使用mysql进行ajax长轮询

Im使用类似的脚本，如下所述：来自mysql的长轮询信息不起作用在我的网站上，它是有效的，但当我刷新页面或单击其他链接时，我会收到错误警报+网站开始严重滞后，有人能告诉我是什么原因造成的吗？

我的代码：

$oldIDq = mysql_query("SELECT * FROM messages ORDER BY id DESC LIMIT 1");
while($oldrow = mysql_fetch_array($oldIDq)){
$oldID = $oldrow['id'];    
}
$func = '
var oldID = '.$oldID.';
function wait() {
$.ajax({
    type: "GET",
    url: "../scripts/msg_scripts/msg.php?oldid=" + oldID,
    async: true,
    cache: false,
    success: function (data){
     var json = eval(''('' + data + '')'');  
     if (json[''msg_content''] != "") {
      alert("new meassage added");   
     } 
     oldID = json[''oldID''];
     setTimeout(''wait()'',1000);
    },
    error: function(XMLHttpRequest, textStatus, errorThrown){
      alert("error: " + textStatus + "(" + errorThrown + ")");  
      setTimeout(''wait()'',15000);
    }
});
}
$(document).ready(function(){
    wait();
});
';

服务器：

<?php 
    session_start();
    $connect = mysql_connect ("localhost", "root", "")
or die ("couldnt connect");
mysql_select_db ("***") or die ("not found"); //if db was   not found die
mysql_query("SET NAMES 'utf8'");
$oldID = $_GET['oldid']; 
$result = mysql_query("SELECT id FROM messages ORDER BY id DESC LIMIT 1");
while($row = mysql_fetch_array($result))
{
    $last_msg_id = $row['id']; 
}
while($last_msg_id <= $oldID)
{
    usleep(1000);
    clearstatcache();
    $result = mysql_query("SELECT id FROM messages ORDER BY id DESC LIMIT 1");
    while($row = mysql_fetch_array($result))
    {
        $last_msg_id = $row['id'];
    }
}
$response = array();
$response['msg'] = 'new';
$response['oldID'] = $last_msg_id;
echo json_encode($response);
?>