Which JVM options do you use the most?

▲ cogman10 8 hours ago | parent [-]

Heap size, GC algorithm.

I suggest most people never touch almost any other options. (Flight recording and heap dumps being the exception).

▲ marginalia_nu 8 hours ago | parent [-]

GC threads are generally often useful on multi-tenant systems or machines with many cores, as Java will default-size its thread pools according to the number of logical cores. If the server has 16 or more cores, that's very rarely something you want, especially if you run multiple JVMs on the same host.

Not JVM options, but these are often also good to tune:

    -Djdk.virtualThreadScheduler.parallelism
    -Djdk.virtualThreadScheduler.maxPoolSize
    -Djava.util.concurrent.ForkJoinPool.common.parallelism

In my experience this often both saves memory and improves performance.

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cyberpunk 4 hours ago | parent [-]

You can get into difficulty with kubernetes here, as your jvm will detect all cores on the node but you may have set a resources limit on the pod/whatever, so it’ll assume it can spend more time doing stuff than it actually can, so often times it’s quite necessary to tune some things to prevent excessive switching etc.

	▲	dpratt 2 hours ago \| parent [-]
		Modern JVMs will detect orchestrator-set cgroup limits and size themselves accordingly. If you, for example, set a cpu limit for a pod to “1”, the JVM will size itself as if it was running on a single core machine.