Too many subscriptions to socket.io in JavaScript

Question

I am using streaming provided by a vendor using socket.io using the following code:

var socket = io.connect('https://streamer.vendor-company.com/');
var subscription = ['sub1', 'sub2', 'sub3', 'sub4'];
socket.emit('SubAdd', { subs: subscription });
socket.on("m", function(message) {
    console.log(message);
    var messageType = message.substring(0, message.indexOf("~"));
    if (messageType == someMessageType) {
        dataUnpack(message);
    }
    else if (messageType == otherMessageType) {
        anotherDataUnpack(message);
    }
});  

The method dataUnpack and anotherDataUnpack perform some processing on the received message and display to the webpage. Now here, the array subscription may have around 45 subscriptions.

I want to know the affect on performance on my website. Does socket.io have some way for not flooding the client or are there any serious performance consideration? Is socket.io designed for such usage?

Updates

This is different from: Too many on-connection events with Socket.io, does it hurt? as mine is for Javascript/jquery and the question to which I gave link is for node.js.

The server is not under my control. Looking at jfriend00's answer, It seems that if I have 50 subscriptions and I get around 20-30 messages per sec, I need to handle this on client side. If so, what is the amount of incoming messages I should worry at? And if possible, any technique/strategy for handling high rate of incoming messages?

Answer 1

Does socket.io have some way for not flooding the client

No. If your server sends a message to the client, socket.io delivers it. It's all up to your server how many messages it sends and socket.io's job is to deliver every one of them you tell it to send.

or are there any serious performance consideration?

If you send a ton of messages to a ton of clients, that will potentially take a lot of processing and bandwidth. socket.io is just a messaging layer on top of webSocket which is a layer on top of TCP. So, if you send a socket.io message from server to a client or from server to all clients, it's one of more TCP packets being sent to the client(s). The only way to not flood the client is for your server to not send it more than it wants or can handle.

Is socket.io designed for such usage?

Socket.io is designed to reliably deliver messages from server to client or client to server. It just does what you tell it. If you tell it to deliver 1000 messages, that's what it will do.

If you have concerns about too many messages being sent to the client, then you need to modify your server to control that. For example, you might decide that a client should not be notified more than once every 5 seconds (for efficiency reasons). To implement that, you'd need an extra layer (of your own design) on the server. That is not something that socket.io has built-in features for.

---

If you're getting 20-30 messages per sec per subscription and each client has 50 subscriptions, that's 1000-1500 messages per second per client. That is indeed a lot and probably not sustainable at either the client side or the server side, especially on the server-side as you get lots of clients all doing the same thing. At 1000 messages per second, you have to process a message in under 1ms in order to keep from falling behind.

There are no special techniques for handling a high rate of incoming messages other than be extremely careful to limit what you do when each message arrives. For example, you would not want to be touching the browser DOM on each message. Perhaps you would queue them and modify the DOM in batch only once per second. Further advice would need to see what you're trying to do with these messages.

The better path would be to find a way to limit the number of messages being sent to each client, either by being smarter about what you subscribe to, finding ways to configure the subscription to not send you so much or creating an intervening server of your own that can be smarter about what is sent to each client.