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by tomaytotomato9 hours ago |
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upvoteby Hendrikto8 hours ago|
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> As a Java dev, I have maybe used about 10-15 of them in my career.

So do we really need multiple thousand? Having all of them also makes finding the few you actually need much more difficult.

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upvoteby nradov6 minutes ago|
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Did you RTFM? It's not difficult to find the few you actually need.
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upvoteby KronisLV4 hours ago|
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> So do we really need multiple thousand?

Assuming that you don't need 99.9% of them (they should have sane defaults that you never have to change or even learn that they exist or what they are) until that super rare case when one will save your hide, I'd lean towards yes.

In other words, they might as well be an escape hatch of sorts, that goes untouched most of the time, but is there for a reason.

> Having all of them also makes finding the few you actually need much more difficult.

This is a good point! I'd expect the most commonly changed ones (e.g. memory allocation and thread pools) to be decently well documented, on the web and in LLM training data sets. Reading the raw docs will read like noise, however.

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upvoteby nkzd9 hours ago|
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Which JVM options do you use the most?
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upvoteby cogman109 hours ago|
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Heap size, GC algorithm.

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

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upvoteby marginalia_nu8 hours ago|
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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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upvoteby cyberpunk5 hours ago|
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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.
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upvoteby dpratt3 hours ago|
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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.
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