Are we done here? We thought so at first. So the JVM is now aware of cgroup memory limits – you just need to enable that feature. Note that -XX:+UseCGroupMemoryLimitForHeap requires -XX:+UnlockExperimentalVMOptions in order to work. Exactly the same as in the non-docker examples. Uintx DefaultMaxRAMFraction = 4 Īnd that’s it. $ java -XX:+PrintFlagsFinal -version | grep -Ei "maxheapsize|maxram" On my brand new MacBook Pro 2018 this yields the following heap size: Per default the JVM automatically configures heap size according to the spec of the machine it is running on. We stitched this article together during a few Fridays at the office at adorsys. We also like to argue work together and this article is the result of one particularly interesting discussion about the JVM setting +UseCGroupMemoryLimit. Joe has a very strong operations background and I feel more at home with software development - yet we often do similar stuff. Joe and I both do a lot of work with Java on OpenShift/Kubernetes. We’re keeping it online as a reference but please see our follow-up article +UseContainerSupport to the Rescue for more details. UPDATE: Things Have Changed for Java 8u191+ and 10/11/12+Ī lot has changed since Java 8u191 and things should work out of the box. Java 10+ brings a lot of improvements but still needs manual configuration. XX:MaxRAMFraction=1 is especially dangerous. Otherwise you risk wasting resources and money or getting your containers killed at the worst time possible. You need to know what -XX:+UseCGroupMemoryLimitForHeap does and you need to fine tune some parameters for every deployment. Although the JVM can read cgroup memory limits and adapt memory usage accordingly since Java 9/8u131, it’s not a golden bullet. Java memory management and configuration is still complex. JVM Memory Settings in a Container Environment TL DR: The Bare Minimum You Should Know Before Going Live
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