Memory Leak in Express.js with EventSource

Question

I think I am running into a memory leak with an Express app when connecting x number of EventSource clients to it. After connecting the clients and sending them x messages and disconnecting them, my Express app only releases a small amount of the allocated Heap/RSS.

To confirm this I saved a Heapdump when starting the server and one after connecting 7,000 clients to it and sending x messages to each client. I waited for a while to give the GC a chance to clean up before taking the heap snapshot.

To compare these heap snapshots I loaded them in the Chrome Developer Tools Profile view and chose the "Comparison" mode.

My questions are:

1) How to interpret these numbers? (For reference see the attached heap snapshot screenshot.)

2) For instance it looks like that the Socket objects doesn't almost free any objects at all, is that correct?

3) Can you give me more tips to investigate the problem?

Answer 1

You could be free from memory leak and as a bonus avoid the garbage collector. All you got to do is object polling.

You could do something like

var clientsPool = new Array(1000);
var clientsConnected = [];

When a new client connects, you do

var newClient = clientsPool.pop();
//set your props here
clientsConnected.push(newClient);

That's an awesome way to avoid the Garbage Collector and prevent memory leak. Sure, there's a little more work to it and you will have to manage that carefully but it's totally worth for performance.

There's an awesome talk about it, here you go https://www.youtube.com/watch?v=RWmzxyMf2cE