Does anybody know if there is any documentation about the VM options starting with "-XX:" and, if yes, where ?

 

 

This is the link I have....

http://java.sun.com/docs/hotspot/VMOptions.html

 

 

Sweet.

There seem to be some missing though, like

-XX:MaxDirectMemorySize

 

 

See appendix A5:
http://developers.sun.com/techtopics/mobility/midp/articles/garbagecollection2/#a.5

 

 

Heh. The "-X" options are the documented undocumented options, while the "-XX" options are the undocumented undocumented options :-).

Seriously, Sun has an extremely schizophrenic outlook when it comes to these options. On the one hand, "java -XX" doesn't spit out the list of -XX options available, but then they have these little documentation teases scattered around their sites where they (implicitly) encourage you to use them.

-XX:NewSize and -XX:MaxNewSize must be the most popular undocumented options on Earth..

 

 

Hi
You will be surprised in the number of -XX options. Another area will the system properties that u can set to turn this on, turn that off... Areas like in the network/awt...

 

 

can u say a little more about those :) ?

 

 

Hi
Too many to go thru...
Here are some that I used to troubleshoot hotspot crashes
-Xcomp
Compile on 1st invocation

-Xbatch
Prevents overlapped compilation and execution.

-XX:+PrintCompilation
print which method is the hotspot compiling

-XX:+ShowMessageBoxOnError
Will pause VM before crashing, can gcore process before exiting.

Well, the rest... the rest... when u need it, it will be documented ;)

 

 

here is my email fipilica@yahoo.com. When u have the time maybe you will email me one copy of that list ;)

Thx and have a nice day!

 

 

Hi,

a really interesting one is -XX:MinHeapFreeRatio=nnn as by default the VM reserves FOURTY !!! percent more memory than it really needs.

 

 

Actually that extra 40% is the space left free after a collection and is used
for future allocations. Without it (or some amount) the next allocation would fail
and force another collection.