<?php
session_start();
if( isset($_SESSION['num']) )	$_SESSION['num']++;
else	$_SESSION['num'] = 1;
$num = $_SESSION['num'];
/*****************************/
$mysqli = new mysqli("localhost", "user", "pass", "test");
if (mysqli_connect_errno()) {
    printf("Connect failed: %s\n", mysqli_connect_error());
    exit();
}
$mysqli->autocommit( false );

$mysqli->query("INSERT INTO sometable VALUES ('test - $num')");


$mysqli->rollback();

$mysqli->close();
?>