presto-base-jdbc/src/main/java/io/prestosql/plugin/jdbc/BaseJdbcClient.java/BaseJdbcClient/getConnection
class BaseJdbcClient:    @Override
    public Connection getConnection(JdbcIdentity identity, JdbcSplit split)
            throws SQLException
    {
        Connection connection = connectionFactory.openConnection(identity);
        try {
            connection.setReadOnly(true);
        }
        catch (SQLException e) {
            connection.close();
            throw e;
        }
        return connection;
    }