JVM release unused heap

I have a Springboot application with Mule running inside a docker container as a micro service. It takes about 700MB even when it is idle. It is noticed that JVM has allocated heap of 380 MB which is max heap provided using -Xmx parameter. Though max heap is allocated, the micro service only use about 50 MB when idle. The question is how to released unused memory back from JVM.

It seems that reducing MaxHeapFreeRatio we can ask JVM to shrink when there is more free memory ratio. However MinHeapFreeRatio=20 -XX:MaxHeapFreeRatio=40 did not make much difference and JVM did not release memory. But when I use -Xmn with above two parameters JVM releases heap memory as expected. See below image for example scenario.

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  • Java version 8

    -Xmn100M  -XX:+PrintGCDetails  -XX:MinHeapFreeRatio=20 -XX:MaxHeapFreeRatio=40 -Xmx384M

    enter image description here

    1. Why does MinHeapFreeRatio and MaxHeapFreeRatio does not work as expected?
    2. If above parameters are fine what are the consequences of -Xmn and what is the value of it should be?
    3. What are other solutions in order to achieve the task of releasing memory back from JVM?

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  • One Solution collect form web for “JVM release unused heap”

    First, this should really be a comment, but it’s going to be way to big probably. Question yourself if you really REALLY want to release memory from JVM back to the OS. Acquiring it back will be expensive, like probably more expensive then running your application as it is – it will slow you down.

    Then, your default collector under java-8 is Parallel GC, I am not very sure that those MinHeapFreeRatio and MaxHeapFreeRatio actually work with it. I have tried with G1GC – and it does, but did not with Parallel. Then adding the -Xmn might have been just luck/good timing; AFAIK it should not impact the other two parameters. this is a rather interesting answer to a similar question that you have.

    Docker will be the best open platform for developers and sysadmins to build, ship, and run distributed applications.