mqtt mosquitto linux connection limit

Question

How are users getting past a 1024 connection limit in Linux in association with doing MQTT for push notification?

I am using Mosquitto server, which I think I read does

Answer 1

In theory you could up the Linux setting for max number of sockets for mosquitto to what you need. The question then is around performance. The key metric is number of messages per second total. If you have 20k clients connected, how many will be active and how many messages will each be sending?

As an example, if half of your clients are active and sending 1 message per second, there are 10k msps - incoming only of course. If each of those messages is 10 bytes, you're at a sustained 100kB/s or 800kbps.

Another aspect is how your topic hierarchy is arranged. I can't tell you what is best, but it will certainly have an effect.

My best suggestion would be to write a client that simulates a real person, then use it to so real testing of your scenario.

I have seen examples of extreme client count: http://bit.ly/HytRpK but have no more details.

One final point: IBM are currently producing a redbook on MQTT. It should be available 'in spring', i.e. soon. I think it will cover scaling issues.