code: func (tx *protoTxn) Commit(ctx context.Context) error {
  	if tx.err != nil {
  		return tx.err
  	}
  	return tx.txn.Commit(ctx)
  }
docs: // Commit commits all operations in a transaction to the data store.
  // Commit is atomic - either all operations in the transaction are
  // committed to the data store, or none of them.