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MAT not showing entire HEAP ? [message #8563] Mon, 19 January 2009 21:13 Go to next message
chamaster  is currently offline chamaster Friend
Messages: 2
Registered: July 2009
Junior Member
Hello,
I have this strange behaviour : when jmap creates a 1.7go heap dump from
my production server, MAT only shows :
Size: 349,7 MB Classes: 27k Objects: 6,6m Class Loader: 11,3k in
Overview/Details when open it up.
Is it so that the remaining 1.4 is free and available to allocate more
objets ?
I am running Probe into Tomcat (5.5.26). Probe shows approx. 80% of used
memory.
Can someone help me understand where my memory is going...

Thanks in advance

Anthony.
Re: MAT not showing entire HEAP ? [message #8581 is a reply to message #8563] Tue, 20 January 2009 12:11 Go to previous message
Andreas Buchen is currently offline Andreas BuchenFriend
Messages: 113
Registered: July 2009
Senior Member
> I have this strange behaviour : when jmap creates a 1.7go heap dump from
> my production server, MAT only shows :
> Size: 349,7 MB Classes: 27k Objects: 6,6m Class Loader: 11,3k in

Hi Anthony,

when a heap dump is written, MAT removes objects which are not reachable
anymore. The reason is this: depending on the algorithm, the garbage
collector actually leaves some garbage behind. For example, some objects
are converted into pseudo byte arrays in order to avoid moving and
re-addressing objects.

However, this "waste" is usually only about 3 to 4 per cent of the heap.

You can print a class histogram of the removed objects following these
instructions: https://bugs.eclipse.org/bugs/show_bug.cgi?id=245410#c1


There could possible more reasons: sometimes the VM does not write a
complete heap dump. And, of course, it could also be a bug. And then we
would like to fix the problem. So if you run into many objects being
removed, it would be great to get my hands on the dump.

Let me know if you have further questions.

Kind regards,

Andreas.
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