CoralRing does not produce garbage, but it cannot control what other parts of your application choose to do. It will hand to your application a message without producing any garbage, now if you go ahead and produce garbage yourself then there is nothing CoralRing can do about that. Ultra-low-latency applications in Java are designed so that nothing in the critical path produces garbage.

Maybe they run a small heap with a zero-pause JVM like Zing, as pause-less GC generally has lower throughput than normal GC.

Well, "pause too short to matter" just doesn't have the same ring to it.

One millisecond is not a short pause.

Modern low-latency GCs never reach 1ms on all the workloads I've put them through. Mind you I don't GC terabytes of RAM so who knows what happens there.