Java Virtual Machine
====================


This document gathers technical informations about the Java VM to help
Java/Scala developers tuning their runtime settings on the Java VM.


VM Options
----------

* -Xmx option (maximum heap size)

   Heaps larger than 2GB are available starting with J2SE 1.3.1

   Default: 64M (32-bit UNIX and Windows)

* -Xms option (initial heap size)

   Minimum: 1025K (Linux-i586, Solaris-i586), etc.. (see [vm08])
   Default: 2M (32-bit UNIX and Windows)

* -Xss option (thread stack size)

   Minimum: 48K (Linux-i586), 64K (Solaris-i586), etc.. (see [vm08])
   Default: 256K (32-bit UNIX and Windows)

   NB. Stack size under Windows is a link-time setting, so the executable
       (java.exe) as created by Sun has this 256K limit built in. Windows
       however, has a simple utility to modify the stack space of an
       executable (see [vm03]).
       In a command window (or Cygwin shell), use the EDITBIN command to
       permanently modify the executable (WARNING! Do not reduce the stack
       size below 32K, see [vm04])

       EDITBIN /STACK:16000000 C:\Path\To\java.exe


Resources
=========

VM Options and Tools
--------------------

[vm01] Some useful -XX options
       http://java.sun.com/javase/technologies/hotspot/vmoptions.jsp

[vm02] jvmstat 3.0
       http://java.sun.com/performance/jvmstat/

[vm03] Modify the actual java.exe executable on Windows
       http://www.eyesopen.com/docs/html/javaprog/node7.html

[vm04] Configuring server stack size
       https://ssa.usyd.edu.au/docs/eassag/eassag20.htm

[vm06] Tuning the Java Runtime System
       http://docs.sun.com/source/817-2180-10/pt_chap5.html

[vm07] JVM Tuning
       http://www.caucho.com/resin-3.0/performance/jvm-tuning.xtp

[vm08] Java HotSpot: load the VM from a non-primordial thread and effects
       on stack and heap limits.
       http://blogs.sun.com/ksrini/entry/hotspot_primordial_thread_jni_stack

Garbage Collection
------------------

[gc01] Tuning Garbage Collection with the 5.0 Java[tm] Virtual Machine
       http://java.sun.com/docs/hotspot/gc5.0/gc_tuning_5.html

[gc02] Tuning Garbage Collection with the 1.4.2 Java[tm] Virtual Machine
       http://java.sun.com/docs/hotspot/gc1.4.2/

[gc03] Tuning Garbage Collection with the 1.3.1 Java[tm] Virtual Machine
       http://java.sun.com/docs/hotspot/gc/

[gc04] Garbage Collector Ergonomics
       http://java.sun.com/j2se/1.5.0/docs/guide/vm/gc-ergonomics.html


mics/20-Apr-2007