Simple PHP script on loop causing server CPU overload - php

Question

I have an AJAX call on a loop, set to 1000 miliseconds.
The PHP script is simple, it just puts some information (a number) into a session variable. Yesterday I've recived an email from my hosting provider (HostGator), which states that I've been using 75%+ of CPU on shared hosting. After looking the logs, I've found that the problem is in that AJAX call. Here is the code:
PHP (ajax.session.php):
<?php
session_start();
$movieID_e = $_POST['id'];
$state = trim(strtolower($_POST['status']));
if ($state == 'playing') {
if (empty($_SESSION[$movieID_e])) {
$_SESSION[$movieID_e] = 1;
}
else {
$_SESSION[$movieID_e]++;
}
}
echo $_SESSION[$movieID_e];
?>
Javascript:
function interval(func,wait,times){
var interv = function(w, t){
return function(){
if(typeof t === "undefined" || t-- > 0){
setTimeout(interv, w);
try{
func.call(null);
}
catch(e){
t = 0;
throw e.toString();
}
}
};
}(wait,times);
setTimeout(interv, wait);
};
var watched = (function() {
var executed = false;
return function () {
$.post('ajax.session.php',{id:'<?php echo encrypt($id); ?>',status:'none'},function(result) {
if (result == 1000) {
if (!executed) {
executed = true;
var highlightad = introJs();
highlightad.setOptions({
steps: [
{
element: '#advertisment1',
intro: 'test',
position: 'bottom'
},
{
element: '#advertisment2',
intro: 'test2',
position: 'left'
}
]
});
highlightad.start();
}
}
else {
executed = false;
return false;
}
});
};
})();
interval(function(){watched()},1000,3000);
Explanation of JS:
function interval() -> Alternative to setInterval(), taken from thecodeship.com
function watched() -> AJAX request to file ajax.session.php shown above. If the result is 1000 then it highlights a part of a website using Intro.JS.
interval(function(){watched()},1000,3000); -> repeat watched() every 1000ms, max. number of repetitions is 3000 times.
Note that PHP script (ajax.session.php) is also called by AJAX from another script, also with function interval() every 1000ms.
I am using the interval() every second to count the number of seconds that past in a video player.
Do you have any suggestions on how to prevent CPU overload with the following script?

Answer 1

What server stats do you have? I think the problem is, that you have too much traffic for a weak server. Also of course 1second intervals for ajax calls are tooo often. Check your console, you will see that most of them will get timedout.
Sessions will be server side, so it will use servers resources. If you would convert your script to cookies, then the data will be stored in users browser. Also you could use $.cookie jQuery plugin to easily read the cookies via JS, so no need to ajax call.
Also, I would not recommend to use sessions at all, unless making some highly secure login system. I would recommend to use memcache to store temporary data.
Also, I'm pretty sure your JS could use optimization, because on first look I didn't see that you would check if one ajax call is active already. So it wouldn't ajax call before the last call was finished. Otherwise you can imagine the pointless ajax calls going to the server, where 50% of them get timedout.