presto-iceberg/src/main/java/io/prestosql/plugin/iceberg/IcebergConnector.java/IcebergConnector/beginTransaction
class IcebergConnector:    @Override
    public ConnectorTransactionHandle beginTransaction(IsolationLevel isolationLevel, boolean readOnly)
    {
        checkConnectorSupports(READ_COMMITTED, isolationLevel);
        ConnectorTransactionHandle transaction = new HiveTransactionHandle();
        try (ThreadContextClassLoader ignored = new ThreadContextClassLoader(getClass().getClassLoader())) {
            transactionManager.put(transaction, metadataFactory.create());
        }
        return transaction;
    }