Memory leak with rooms

[Morthy]

We've been running into a memory leak problem in a production environment where socket.io receives a very large amount of new connections/disconnections in a relatively small amount of time.

It would appear that the automatic room that is created for a new socket is never deleted when the socket disconnected. We tested this by stripping out all of our logic and benchmarking against a simple socket.io instance, with no authentication logic, custom rooms, or even emitting any messages. Every 2 seconds we outputted the memory usage, connected sockets. and number of rooms:

Memory used: 14444584 - Connected sockets: 41 - Rooms: 56
Memory used: 15919872 - Connected sockets: 133 - Rooms: 159
Memory used: 23399352 - Connected sockets: 225 - Rooms: 251
Memory used: 31132280 - Connected sockets: 315 - Rooms: 344
Memory used: 34205984 - Connected sockets: 395 - Rooms: 436
Memory used: 29165872 - Connected sockets: 472 - Rooms: 527
Memory used: 29414112 - Connected sockets: 539 - Rooms: 620
Memory used: 38353000 - Connected sockets: 210 - Rooms: 652
Memory used: 41053952 - Connected sockets: 1 - Rooms: 652
Memory used: 41071808 - Connected sockets: 1 - Rooms: 652

We determined the number of rooms using:

Object.keys(io.sockets.adapter.rooms).length;

To confirm this, we created a memory dump before and after the connections and compared them using Chrome's dev tools. As you can see, there are many rooms remaining, even though no connections remained: http://i.imgur.com/wuftdnH.png

[Morthy]

Here's the bare bones server code used for testing:

var http = require('http'),
    io = require('socket.io');

var app = http.createServer();
var server = io(app);
app.listen(80);
var connections = 0;

server.on('connection', function(socket) {
    connections++;

    socket.on('disconnect', function() {
        connections--;
    });
});

setInterval(function() {
    var rooms = Object.keys(server.sockets.adapter.rooms).length;
    console.log('Connections: ' + connections + ' - Rooms: ' + rooms);
}, 2000);

[Marreck]

This bug should be fixed in the master. (see rase-@624e7cb ).

edit: After looking at https://github.com/Automattic/socket.io-adapter/blob/fc5930c5d11a59f7622145fedfdf495f65886cd5/index.js I think the room continues to exist, even though it is empty.

Adapter.prototype.del and Adapter.prototype.delAll should delete a room if they are empty.

[yads]

Looks like there was a pull request to fix this issue, but it was never accepted

socketio/socket.io-adapter#2

[yads]

So we ran a simple test with socket.io where we connect then disconnect. We ran the test using the existing code base and some code to delete a room once it becomes empty. Both versions of the code showed similar memory usage profiles. I.e. both started using memory, but then would drop down once the GC kicked in. Likely this "feature" of leaving rooms open is not what's causing the memory leaks you're seeing.