javaheap-size

Changing maximum java heap size

As it is described in many sources I am trying to use java -Xms512m from the command line in order to set maximum size of heap for java machine to 512 Mb. But something goes wrong and command line shows the following
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And, as I checked directly from the program: long heapMaxSize = Runtime.getRuntime().maxMemory(); heapMaxSize is equal to 954728448 which is about 1Gb.

Solution

  • This is called a VM parameter, and must be specified when you start your VM (the JVM).

    You may specify the maximum heap size as you run your program:

    java -Xmx1024m -jar yourJar.jar

    Or alternatively, you can set an environment variable on your system JAVA_OPTS and the JVM will respect your settings as it starts:

    JAVA_OPTS="-Xmx1024m"

    Regarding your second question, I would refer you to What are Runtime.getRuntime().totalMemory() and freeMemory()? as it clarifies what values are returned by Runtime.getRuntime().maxMemory() and friends.