How many concurrent connections can socket.io handle?

[Ponko]

Hi there.

I am preparing a small node.js app that will tell me how many users
are on my website at the moment. I will use socket.io:

var socket = io.listen(app);
socket.on('connection', function(client){
++userCount;
client.on('message', function(data){ });
client.on('disconnect', function(){
--userCount;
});
});

What if I have a website with LOADS of traffic. Will socket.io and
node.js handle so many concurent connections (i.e 1.000.000 at the
same time)? I am curious if socket.io will bring my node.js server
down...

[Arnout Kazemier]

No it will not handle 1M connections as it runs on a single process which are limited to about 1.7gb RSS in heap size, so you would need to scale across multiple process if you want to handle that.
Node will most like crash out of memory if you receive that much load without a scalable solution.

( I calculated the theoretical node.js real time limits: http://blog.3rd-eden.com/post/5809079469/theoretical-node-js-real-time-performance )