code: func (db *DB) Close() error {
  	db.rwlock.Lock()
  	defer db.rwlock.Unlock()
  
  	db.metalock.Lock()
  	defer db.metalock.Unlock()
  
  	db.mmaplock.RLock()
  	defer db.mmaplock.RUnlock()
  
  	return db.close()
  }
docs: // Close releases all database resources.
  // All transactions must be closed before closing the database.