Batch inserts through Maxscale with C/J stall

public class BatchInsert {

    static final String ADDRESS = "127.0.0.1";

    static final String PORT = "4006";

    static final String USER = "maxuser";

    static final String PASSWORD = "maxpwd";

    static final String DB = "test";

    public static void main(String[] args) {

        try (Connection connection = DriverManager.getConnection("jdbc:mariadb://"

                + ADDRESS + ":" + PORT + "/" + DB + "?user=" + USER + "&password="

                + PASSWORD + "&useBatchMultiSendNumber=500")) {

            Statement stmt = connection.createStatement();

            stmt.execute("DROP TABLE IF EXISTS tt");

            stmt.execute("CREATE TABLE tt (d int)ENGINE=BLACKHOLE");

            for (int i = 0; i < 300; i++) {

                stmt.addBatch("INSERT INTO tt(d) VALUES (1)");

                if (i % 3 == 0) {

                    stmt.addBatch("SET @test2='aaa'");

                }

            }

            stmt.executeBatch();

            System.out.println("finished");

        } catch (Exception e) {

            System.out.println("Error: " + e.getMessage());

        }

    }

}