Java using much more memory than heap size (or size correctly Docker memory limit)

Question

For my application, the memory used by the Java process is much more than the heap size.

The system where the containers are running starts to have memory problem be

Answer 1

Java needs a lot a memory. JVM itself needs a lot of memory to run. The heap is the memory which is available inside the virtual machine, available to your application. Because JVM is a big bundle packed with all goodies possible it takes a lot of memory just to load.

Starting with java 9 you have something called project Jigsaw, which might reduce the memory used when you start a java app(along with start time). Project jigsaw and a new module system were not necessarily created to reduce the necessary memory, but if it's important you can give a try.

You can take a look at this example: https://steveperkins.com/using-java-9-modularization-to-ship-zero-dependency-native-apps/. By using the module system it resulted in CLI application of 21MB(with JRE embeded). JRE takes more than 200mb. That should translate to less allocated memory when the application is up(a lot of unused JRE classes will no longer be loaded).

Here is another nice tutorial: https://www.baeldung.com/project-jigsaw-java-modularity

If you don't want to spend time with this you can simply get allocate more memory. Sometimes it's the best.