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java heap size is only 20MB, but memory usage is 1.7GB [message #531935]

Thu, 06 May 2010 10:37

John Ye
Messages: 19
Registered: July 2009

Junior Member

Hi there,

I am running a java program on Windows Vista with Java 1.6. I am using -Xmx128m. But the memory is growing to 1.7GB.

The heap dump only shows less than 20MB. So memory must be used outside java. It could be jni, but I am not aware of any.

What are other possibilities?

Any suggestions are appreciated.

Thanks,
John

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Re: java heap size is only 20MB, but memory usage is 1.7GB [message #532089 is a reply to message #531935]

Fri, 07 May 2010 03:18

Krum Tsvetkov
Messages: 146
Registered: July 2009

Senior Member

>> What are other possibilities?
One other possibility is threads - there is some space reserved outside ot the java heap for their stacks. Just check the number of threads via jconsole or in a thread dump.

>> It could be jni, but I am not aware of any.
Even if you don't use jni on your own, jni is used in the JDK classes, for example when working with Zips, nio, ...

Just googled for leaks in zip and found this:
http://bugs.sun.com/view_bug.do?bug_id=6734186

I believe I have very little chance to hit the proper problem by just gessing like this, but you can probably find something more specific based on your appplication knowledge.

Hope this helps a bit.

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Re: java heap size is only 20MB, but memory usage is 1.7GB [message #534024 is a reply to message #531935]

Mon, 17 May 2010 14:12

Gary Karasiuk
Messages: 12
Registered: July 2009

Junior Member

The Java heap is only one part of the process's memory (but for most Java applications it is usually the largest part).

Native memory is also needed for the byte codes, native JVM structures, threads, DLLs, etc.

There is an excellent tool called vmmap
http://technet.microsoft.com/en-us/sysinternals/dd535533.asp x
that will show you all of the allocated memory.

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Re: java heap size is only 20MB, but memory usage is 1.7GB [message #534697 is a reply to message #531935]

Wed, 19 May 2010 21:27

John Ye
Messages: 19
Registered: July 2009

Junior Member

Krum and Gary,

Thanks for replying to my question. Very helpful information. I will take a look and see if I can narrow the problem down.

Best,
John

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