/wal/hooks":   {Mode: umask.Mask(fs.ModeDir | fs.ModePerm)},
+					"/wal/hooks/1": {Mode: umask.Mask(fs.ModeDir | fs.ModePerm)},
+					"/wal/hooks/1/pre-receive": {
+						Mode:    umask.Mask(fs.ModePerm),
+						Content: []byte("hook content"),
+					},
+					"/wal/hooks/1/private-dir":              {Mode: umask.Mask(fs.ModeDir | perm.PrivateDir)},
+					"/wal/hooks/1/private-dir/private-file": {Mode: umask.Mask(perm.PrivateFile), Content: []byte("private content")},
+				},
+				Objects: []git.ObjectID{
+					setup.ObjectHash.EmptyTreeOID,
+					setup.Commits.First.OID,
+					setup.Commits.Second.OID,
+				},
+			},
+		},
 	}
 
 	type invalidReferenceTestCase struct {
@@ -2745,14 +2954,15 @@ func TestTransactionManager(t *testing.T) {
 			require.NoError(t, err)
 			defer testhelper.MustClose(t, database)
 
-			stagingDir := t.TempDir()
+			stagingDir := filepath.Join(setup.Config.Storages[0].Path, "staging")
+			require.NoError(t, os.MkdirAll(stagingDir, perm.PrivateDir))
 			storagePath := setup.Config.Storages[0].Path
 
 			var (
 				// managerRunning tracks whether the manager is running or stopped.
 				managerRunning bool
 				// transactionManager is the current TransactionManager instance.
-				transactionManager = NewTransactionManager(database, storagePath, relativePath, stagingDir, setup.RepositoryFactory, noopTransactionFinalizer)
+				transactionManager = NewTransactionManager(database, storagePath, relativePath, stagingDir, setup.RepositoryFactory, setup.CommandFactory, noopTransactionFinalizer)
 				// managerErr is used for synchronizing manager stopping and returning
 				// the error from Run.
 				managerErr chan error
@@ -2793,7 +3003,7 @@ func TestTransactionManager(t *testing.T) {
 					managerRunning = true
 					managerErr = make(chan error)
 
-					transactionManager = NewTransactionManager(database, storagePath, relativePath, stagingDir, setup.RepositoryFactory, noopTransactionFinalizer)
+					transactionManager = NewTransactionManager(database, storagePath, relativePath, stagingDir, setup.RepositoryFactory, setup.CommandFactory, noopTransactionFinalizer)
 					installHooks(t, transactionManager, database, hooks{
 						beforeReadLogEntry:    step.Hooks.BeforeApplyLogEntry,
 						beforeResolveRevision: step.Hooks.BeforeAppendLogEntry,
@@ -2835,7 +3045,15 @@ func TestTransactionManager(t *testing.T) {
 						beginCtx = step.Context
 					}
 
-					transaction, err := transactionManager.Begin(beginCtx)
+					var transaction *Transaction
+					var err error
+
+					if step.AllowNonExistent {
+						transaction, err = transactionManager.BeginCreation(beginCtx)
+					} else {
+						transaction, err = transactionManager.Begin(beginCtx)
+					}
+
 					require.Equal(t, step.ExpectedError, err)
 					if err == nil {
 						require.Equal(t, step.ExpectedSnapshot, transaction.Snapshot())
@@ -2887,6 +3105,10 @@ func TestTransactionManager(t *testing.T) {
 						transaction.DeleteRepository()
 					}
 
+					if step.CreateRepository {
+						transaction.CreateRepository(setup.ObjectHash)
+					}
+
 					commitCtx := ctx
 					if step.Context != nil {
 						commitCtx = step.Context
@@ -3101,7 +3323,7 @@ func BenchmarkTransactionManager(b *testing.B) {
 				commit1 = gittest.WriteCommit(b, cfg, repoPath, gittest.WithParents())
 				commit2 = gittest.WriteCommit(b, cfg, repoPath, gittest.WithParents(commit1))
 
-				manager := NewTransactionManager(database, cfg.Storages[0].Path, repo.RelativePath, b.TempDir(), repositoryFactory, noopTransactionFinalizer)
+				manager := NewTransactionManager(database, cfg.Storages[0].Path, repo.RelativePath, b.TempDir(), repositoryFactory, cmdFactory, noopTransactionFinalizer)
 				managers = append(managers, manager)
 
 				managerWG.Add(1)
diff --git a/proto/go/gitalypb/log.pb.go b/proto/go/gitalypb/log.pb.go
index 3ed22d282..8d2f8db00 100644
--- a/proto/go/gitalypb/log.pb.go
+++ b/proto/go/gitalypb/log.pb.go
@@ -43,6 +43,8 @@ type LogEntry struct {
 	IncludesPack bool `protobuf:"varint,4,opt,name=includes_pack,json=includesPack,proto3" json:"includes_pack,omitempty"`
 	// RepositoryDeletion, when set, indicates this log entry deletes the repository.
 	RepositoryDeletion *LogEntry_RepositoryDeletion `protobuf:"bytes,5,opt,name=repository_deletion,json=repositoryDeletion,proto3" json:"repository_deletion,omitempty"`
+	// repository_creation is set if this log entry creates a repository.
+	RepositoryCreation *LogEntry_RepositoryCreation `protobuf:"bytes,6,opt,name=repository_creation,json=repositoryCreation,proto3" json:"repository_creation,omitempty"`
 }
 
 func (x *LogEntry) Reset() {
@@ -112,6 +114,13 @@ func (x *LogEntry) GetRepositoryDeletion() *LogEntry_RepositoryDeletion {
 	return nil
 }
 
+func (x *LogEntry) GetRepositoryCreation() *LogEntry_RepositoryCreation {
+	if x != nil {
+		return x.RepositoryCreation
+	}
+	return nil
+}
+
 // LogIndex serializes a log index. It's used for storing a repository's
 // applied log index in the database.
 //
@@ -366,56 +375,116 @@ func (*LogEntry_RepositoryDeletion) Descriptor() ([]byte, []int) {
 	return file_log_proto_rawDescGZIP(), []int{0, 3}
 }
 
+// RepositoryCreation models a log entry that creates a repository.
+type LogEntry_RepositoryCreation struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	// object_format defines the object format to use for the repository.
+	ObjectFormat ObjectFormat `protobuf:"varint,1,opt,name=object_format,json=objectFormat,proto3,enum=gitaly.ObjectFormat" json:"object_format,omitempty"`
+}
+
+func (x *LogEntry_RepositoryCreation) Reset() {
+	*x = LogEntry_RepositoryCreation{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_log_proto_msgTypes[6]
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		ms.StoreMessageInfo(mi)
+	}
+}
+
+func (x *LogEntry_RepositoryCreation) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*LogEntry_RepositoryCreation) ProtoMessage() {}
+
+func (x *LogEntry_RepositoryCreation) ProtoReflect() protoreflect.Message {
+	mi := &file_log_proto_msgTypes[6]
+	if protoimpl.UnsafeEnabled && x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use LogEntry_RepositoryCreation.ProtoReflect.Descriptor instead.
+func (*LogEntry_RepositoryCreation) Descriptor() ([]byte, []int) {
+	return file_log_proto_rawDescGZIP(), []int{0, 4}
+}
+
+func (x *LogEntry_RepositoryCreation) GetObjectFormat() ObjectFormat {
+	if x != nil {
+		return x.ObjectFormat
+	}
+	return ObjectFormat_OBJECT_FORMAT_UNSPECIFIED
+}
+
 var File_log_proto protoreflect.FileDescriptor
 
 var file_log_proto_rawDesc = []byte{
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+	0x70, 0x62, 0x62, 0x06, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x33,
 }
 
 var (
@@ -430,7 +499,7 @@ func file_log_proto_rawDescGZIP() []byte {
 	return file_log_proto_rawDescData
 }
 
-var file_log_proto_msgTypes = make([]protoimpl.MessageInfo, 6)
+var file_log_proto_msgTypes = make([]protoimpl.MessageInfo, 7)
 var file_log_proto_goTypes = []interface{}{
 	(*LogEntry)(nil),                     // 0: gitaly.LogEntry
 	(*LogIndex)(nil),                     // 1: gitaly.LogIndex
@@ -438,17 +507,21 @@ var file_log_proto_goTypes = []interface{}{
 	(*LogEntry_DefaultBranchUpdate)(nil), // 3: gitaly.LogEntry.DefaultBranchUpdate
 	(*LogEntry_CustomHooksUpdate)(nil),   // 4: gitaly.LogEntry.CustomHooksUpdate
 	(*LogEntry_RepositoryDeletion)(nil),  // 5: gitaly.LogEntry.RepositoryDeletion
+	(*LogEntry_RepositoryCreation)(nil),  // 6: gitaly.LogEntry.RepositoryCreation
+	(ObjectFormat)(0),                    // 7: gitaly.ObjectFormat
 }
 var file_log_proto_depIdxs = []int32{
 	2, // 0: gitaly.LogEntry.reference_updates:type_name -> gitaly.LogEntry.ReferenceUpdate
 	3, // 1: gitaly.LogEntry.default_branch_update:type_name -> gitaly.LogEntry.DefaultBranchUpdate
 	4, // 2: gitaly.LogEntry.custom_hooks_update:type_name -> gitaly.LogEntry.CustomHooksUpdate
 	5, // 3: gitaly.LogEntry.repository_deletion:type_name -> gitaly.LogEntry.RepositoryDeletion
-	4, // [4:4] is the sub-list for method output_type
-	4, // [4:4] is the sub-list for method input_type
-	4, // [4:4] is the sub-list for extension type_name
-	4, // [4:4] is the sub-list for extension extendee
-	0, // [0:4] is the sub-list for field type_name
+	6, // 4: gitaly.LogEntry.repository_creation:type_name -> gitaly.LogEntry.RepositoryCreation
+	7, // 5: gitaly.LogEntry.RepositoryCreation.object_format:type_name -> gitaly.ObjectFormat
+	6, // [6:6] is the sub-list for method output_type
+	6, // [6:6] is the sub-list for method input_type
+	6, // [6:6] is the sub-list for extension type_name
+	6, // [6:6] is the sub-list for extension extendee
+	0, // [0:6] is the sub-list for field type_name
 }
 
 func init() { file_log_proto_init() }
@@ -456,6 +529,7 @@ func file_log_proto_init() {
 	if File_log_proto != nil {
 		return
 	}
+	file_shared_proto_init()
 	if !protoimpl.UnsafeEnabled {
 		file_log_proto_msgTypes[0].Exporter = func(v interface{}, i int) interface{} {
 			switch v := v.(*LogEntry); i {
@@ -529,6 +603,18 @@ func file_log_proto_init() {
 				return nil
 			}
 		}
+		file_log_proto_msgTypes[6].Exporter = func(v interface{}, i int) interface{} {
+			switch v := v.(*LogEntry_RepositoryCreation); i {
+			case 0:
+				return &v.state
+			case 1:
+				return &v.sizeCache
+			case 2:
+				return &v.unknownFields
+			default:
+				return nil
+			}
+		}
 	}
 	type x struct{}
 	out := protoimpl.TypeBuilder{
@@ -536,7 +622,7 @@ func file_log_proto_init() {
 			GoPackagePath: reflect.TypeOf(x{}).PkgPath(),
 			RawDescriptor: file_log_proto_rawDesc,
 			NumEnums:      0,
-			NumMessages:   6,
+			NumMessages:   7,
 			NumExtensions: 0,
 			NumServices:   0,
 		},
diff --git a/proto/log.proto b/proto/log.proto
index 15b031c54..564ddd1a1 100644
--- a/proto/log.proto
+++ b/proto/log.proto
@@ -2,6 +2,8 @@ syntax = "proto3";
 
 package gitaly;
 
+import "shared.proto";
+
 option go_package = "gitlab.com/gitlab-org/gitaly/v16/proto/go/gitalypb";
 
 // LogEntry is a single entry in a repository's write-ahead log.
@@ -39,6 +41,12 @@ message LogEntry {
   message RepositoryDeletion {
   }
 
+  // RepositoryCreation models a log entry that creates a repository.
+  message RepositoryCreation {
+    // object_format defines the object format to use for the repository.
+    ObjectFormat object_format = 1;
+  }
+
   // reference_updates contains the reference updates this log
   // entry records. The logged reference updates have already passed
   // through verification and are applied without any further checks.
@@ -53,6 +61,8 @@ message LogEntry {
   bool includes_pack = 4;
   // RepositoryDeletion, when set, indicates this log entry deletes the repository.
   RepositoryDeletion repository_deletion = 5;
+  // repository_creation is set if this log entry creates a repository.
+  RepositoryCreation repository_creation = 6;
 }
 
 // LogIndex serializes a log index. It's used for storing a repository's