Now you're presumably thinking, "What a stupid question?". Surely, there's no one answer to this. It depends on several factors; what you're doing, where the code is running, and how many you need. However, I had never really thought about it in-depth before until someone asked me: "What is your favourite number of threads?". In this short (and hopefully fun) talk, I will take you through nearly all possible answers to this question and why they are both right and wrong on a technical and human level. Finally, I will give what I believe is the ultimate and final answer to the question: "What is the best number of threads?". There is no barrier to entry here. If you know what a thread is, then you're qualified enough to come along and have fun.

Jfokus

A conference talk transcript exploring the question of the optimal number of threads in Java applications. Covers CPU-bound vs IO-bound thread pool sizing formulas, benchmarking results on an 8-core system, Java 21 virtual threads and their limitations, Kubernetes millicores, and the ultra-low-latency single-threaded approach used at financial exchanges like LMAX. Concludes with a pragmatic argument that multi-threaded code is hard to read, test, debug, and maintain, so developers should minimize complexity where possible.

What's your favourite number of threads? By Ryan Healey