presto-accumulo/src/main/java/io/prestosql/plugin/accumulo/AccumuloConnector.java/AccumuloConnector/beginTransaction
class AccumuloConnector:    @Override
    public ConnectorTransactionHandle beginTransaction(IsolationLevel isolationLevel, boolean readOnly)
    {
        checkConnectorSupports(READ_UNCOMMITTED, isolationLevel);
        ConnectorTransactionHandle transaction = new AccumuloTransactionHandle();
        transactions.put(transaction, metadataFactory.create());
        return transaction;
    }