NodeJS & Socket.IO

Question

I am facing a strange issue while using NodeJS and Socket.io.

Server which receive data via ZeroMQ. That work perfect. For each message from ZeroMQ, I used sockets.volatile.emit to send that to all connected clients. The issue arise only for large number of connected accounts (more than 100), it seems there is a queue on the sending to clients (client receive message in delay that keep increasing)

Note : Each connected client received each message from ZeroMQ, so basically for more client there is more data sent over the socket.IO.

Via Logs/Debug i know the receive from ZeroMQ has no delay and all works on that part. The emitting seems to have a queue or delay that keeps increasing.

The messages rate is 80 messages/sec for each client.

Note: NodeJS 0.10.20 and Socket.IO 0.9.16.

How can I control that to prevent client received old messages ?

Answer 1

Checkout this article it will tell you a lot of the basic mistakes and it's, about blocking the event loop which seems pretty similar to what your doing.

Maybe use tools such as: Debug and Blocked i think it would help solve you'r issue. Both to debug where you creating a bottleneck on performance & other basic issues.

Alternatively hook your node project up on PM2 and bind it to Keymetrics.IO this will give you a good view into your server and why it's running slow and why you make a performance bottleneck.

Its hard to solve your problem without code examples but here is 3 reasons why your app or you could create bottlenecks (maybe unknowingly):

• Parsing a big json payload with the JSON.parse function.

• Trying to do syntax highlighting on a big file on the backend (with something like Ace or highlight.js).

• Parsing a big output in one go (such as the output of a git log command from a child process).

More info in the first article in section 2 called "Blocking the event loop"

A question related to yours, this one.

Wanna know more about the Event loop i can warmly direct you to a tread "How the single threaded non blocking IO model works in Node.js"

Here is a model of the Node.js Processing model, to see what happens on the event loop and its surroundings