I've developed a web-based application in which a signed in user should send a message to the server telling he is still online every 3 seconds. The message is then processed by the server and a stored procedure is called in Mysql to set the user's status to online.
I've looked in to similar issues in which Comet and Ajax are compared (here or here) but considering that 3 second delay is acceptable and maximum users of 1000 are online in the system, is using Ajax a wise choice or Comet should be used?
For this kind of feature comet is more appropriate:
Your clients send messages (i'm online)
Your server broadcast the processed message (user X is still online)
In an ajax way you are only serving messages to server.
In order to get the "broadcast effect" in an ajax way. You will end up doing something similar to comet but with less efficient bandwidth.
Ajax:
Client send server - i'm in
Server process
Server send back to client list of user in.
In this case every client ask every 3 second the database for the COMPLETE "in" list.
In comet:
Client X send server - i'm in
Server process
Server send back to client S that user X is still online
In this case every client tell the server every 3 second that he is in.
The server send back to every connected client ONLY that x is still in
Comet is just the technique to broadcast back and push messages to client
Ajax is the technique to push client information to the server without having to refresh all the page.
Quoting wikipedia:
http://en.wikipedia.org/wiki/Comet_%28programming%29
Comet is known by several other names, including Ajax Push, Reverse Ajax , Two-way-web, HTTP Streaming,and HTTP server push among others.
So go comet :)
If you do not broadcast anything, then simple Ajax is the best option
In this particular case, since you do not need to send any information from the server to the client(s), I believe Ajax is the more appropriate solution. Every three seconds, the client tells the server it is connected, the database is updated, and you're done.
It could certainly be done using Comet, in which case you would basically ping each registered client to see if it is still connected. But, you would still need to run a query on the database for each client that responds, plus you would still need the client to notify the server on its initial connection. So, it seems to me that Comet would be more trouble than it's worth. The only thing that might make sense is if you could ping each registered client and store the responses in memory, then once all clients have been pinged you can run one single query to update all of their statuses. This would give you the added bonus of knowing as soon as a client disconnects as opposed to waiting for a timeout. Unfortunately, that is beyond the scope of my expertise with Comet so, at this point, I can't help to actually implement it.
Related
I’m bulilding a web app that requires communication between clients. For this I’m using socket.io. Some data however has to be updated regularly in the database.
Some of them not that often (preferences, on button click) others in every second for example a timer value. This can not be calculated because the timer can be paused.
Right now whenever a client emits an event, it also makes a request to the backend to updated the database. I was wondering if it would be a good idea to have the socket.io server update the database so the clients would only have to take care of the socket communication? It seems to me that having the browser do a request to the backend is a bit resource heavy and takes out a bit from the advantages of the socket based communication
Edit: the back end of the app and the socket server are two different servers but physically they are on the same machine so their communication could be faster
the main point of using socket.io is that it allows you to push data to clients and clients do not need to check your server constantly to get the last changes, and providing a low-overhead communication channel between the server and the client.
you can call an API and also emit data and many other things on user click in your application.
it is a good idea to have the socket.io server update the database and you can also authorize each socket, save client sockets information and ...
I have a Client that tell my server to contact another server and save the data there upon saving if successful I can receive a callback, how can I then tell the Client to refresh the page because this 2nd Server is also sending data to the Client, can I do it using headers?
There is no tranditional ways to push messages (refresh request and so on) to the webpage directly from the server.
Before giving some solutions, I'm sorry to say that your description to your question is quite ambiguous. server, another server, this 2nd Server is also sending data to the Client does not make much sense. You may reorganize your description to show the whole business logic better. Giving necessary code will be better.
So focusing on sending message from server to client within browser environment, there are several ways you could consider:
Ajax
You could use ajax to request the server at client side. You can poll the server at regular intervals, checking the response to determine whether the page should be refreshed.
Pro: widely supported, easy for both client side and server side
Con: polling is not a real-time solution and will make some redundant requests
Websocket
Pro: real-time bidirectional socket-like communication
Con: may be too heavy for the simple task you mentioned
Server push
Part of PWA specification
Pro: allow direct communication from server to client
Con: complexity, insufficient browser support
I've been searching online for days now and I can't find anyone who has this same problem with the VB6 Winsock. So here's my problem, I have a server with two winsocks in an array. I then have two clients each with one winsock control. Now the I have it set up is that the server first sends data to client A. Then client A receives that data and sends its own data back to the server. Then the server sends data to client B, once client B receives the data, it sends its own data back to the server. So data is being sent from a client to the server, then from the server to another client, then back to the server, and then on to another client. I did it this way because when I tried doing it the way I really want it to work, I was having problems. So I had to set it up this way in order to ensure that only one client is sending data to the server at any one time. This process works perfectly, however I want it to work in a different way, since as you can image, the more clients there are, the longer the delay in data transfer between each client and the server.
So what I really want to do, which I can't get to work, is have the clients send and receive data to the server whenever they want. That is, client A sends data to the server, and then the server sends data back, all while client B is doing the same thing. When I do this, even though I have a winsock array on the server, I run into a problem. When client A first connects, it begins sending and receiving data to the server. But once client B connects to the server, all communication between client A and the server stops, and only client B sends and receives data to the server. Now I've done some tests and client A remains connected to the server the whole time. But for some reason, it seems that if two clients send data to the server simultaneously, only one data arrival event fires, even though each winsock is on a different port. I have not installed VB6 SP6 yet, as I'm not sure this will fix the problem.
So I really do hope someone will read this and explain to me what it is that I'm not understanding or what it is that I'm doing wrong.
If you search for Microsoft KB articles on the Winsock control you will find a long history of flaws and bug fixes. There is absolutely no reason not to install SP6 before even attempting to use VB6, since a vast number of issues were resolved over time.
Once you've done that (and only then) is it really worth talking about problems of the sort you describe. At least it eliminates a significant number of known problems, and then it might be worth discussing your code.
Are you using none blocking sockets? I guess you should.
You should probably create a thread for each incoming connection.
So the main loop should act none blocking and create a thread for each incoming connection, that receives the data and sends the answer.
I have an intranet based CRM application developed in CodeIgniter 2.1 where the application is running on a local Apache server and around 20 clients are accessing it over LAN. This is to be connected to a call center setup where the call center application (running on a separate server) will do a HTTP post with caller's number as well as terminal number of the agent where the call is arriving to a URL of my Codeigniter application. I am using this data to populate a database table of call records.
Now from the terminal number (each terminal has static IP, and a session in Codeigniter is linked to IP as well) I can find out which user (login session) of my application is about to receive the call. I want to find a way out how I can send data from server side (it will be regarding the call like the number who is calling, past call records etc.) to that specific user's browser via AJAX or something similar? The agent's browser needs to display this information sent from server.
Periodic polling from browser by jquery etc. is not possible as the data needs to be updated almost instantaneously and rapid polling up to this extent will lead to high CPU usage at client end as well as extra load on network.
P.S.: I only want to know how to modify the browser data from server end.
In AJAX, asynchronous request/response doesn't involve polling; there's just an open TCP connection and non-blocking I/O. The client makes a request but returns immediately; when the server sends the response, the client is notified. So you can achieve what you want with AJAX's XMLHttpRequest without polling[1]. All you need is a url from which to serve your notifications. You could have one request thread and a general dispatch method, or different urls and different threads for each, depending on how you needed to scale.
[1] Well, to be honest, with very little polling. You'd really need to establish what the session/global timeout was and reissue requests within that time limit.
Is this chat using "long polling" or "http streaming" ?
http://go-mono.com/moonlight/chat.aspx
It's not anything that simple. It uses http://www.mibbit.com/chat, which is a full IRC client written in Javascript and Java. Blog at http://blog.mibbit.com/.
Edit: Here's your answer.
The first part I got working was the communications between browser and server. That’s done using 2 XMLHttpRequests. The first one is simply to send data from browser to server. It utilizes keep-alive, to minimise new connections.
The second XHR is the ‘receive lazy polling’ one. It connects to the server, and the server holds it open until there are messages available, or a timeout expires. This one is also keep-alive, so the next request goes down the same connection.
What you end up with is 2 connections held open to the server, with packets (json in this case), and some http headers from time to time.
To make sure the server would scale, I wrote a custom webserver in java using nio. It handles all of the connections in a single thread and as I say, scales to tens of thousands of connections.
If the client requests a new connection, it sends a request to the webserver, which then connects out, and starts proxying etc. It also runs an ident server in the case of irc connections so that an irc server can identify individual browsers. I looked at existing frameworks etc to do this sort of thing, but I valued learning how it all works, and thought that my use case may be specific enough to be able to optimise more than general frameworks can.