garodriguezlp / jvm-memory-management

JVM Memory Management

Examples and practices for the talk on JVM Memory Management basics given to my colleagues at Perficient in August 2022

Prerequisites

Most of the examples are written with jbang

There are multiple ways to install jbang on your machine, but here are the options in case you don't want to install it.

• Powershell:

  iex "& { $(iwr https://ps.jbang.dev) } [jbang arguments]"

• GitBash/cygwin/mingwin/WSL:

  curl -ls https://sh.jbang.dev | bash -s - [jbang arguments]

Heap and Stack in Action

The following oneliners assume that you have the idea binary in your $PATH. If vscode is your preferred editor, you can use --open=code instead

jbang edit --open=idea StackAndHeap@garodriguezlp/jvm-memory-management

Intro into GC

If you want to know what's jbang doing under the hood, you can use the --verbose flag

Other java versions could be chosen by using the --java flag. Example: --java 11. See jbang docs

• Running it with Java 8

  jbang run `
    --java 8 `
    --java-options='-verbose:gc' `
    IntroGarbageCollection@garodriguezlp/jvm-memory-management

• Running it with Java 8 limiting max heap, then run it with --java 11 and see the difference after the last GC. The thing here is that GC in Java 11 is capable of giving back memory to the OS

  jbang run `
    --java 8 `
    --java-options='-verbose:gc' `
    --java-options='-Xmx127m' `
    IntroGarbageCollection@garodriguezlp/jvm-memory-management

• Running it with Java 8 limiting max and min heap

  jbang run `
    --java 8 `
    --java-options='-verbose:gc' `
    --java-options='-Xms127m' `
    --java-options='-Xmx127m' `
    IntroGarbageCollection@garodriguezlp/jvm-memory-management

• Running visualvm could be executed like this if $JAVA_HOME and $VISUALVM_HOME environment variables are properly set (install the Visual GC plugin first)

  & $env:VISUALVM_HOME\bin\visualvm.exe --jdkhome $env:JAVA_HOME --console suppress

Memory Leak

• Run the following jbang powered class

  jbang run `
    --java 11 `
    --java-options='-verbose:gc' `
    --java-options='-Xmx256m' `
    --java-options='-XX:+HeapDumpOnOutOfMemoryError' `
    MemoryLeak@garodriguezlp/jvm-memory-management

• Open visualvm and connect to the process (don't forget to install the Visual GC plugin)

  & $env:VISUALVM_HOME\bin\visualvm.exe --jdkhome $env:JAVA_HOME --console suppress

• Open Eclipse Memory Analyzer tool and load the heap dump file

  & $env:MAT_HOME\eclipsec.exe