Storing chat history in a single database table - php

Question

I am trying to create a simple AJAX/PHP chat application to enable communication between registered users on a website. The problem with it is storing the chat history. I thought of storing all the chat messages in a single database (with columns like user1, user2, message, time), and then at every AJAX request, search the database for a matching message between the users, but I think this might be extremely inefficient. Is it a good idea to implement it this way, and what are some good ways of handling this?

Answer 1

Since a chat room has to constantly get updates, I wanted to minimize the requests to a minimum, so I just labeled each message with the database id. Since every user can see all the messages for that room, the request is just sending the id to the server to see if there were any new posts. If there were, it returns the new posts and updates the page.
Here's the JavaScript that I use:
var csrf = $("input[name='csrf_test_name']").val();
load_messages();
load_users();
$("#submitbutton").click(function(){
var message = $("#content").val();
$.post(base_url + "index.php/chat/ajax_post", {
text: message,
csrf_test_name: csrf
});
$("#content").attr("value", "");
return false;
});
function load_messages(){
var last = $('#messagewindow p:last').attr('id');
$.ajax({
url: base_url + "index.php/chat/ajax_retrieve",
type: "POST",
data: {
last: last,
csrf_test_name: csrf
},
cache: false,
success: function(html){
if(html.substr(1, 1) == 'p'){
var oldscrollHeight = $("#messagewindow").prop("scrollHeight") - 20;
var id;
var tag;
var user;
var uid;
//remove messages that exceed the max - determined on the server side
$('#messagewindow p:lt(' + $(html).siblings().size() + ')').remove();
//add messages, emoticons and classes based on whether its the user or someone else
$(html).find('b').each(function(){
if ($(this).html() == user_name + ':'){
$('#messagewindow').append($(this).parent().emoticons(base_url + 'images/emoticons').attr('class', 'self'));
} else {
$('#messagewindow').append($(this).parent().emoticons(base_url + 'images/emoticons').attr('class', 'others'));
}
});
//scroll screen
var newscrollHeight = $("#messagewindow").prop("scrollHeight") - 20;
if(newscrollHeight > oldscrollHeight){
$("#messagewindow").animate({ scrollTop: newscrollHeight }, 'normal');
}
$(html).find('span').each(function(){
id = $(this).attr('id');
uid = 'u' + id.substr(1);
if (id.substr(0, 1) == 'e' && $('#userwindow p[id="' + uid + '"]').size() < 1){
user = $(this).prev().html();
tag = "<p id='" + uid + "'>" + user.substr(0, user.length - 1) + "</p>";
$('#userwindow').append(tag);
} else if(id.substr(0, 1) == 'x') {
$('#userwindow p[id="u' + id.substr(1) + '"]').remove();
}
});
}
}
});
}
function load_users(){
$.ajax({
url: base_url + "index.php/chat/ajax_users",
cache: false,
success: function(html){
if(html.substr(1, 1) == 'p'){
$("#userwindow").html(html);
}
}
});
}
setInterval(load_messages, 2000);
setInterval(load_users, 240000);

Answer 2

What would be wrong with your method?
Use the proper MySQL indexes on your table (I would say on the two columns user1, user2 and on timestamp or unique ID for the order) and the performance will be good enough.
You can add the curent timestamp to the AJAX request to retreive only message that you didn't loaded the call before.