code: func (b *FastLogStore) Close() error {
  	b.mu.Lock()
  	defer b.mu.Unlock()
  	if b.closed {
  		return ErrClosed
  	}
  	b.closed = true
  	if b.persist {
  		b.file.Sync()
  		b.file.Close()
  	}
  	return nil
  }
docs: // Close is used to gracefully close the DB connection.