Is my code a performance killer? - php

Question

I am showing the value of the timer.php through AJAX in index.php . However I am concern about the performance of this, if it is a server killer if there are 30 people online, and things like this. Do you suggest me some edits?
Thank you.
index.php
<script language='JavaScript'>
setInterval( 'SANAjax();', 1000 );
$(function() {
SANAjax = function(){
$('#dataDisplay').load('timer.php');
}
});
</script>
<div id="dataDisplay"></div>
timer.php
function time_difference($endtime){
$days= (date("j",$endtime)-1);
$hours =date("G",$endtime);
$mins =date("i",$endtime);
$secs =date("s",$endtime);
$diff="'day': ".$days.",'hour': ".$hours.",'min': ".$mins.",'sec': ".$secs;
return $diff;
}
$future_time = mktime(0, 0, 0, 9, 19, 2011);
$now_time = strtotime("+2 hours");
$end_time = $future_time - $now_time;
$difference = time_difference($end_time);
if ($future_time <= $now_time ) { echo "Date reached"; } else { echo $difference; };
?>

Answer 1

Depends on your server specs and number of clients, this could quickly become a server-killer.
The multiple calls to a file every second will quickly put a lot of load for nothing though, so best practice calls for using a javascript timer countdown. I particularly like this one: http://stuntsnippets.com/javascript-countdown/
And for the jQuery implementation:
<script type="text/javascript">
var myDate = new Date(); //Retrieve actual date
myDate.setTime(this.getTime() + (3600 * 2)); //Add two hours
$(document).ready(function() {
$("#time").countdown({
date: myDate.toGMTString(),
onComplete: function( event ){
$(this).html("completed");
},
leadingZero: true
});
});
</script>
<p id="time" class="time"></p>
This should be enough, no more need for PHP calls and the client does everything.

Answer 2

By setting a setInterval for every second, you are basically saying that for 30 clients, you will be getting roughly 30 txn per second to your php server. Its hard to say its a performance killer outside of just saying you will have to handle 30tps for this simple call. I would first quesiton why you are doing this with a server side script. You could just as easily give the html file a datetime when the page loads and do the countdown with just javascript in the browser.

Answer 3

I use jQuery Countdown http://keith-wood.name/countdown.html to put a timer on my pages to let the user know when they are going to be logged out of the system due to inactivity.
You can bind a function to the counter expiring event.
http://code.google.com/p/jquery-countdown/ ...Simple example
http://keith-wood.name/countdown.html ...shows off all the bells and whistles...
It can be as simple as the first one or as detailed as the second!
-=Bryan