code: func (ssa *SQLStorageAuthority) SetOrderProcessing(ctx context.Context, req *corepb.Order) error {
  	tx, err := ssa.dbMap.Begin()
  	if err != nil {
  		return err
  	}
  	txWithCtx := tx.WithContext(ctx)
  
  	result, err := txWithCtx.Exec(`
  		UPDATE orders
  		SET beganProcessing = ?
  		WHERE id = ?
  		AND beganProcessing = ?`,
  		true,
  		*req.Id,
  		false)
  	if err != nil {
  		err = berrors.InternalServerError("error updating order to beganProcessing status")
  		return Rollback(tx, err)
  	}
  
  	n, err := result.RowsAffected()
  	if err != nil || n == 0 {
  		err = berrors.InternalServerError("no order updated to beganProcessing status")
  		return Rollback(tx, err)
  	}
  
  	return tx.Commit()
  }
docs: // SetOrderProcessing updates a provided *corepb.Order in pending status to be
  // in processing status by updating the `beganProcessing` field of the
  // corresponding Order table row in the DB.