Simple php chat

I am working on a quick and easy jQuery / PHP chat to host visitors for communication on my site. I launched peaks from 200 simultaneous users of the website (connected users), in which no more than 10-20 people actually communicated.

Here quirk:

As I already experienced twice (I thought it was more likely an unlikely event than something that happens after you perform something specific) In the chat, several messages are loaded that are already red and display them.

Trying to leave the chat system as simple as possible, I came up with this code:

HTML code:

<div class="chat">

    <ul class="chat">

        <li class="chat" >

            <h5 class="chat">Date</h5>
            <h6 class="chat">Time</h6>
            <h4 class="chat">User</h4>
            <br/>
            <q class="chat">Message</q>

        </li>

    </ul>

    <input class="chat" placeholder="write something..."/>

</div>

, - li jQuery li preend ul.

jQuery CODE:

:

$(document).ready(function(){

    chatSnippet = $('ul.chat').html(); // here chatSnippet is a global variable
    $('ul.chat').html('');

    $('input.chat').change(function(event){// Send your message

    message = $(this).attr('value');

// first thing I perform an asynchronous POST to the receiving PHP 

    $.post(

        'php/chatRec.php',

        {

            user : currentUser,
            message: message,

        }

    );

// meanwhile I add a new li element to the chat html with the content just submitted


    date.setTime(event.timeStamp);

    hours = ''+date.getHours();

    if(hours.length < 2) hours = '0'+hours;

    minutes = ''+date.getMinutes();

    if(minutes.length < 2) minutes = '0'+minutes;

    day = ''+date.getDate();

    if(day.length < 2) day = '0'+day;

    newChatMessage = chatSnippet.replace('Date', ''+day+' '+months[date.getMonth()]);
    // here months is an array with the months names (in italian)
    newChatMessage = newChatMessage.replace('Time', ''+hours+':'+minutes);

    newChatMessage = newChatMessage.replace('User', connectedUser);

    newChatMessage = newChatMessage.replace('Message', message);

    $mess = $(newChatMessage);

    $mess.hide().prependTo('ul.chat').fadeIn(500);

    $(this).attr('value','');

});

refreshChat(''); // this function retrives new messages from the DB

// Here I perform a void refreshChat call so I'll get all the messages in the DB regardless from the currentUser (at page refresh)

});

:

// This code is placed outside (before) the .ready function

function refreshChat(user){// Receiving messages

$.post(

    'php/chatInv.php',

    {

        user : user,
        token: lastMessage // this variable contains the token of the last red message

    },

    function(data){

        receivedMessages = jQuery.parseJSON(data);

        for(message in receivedMessages){

            message = receivedMessages[message].Message;

            date = receivedMessages[message].Day.split('-');
            time = receivedMessages[message].Time.split(':');

            newChatMessage = chatSnippet.replace('Date', ''+date[2]+' '+months[parseInt(date[1])-1]);

            newChatMessage = newChatMessage.replace('Time', ''+time[0]+':'+time[1]);

            newChatMessage = newChatMessage.replace('User', receivedMessages[message].Sender);

            newChatMessage = newChatMessage.replace('Message', message);

            $mess = $(newChatMessage);

            $mess.hide().prependTo('ul.chat').fadeIn(500);

            lastMessage = receivedMessages[messages].token;

        }

        nextRefresh = setTimeout("refreshChat('"+currentUser+"')",2000);

// When I'm done I set a timeout of 2 secs and then perform another refresh

    }

);

}

PHP CODE:

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    mysql_connect("localhost", "root", "root") or die(mysql_error());
    mysql_select_db("chat") or die(mysql_error());

    $characters = array('0','1','2','3','4','5','6','7','8','9','a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z','A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z');

    $token = $characters[rand(0,61)].$characters[rand(0,61)].$characters[rand(0,61)].$characters[rand(0,61)].$characters[rand(0,61)];

    $all_Msgs = mysql_query("SELECT * FROM Messages ORDER BY ID");

    $prev_Msg = array('ID' => 1 , 'Sender' => $_POST['user'], 'Message' => $_POST['message'], 'Day' => date("Y-m-d"), 'Time' => date("H:i:s"), 'token' => $token);

    while($Msg = mysql_fetch_array($all_Msgs)){

        $update_success = mysql_query("UPDATE Messages SET Sender='".$prev_Msg['Sender']."', Message='".$prev_Msg['Message']."', Day='".$prev_Msg['Day']."', Time='".$prev_Msg['Time']."', token = '".$prev_Msg['token']."' WHERE ID=".$Msg['ID']);

        $prev_Msg = $Msg;

    }

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:

    mysql_connect("localhost", "root", "root") or die(mysql_error());
    mysql_select_db("chat") or die(mysql_error());

    $receiver = $_POST['user'];
    $token = $_POST['token'];

    $all_Msgs = mysql_query("SELECT * FROM Messages ORDER BY ID");

    $newMessages = array();

    while($Msg = mysql_fetch_array($all_Msgs)){

        if($Msg['token'] == $token) break;

        if($Msg['Sender'] != $receiver) array_unshift($newMessages,$Msg);

    }

    echo json_encode($newMessages);

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: 10-20 ?