Fix various migration issues (#5723)

* Indicate while backing up database
* Close migrate connection to db before optimising
* Don't vacuum post-migration

In most cases is probably not needed and can be an optonal user-initiated step

* Ensure connection close on NewMigrator error
* Perform post-migration using migrator connection

Flush WAL file at end of migration

pkg/sqlite/migrate.go

@@ -39,6 +39,12 @@ func NewMigrator(db *Database) (*Migrator, error) {
 	m.conn.SetConnMaxIdleTime(dbConnTimeout)
 
 	m.m, err = m.getMigrate()
+
+	// if error encountered, close the connection
+	if err != nil {
+		m.Close()
+	}
+
 	return m, err
 }
 
@@ -124,6 +130,27 @@ func (m *Migrator) runCustomMigration(ctx context.Context, fn customMigrationFun
 	return nil
 }
 
+func (m *Migrator) PostMigrate(ctx context.Context) error {
+	// optimise the database
+	var err error
+	logger.Info("Running database analyze")
+
+	// don't use Optimize/vacuum as this adds a significant amount of time
+	// to the migration
+	err = analyze(ctx, m.conn)
+
+	if err == nil {
+		logger.Debug("Flushing WAL")
+		err = flushWAL(ctx, m.conn)
+	}
+
+	if err != nil {
+		return fmt.Errorf("error optimising database: %s", err)
+	}
+
+	return nil
+}
+
 func (db *Database) getDatabaseSchemaVersion() (uint, error) {
 	m, err := NewMigrator(db)
 	if err != nil {