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Eden v Old [message #10229] Sun, 03 May 2009 22:57 Go to next message
Michael is currently offline MichaelFriend
Messages: 1
Registered: July 2009
Junior Member
Is there any way to identify which objects are in Eden versus Survivor
spaces v Tenured space?

And/or get the object copy count? (i.e the counter of the number of times
the object has survived GC in the young generation).

I'm attempting to identify what's causing the generation-0 garbage
collection to take so long.
Re: Eden v Old [message #10295 is a reply to message #10229] Tue, 05 May 2009 19:56 Go to previous message
Andreas Buchen is currently offline Andreas BuchenFriend
Messages: 113
Registered: July 2009
Senior Member
Hi Michael,

sorry, bad news, the heap dump neither contains the info about the space
the object is in (also not if the String is in perm) nor an object copy
count. With a heap dump only you will have problems to figure this out.

Maybe take a look at the number of weak and soft references. Many of those
references increase the stop-the-world time, because the VM has to decide
at one point or another whether to mark the objects "behind" the refrence
or not. From what I understand, this has to be done in sync with all gc
threads.

In the OQL pane, you could run "SELECT * FROM INSTANCEOF
java.lang.Reference" to see all those references currently in the heap.
Also the "Java Basics" -> Reference statistics queries can give you an
overview of what those references currently keep alive.

The other point to look into are finalizers. As you probably, finalizers
always require 2 full gc to actually free up the space. Again, the "Java
Basics" category also contains a query which displays finalizers and
what's in the queue.



Hopefully I could give you some hints,


Andreas.
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