Goroutine too much

[wind-c]

Mochi MQTT creates 3 goroutines for one client，When there are hundreds of thousands or a million of connections, the impact on performance can be significant.
Should be optimized，Please refer to the https://speakerdeck.com/eranyanay/going-infinite-handling-1m-websockets-connections-in-go

[mochi-co]

Generally agree but this is likely not possible without a major refactor of the project. There are 3 go routines per client:

• Parent goroutine which sets up and holds the connection of the client itself.
• Reader goroutine which reads data from the connection.
• Writer goroutine which writes data from the connection.

In theory there are ways you could reduce the number of goroutines, but as I can think of, each comes with fairly severe penalties - such as slow clients blocking subsequent connections, or writing blocking reading.

I would say that hundreds of thousands of connections is currently outside the scope of this project - if you need that type of capacity I would be more comfortable recommending something like NATS or one of the many excellent enterprise MQTT solutions.

That said, always open to optimisation ideas!

[torntrousers]

Interesting. Has there been any profiling of Mochi MQTT to see how it its with lots of connections?

I looked through that mentioned slide deck (https://speakerdeck.com/eranyanay/going-infinite-handling-1m-websockets-connections-in-go) which on one slide about their example says "serving a million concurrent connections would consume over 20GB of RAM" - is that really a problem? If i needed to serve a million connections i'd expect to need to use a good sized machine, my laptop has 32GB of RAM, maybe it could serve a million clients with Mochi if I closed all my other running apps?

[perbu]

I don't see a problem with running a few hundred thousand goroutines, fwiw. They're not threads. Also, starting to optimize before we can measure the impact doesn't sound like a good idea. If we could see a significant performance degradation at some point then that would be a target to work against.