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JVM Arguments

JVM arguments list(partial):

  • -Xms, minimum heap memory
    • Example: -Xms20m
  • -Xmx, max heap memory
    • Example: -Xmx20m
  • -XX:+HeapDumpOnOutOfMemoryError, let JVM dump current memory snapshot when out of memory
  • -Xss, max stack size, different on OS
    • Example: -Xss128k. Recursive call or define more local arguments.

  • -XX:PermSize, -XXMaxPermSize

    • only take effect below JDK6
    • from JDK 7, String constant moved from perm generation to Java heap. From JDK 8, perm generation has been replaced by metaspace

    • The following code will print "true", "true" in JDK 6, print "true", "false" in JDK 7 and later.

      Java
      String str1 = new StringBuilder("computer").append("software").toString();
System.out.println(str1.intern() == str1);

String str2 = new StringBuilder("ja").append("va").toString();
System.out.println(str2.intern() == str2);

  • -XX:MaxMetaspaceSize, set the max size of the metaspace. Default -1 no limitation.

  • -XX:MetaspaceSize, set the initial size of the metaspace, the unit is bytes. If the used size exceeds this size, will trigger GC and size adjustment:
    • If released a lot of space, then decrease this value
    • If released space is low, then increase this value(not exceeds the max value)
  • -XX:MinMetaspaceFreeRation, set the minimal ration of the free space
  • -XX:MaxMetaspaceFreeRation, set max ration of the free space
  • -XX:MaxDirectMemorySize, set the max direct memory size. The default is the same as the -Xmx.
  • -verbose verbose GC
    • Example: -verbose:class
  • -XX:+TraceClassLoading
  • -XX:+TraceClassUnLoading(only in debug JVM)