It's not either/or. Everything needs to be tuned to achieve the final latency requirements. This includes tuning java code to eliminate creating "garbage", immu

It's not either/or. Everything needs to be tuned to achieve the final latency requirements. This includes tuning java code to eliminate creating "garbage", immutable string objects mostly, unnecessary object creation, creating short lived objects compared to long lived etc. The other part right sizing jvm generational partitions, using right gc algo etc. Next part would be to find out the code path with lowest latency requirement and making it hot/jitting. Even next part would be to tune OS for things like thread pinning etc etc. You can go further and tune the network layer. Every little thing counts. You can go even further and employ what's called mechanical sympathy (https://mechanical-sympathy.blogspot.com/ https://mechanical-sympathy.blogspot.com/) and write your code in a way that makes it easier for the processor to process faster. I've never worked with application that use off-heap allocations or no-gc requirements.