code: func (db *ProtoWrapper) NewTxn() keyval.ProtoTxn {
  	return &protoTxn{txn: db.broker.NewTxn(), serializer: db.serializer}
  }
docs: // NewTxn creates a new Data Broker transaction. A transaction can
  // hold multiple operations that are all committed to the data
  // store together. After a transaction has been created, one or
  // more operations (put or delete) can be added to the transaction
  // before it is committed.