func (wb *WriteBatch) Flush() error {
	wb.Lock()
	_ = wb.commit()
	wb.txn.Discard()
	wb.Unlock()

	wb.wg.Wait()
	// Safe to access error without any synchronization here.
	return wb.err
}
func (wb *WriteBatch) Flush() error {
	wb.Lock()
	_ = wb.commit()
	wb.txn.Discard()
	wb.Unlock()

	wb.wg.Wait()
	// Safe to access error without any synchronization here.
	return wb.err
}
// Flush must be called at the end to ensure that any pending writes get committed to Badger. Flush
// returns any error stored by WriteBatch.