2014/06/28 16:39:23 [error] 9162#0: *1 FastCGI sent in stderr: "PHP message: PHP Fatal error:  Class 'Mongo' not found in /usr/share/nginx/html/req.php on line 4" whil$

and this code on req.php

<?php 
session_start();
//mongo connection
$connection = new Mongo();
//database name create if not exist
$keydb = $connection->selectDB('keydb');
$valdb = $connection->selectDB('valdb');
//collection name create if not exist
$keywords = $connection->keydb->kunci;
$konten = $connection->valdb->konten;
?>