dnote · sungwoncho · Oct 26, 2025 · Oct 26, 2025 · Oct 26, 2025
diff --git a/pkg/cli/database/testutils.go b/pkg/cli/database/testutils.go
@@ -63,7 +63,8 @@ func InitTestMemoryDB(t *testing.T) *DB {
 
 // InitTestFileDB initializes a file-based test database with the default schema.
 func InitTestFileDB(t *testing.T) (*DB, string) {
-	dbPath := filepath.Join(t.TempDir(), "dnote.db")
+	uuid := mustGenerateTestUUID(t)
+	dbPath := filepath.Join(t.TempDir(), fmt.Sprintf("dnote-%s.db", uuid))
 	db := InitTestFileDBRaw(t, dbPath)
 	return db, dbPath
 }

diff --git a/pkg/e2e/sync/edge_cases_test.go b/pkg/e2e/sync/edge_cases_test.go
@@ -19,13 +19,15 @@
 package sync
 
 import (
+	"io"
 	"testing"
 
 	"github.com/dnote/dnote/pkg/assert"
 	"github.com/dnote/dnote/pkg/cli/consts"
 	cliDatabase "github.com/dnote/dnote/pkg/cli/database"
 	clitest "github.com/dnote/dnote/pkg/cli/testutils"
 	"github.com/google/uuid"
+	"github.com/pkg/errors"
 )
 
 // TestSync_EmptyFragmentPreservesLastMaxUSN verifies that last_max_usn is not reset to 0
@@ -71,3 +73,94 @@ func TestSync_EmptyFragmentPreservesLastMaxUSN(t *testing.T) {
 
 	assert.Equal(t, lastMaxUSN, 3, "last_max_usn should be 3 after syncing")
 }
+
+// TestSync_ConcurrentInitialSync reproduces the issue where two clients with identical
+// local data syncing simultaneously to an empty server results in 500 errors.
+//
+// This demonstrates the race condition:
+// - Client1 starts sync to empty server, gets empty server state
+// - Client2 syncs.
+// - Client1 tries to create same books → 409 "duplicate"
+// - Client1 tries to create notes with wrong UUIDs → 500 "record not found"
+// - stepSync recovers by renaming local books with _2 suffix
+func TestSync_ConcurrentInitialSync(t *testing.T) {
+	env := setupTestEnv(t)
+
+	user := setupUserAndLogin(t, env)
+
+	// Step 1: Create local data and sync
+	clitest.RunDnoteCmd(t, env.CmdOpts, cliBinaryName, "add", "javascript", "-c", "js note from client1")
+	clitest.RunDnoteCmd(t, env.CmdOpts, cliBinaryName, "sync")
+	checkState(t, env.DB, user, env.ServerDB, systemState{
+		clientNoteCount:  1,
+		clientBookCount:  1,
+		clientLastMaxUSN: 2,
+		clientLastSyncAt: serverTime.Unix(),
+		serverNoteCount:  1,
+		serverBookCount:  1,
+		serverUserMaxUSN: 2,
+	})
+
+	// Step 2: Switch to new empty server to simulate concurrent initial sync scenario
+	switchToEmptyServer(t, &env)
+	user = setupUserAndLogin(t, env)
+
+	// Set up client2 with separate database
+	client2DB, client2DBPath := cliDatabase.InitTestFileDB(t)
+	login(t, client2DB, env.ServerDB, user)
+	client2DB.Close() // Close so CLI can access the database
+
+	// Step 3: Client1 syncs to empty server, but during sync Client2 uploads same data
+	// This simulates the race condition deterministically
+	raceCallback := func(stdout io.Reader, stdin io.WriteCloser) error {
+		// Wait for empty server prompt to ensure Client1 has called GetSyncState
+		clitest.MustWaitForPrompt(t, stdout, clitest.PromptEmptyServer)
+
+		// Now Client2 creates the same book and note via CLI (creating the race condition)
+		clitest.RunDnoteCmd(t, env.CmdOpts, cliBinaryName, "--dbPath", client2DBPath, "add", "javascript", "-c", "js note from client2")
+		clitest.RunDnoteCmd(t, env.CmdOpts, cliBinaryName, "--dbPath", client2DBPath, "sync")
+
+		// User confirms sync
+		if _, err := io.WriteString(stdin, "y\n"); err != nil {
+			return errors.Wrap(err, "confirming sync")
+		}
+
+		return nil
+	}
+
+	// Client1 continues sync - will hit 409 conflict, then 500 error, then recover
+	clitest.MustWaitDnoteCmd(t, env.CmdOpts, raceCallback, cliBinaryName, "sync")
+
+	// After sync:
+	// - Server has 2 books: "javascript" (from client2) and "javascript_2" (from client1 renamed)
+	// - Server has 2 notes
+	// - Both clients should converge to the same state
+	expectedState := systemState{
+		clientNoteCount:  2, // both notes
+		clientBookCount:  2, // javascript and javascript_2
+		clientLastMaxUSN: 4, // 2 books + 2 notes
+		clientLastSyncAt: serverTime.Unix(),
+		serverNoteCount:  2,
+		serverBookCount:  2,
+		serverUserMaxUSN: 4,
+	}
+	checkState(t, env.DB, user, env.ServerDB, expectedState)
+
+	// Client2 syncs again to download client1's data
+	clitest.RunDnoteCmd(t, env.CmdOpts, cliBinaryName, "--dbPath", client2DBPath, "sync")
+	client2DB = clitest.MustOpenDatabase(t, client2DBPath)
+	defer client2DB.Close()
+
+	// Client2 should have converged to the same state as client1
+	checkState(t, client2DB, user, env.ServerDB, expectedState)
+
+	// Verify no orphaned notes on server
+	var orphanedCount int
+	if err := env.ServerDB.Raw(`
+		SELECT COUNT(*) FROM notes
+		WHERE book_uuid NOT IN (SELECT uuid FROM books)
+	`).Scan(&orphanedCount).Error; err != nil {
+		t.Fatal(err)
+	}
+	assert.Equal(t, orphanedCount, 0, "server should have no orphaned notes after sync")
+}
diff --git a/pkg/server/app/books.go b/pkg/server/app/books.go
@@ -37,6 +37,7 @@ func (a *App) CreateBook(user database.User, name string) (database.Book, error)
 
 	uuid, err := helpers.GenUUID()
 	if err != nil {
+		tx.Rollback()
 		return database.Book{}, err
 	}
 

diff --git a/pkg/server/app/notes.go b/pkg/server/app/notes.go
@@ -55,6 +55,7 @@ func (a *App) CreateNote(user database.User, bookUUID, content string, addedOn *
 
 	uuid, err := helpers.GenUUID()
 	if err != nil {
+		tx.Rollback()
 		return database.Note{}, err
 	}
 

diff --git a/pkg/server/app/users.go b/pkg/server/app/users.go
@@ -66,9 +66,11 @@ func (a *App) CreateUser(email, password string, passwordConfirmation string) (d
 
 	var count int64
 	if err := tx.Model(&database.User{}).Where("email = ?", email).Count(&count).Error; err != nil {
+		tx.Rollback()
 		return database.User{}, pkgErrors.Wrap(err, "counting user")
 	}
 	if count > 0 {
+		tx.Rollback()
 		return database.User{}, ErrDuplicateEmail
 	}
 

diff --git a/pkg/server/cmd/start.go b/pkg/server/cmd/start.go
@@ -22,10 +22,12 @@ import (
 	"fmt"
 	"net/http"
 	"os"
+	"time"
 
 	"github.com/dnote/dnote/pkg/server/buildinfo"
 	"github.com/dnote/dnote/pkg/server/config"
 	"github.com/dnote/dnote/pkg/server/controllers"
+	"github.com/dnote/dnote/pkg/server/database"
 	"github.com/dnote/dnote/pkg/server/log"
 	"github.com/pkg/errors"
 )
@@ -67,6 +69,12 @@ func startCmd(args []string) {
 		}
 	}()
 
+	// Start WAL checkpointing to prevent WAL file from growing unbounded.
+	database.StartWALCheckpointing(app.DB, 5*time.Minute)
+
+	// Start periodic VACUUM to reclaim space and defragment database.
+	database.StartPeriodicVacuum(app.DB, 24*time.Hour)
+
 	ctl := controllers.New(&app)
 	rc := controllers.RouteConfig{
 		WebRoutes:   controllers.NewWebRoutes(&app, ctl),

diff --git a/pkg/server/controllers/books.go b/pkg/server/controllers/books.go
@@ -203,11 +203,13 @@ func (b *Books) update(r *http.Request) (database.Book, error) {
 
 	var book database.Book
 	if err := tx.Where("user_id = ? AND uuid = ?", user.ID, uuid).First(&book).Error; err != nil {
+		tx.Rollback()
 		return database.Book{}, pkgErrors.Wrap(err, "finding book")
 	}
 
 	var params updateBookPayload
 	if err := parseRequestData(r, &params); err != nil {
+		tx.Rollback()
 		return database.Book{}, pkgErrors.Wrap(err, "decoding payload")
 	}
 
@@ -253,11 +255,13 @@ func (b *Books) del(r *http.Request) (database.Book, error) {
 
 	var book database.Book
 	if err := tx.Where("user_id = ? AND uuid = ?", user.ID, uuid).First(&book).Error; err != nil {
+		tx.Rollback()
 		return database.Book{}, pkgErrors.Wrap(err, "finding a book")
 	}
 
 	var notes []database.Note
 	if err := tx.Where("book_uuid = ? AND NOT deleted", uuid).Order("usn ASC").Find(&notes).Error; err != nil {
+		tx.Rollback()
 		return database.Book{}, pkgErrors.Wrap(err, "finding notes for the book")
 	}
 
@@ -270,6 +274,7 @@ func (b *Books) del(r *http.Request) (database.Book, error) {
 
 	book, err := b.app.DeleteBook(tx, *user, book)
 	if err != nil {
+		tx.Rollback()
 		return database.Book{}, pkgErrors.Wrap(err, "deleting the book")
 	}
 

diff --git a/pkg/server/database/database.go b/pkg/server/database/database.go
@@ -21,6 +21,7 @@ package database
 import (
 	"os"
 	"path/filepath"
+	"time"
 
 	"github.com/pkg/errors"
 	"gorm.io/driver/sqlite"
@@ -58,5 +59,67 @@ func Open(dbPath string) *gorm.DB {
 		panic(errors.Wrap(err, "opening database conection"))
 	}
 
+	// Get underlying *sql.DB to configure connection pool
+	sqlDB, err := db.DB()
+	if err != nil {
+		panic(errors.Wrap(err, "getting underlying database connection"))
+	}
+
+	// Configure connection pool for SQLite with WAL mode
+	sqlDB.SetMaxOpenConns(25)
+	sqlDB.SetMaxIdleConns(5)
+	sqlDB.SetConnMaxLifetime(0) // Doesn't expire.
+
+	// Apply performance PRAGMAs
+	pragmas := []string{
+		"PRAGMA journal_mode=WAL",   // Enable WAL mode for better concurrency
+		"PRAGMA synchronous=NORMAL", // Balance between safety and speed
+		"PRAGMA cache_size=-64000",  // 64MB cache (negative = KB)
+		"PRAGMA busy_timeout=5000",  // Wait up to 5s for locks
+		"PRAGMA foreign_keys=ON",    // Enforce foreign key constraints
+		"PRAGMA temp_store=MEMORY",  // Store temp tables in memory
+	}
+
+	for _, pragma := range pragmas {
+		if err := db.Exec(pragma).Error; err != nil {
+			panic(errors.Wrapf(err, "executing pragma: %s", pragma))
+		}
+	}
+
 	return db
 }
+
+// StartWALCheckpointing starts a background goroutine that periodically
+// checkpoints the WAL file to prevent it from growing unbounded
+func StartWALCheckpointing(db *gorm.DB, interval time.Duration) {
+	go func() {
+		ticker := time.NewTicker(interval)
+		defer ticker.Stop()
+
+		for range ticker.C {
+			// TRUNCATE mode removes the WAL file after checkpointing
+			if err := db.Exec("PRAGMA wal_checkpoint(TRUNCATE)").Error; err != nil {
+				// Log error but don't panic - this is a background maintenance task
+				// TODO: Use proper logging once available
+				_ = err
+			}
+		}
+	}()
+}
+
+// StartPeriodicVacuum runs full VACUUM on a schedule to reclaim space and defragment.
+// WARNING: VACUUM acquires an exclusive lock and blocks all database operations briefly.
+func StartPeriodicVacuum(db *gorm.DB, interval time.Duration) {
+	go func() {
+		ticker := time.NewTicker(interval)
+		defer ticker.Stop()
+
+		for range ticker.C {
+			if err := db.Exec("VACUUM").Error; err != nil {
+				// Log error but don't panic - this is a background maintenance task
+				// TODO: Use proper logging once available
+				_ = err
+			}
+		}
+	}()
+}