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JVM - heap, stack Size, # of threads

rameshaa
rameshaa asked
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Last Modified: 2013-11-23
Hi,

 How do I found default heap size, stack size for the
 thread, number of threads per process supported ?

 I tried with java -verbose but it didn't gave the
 info. what I expected ?

 and how the above things will vary for each OS and how
 do I found ? Is there any commands/utility available ?

 I also wanna know how many threads supported per process?

Thanx in advance,
Ramesha//
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Commented:
I believe the default heap size starts at 2 mb, and can grow to 64 mb.  If you need more than 64mb of heap, you need to specifiy the following flags:

  -Xms<size>   for minimium heap size
  -Xmx<size>   for maximum heap size

For example:

  -Xmx256m     wil get you 256 Mb of heap

Keep in mind that you don't necessarily want to allocate a large minimum heap, because that will cause the JVM to immediately grab that much memory from the OS.

If you want to set the size of the Java thread stack, use:

  -Xss<size>

The default is 512k.

As far as # of threads per process, that will depend on the OS you're running on, but most likely you will run out of memory before exhausting the number of possible threads...

Now, from a pragmatic standpoint:

1.  You shouldn't care about the default stack size, because if you're using too much stack, you've got a serious design flaw in your program.

2.  If you're creating enough threads where you have to worry about bumping into some type of maximum, you've got a serious design flaw in your program.

As far as I know, there is no command or utility that will give you this information on an OS by OS basis...

Commented:
you can try some java profiling tool like jprobe or optimizeit (you can download evaluation) to get a realtime look on your heap and threads

Commented:
Do you need more information?  If not, please close out  this question.
Please update and finalize this question.
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