PHP with Ajax slow response time - php

Question

I'm doing a program that would ask user to search from Mysql table based on onKeyup. But it seems that the response time is very slow while I don't have that much of data ~ 2873 records.
Here is my PHP code :
<?php
session_start();
if(isset($_SESSION['master'])){
require_once('connect_db.php');
require_once('output_fns.php');
<div id="openModal6" class="modalDialog6">
<div>
X
<h2><center>Search Item</center></h2>
<p>
<table>
<tr><td>
<b>Item No. :</b><br />
//User input and onKeyup
<input type="text" value="" id="item_s" autofocus required onKeyUp="related_item(document.getElementById('item_s').value,document.getElementById('store_s').value);">
<td><b>Stor</b><br />
//User select Store by default usually its first store
<select name='store_s' id='store_s'>
<?php
$query = "SELECT * from stores_list";
$result = mysql_query($query);
if(mysql_num_rows($result)>0){
$num = mysql_num_rows($result);
for($i=0;$i<$num;$i++){
$row = mysql_fetch_assoc($result);
echo "<option value='{$row['short']}'>{$row['short']}</option>";
}
echo "</select>";
}
else{
//No Stores Available
echo "No Stores Found !";
}
?>
</td>
</tr>
<tr><td align="center" colspan="3">
//Response Output Here
<div id="txtHint4">Waiting...</div>
</td></tr>
</table>
</p>
</div>
</div>
<?php
}
Of course this is a Modal dialogue so it basically opens up when user Click on |Search Button| and using Onclick=
As for Ajax get_item.php
<?php
require_once('connect_db.php');
$q=$_GET['q'];
$s=$_GET['s'];
if($_GET['q']=="---"){
return true;
exit();
}
//Select Result From table where item Like
$query="SELECT * FROM store_items WHERE item_no LIKE '".$q."%' AND store = '".$s."' ORDER by sub Asc";
$result = mysql_query($query);
if(mysql_num_rows($result)>0){
echo "<br />";
echo "<table width=100% height=% align=center border=1 bgcolor=white cellpadding=5 cellspacing=0 style='font-size:12px;'>";
echo "<tr><td align=center><b>Item Number</b><td align=center><b>QTY</b><td align=center><b>Unit Cost</b></td><td align=center><b>Unit Sell</b></td><td align=center><b>Cat</b></td><td align=center><b>Sub</b></td><td align=center><b>Description</b></td><td align=center><b>Store</b></td></tr>";
while($row = mysql_fetch_assoc($result)){
echo "<tr><td align=center>{$row['item_no']}</td><td align=center>{$row['qty']}<td align=center>{$row['actual_price']}</td><td align=center>{$row['selling_price']}</b></td><td align=center>{$row['cat']}</td><td align=center>{$row['sub']}</td><td align=center>{$row['short']}</td><td align=center>{$row['store']}</td></tr>";
//End of While loop
}
}
else{
echo "<br /><center><font color=red>Sorry Item Number Not Found !</font></center>";
}
?>
And finally the Function related_item
function related_item(str,str2)
{
if (str=="")
{
document.getElementById("txtHint4").innerHTML="";
return;
}
if (window.XMLHttpRequest)
{// code for IE7+, Firefox, Chrome, Opera, Safari
xmlhttp=new XMLHttpRequest();
}
else
{// code for IE6, IE5
xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
}
xmlhttp.onreadystatechange=function()
{
if (xmlhttp.readyState==4 && xmlhttp.status==200)
{
document.getElementById("txtHint4").innerHTML=xmlhttp.responseText;
}
}
xmlhttp.open("GET","get_item.php?q="+str+"&s="+str2,true);
xmlhttp.send();
}
What have I done wrong this far? it should fetch data quickly from the table, I don't understand like around 4-5 seconds waiting time to see data coming up inside <div id='txtHint4'>Response</div>
Please Note the items are only numbers , example (001200201000)
UPDATE :
I've checked chrome developer tool network to test out the delay part and it seems the delay goes on get_item.php file Here are the results
Query 0.36
Stalled 0.5
Request Sent 0.14ms
Waiting (TTFB) 77.555ms
Content Download 3.40s
So does it mean that there is something wrong with my PHP file? what other or better way to enhance the code? Its straight forward reading from table. Maybe I'm missing something here