JMap/JHat hex values (original) (raw)
Alan Bateman Alan.Bateman at oracle.com
Sat Jun 23 03:20:49 PDT 2012
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On 22/06/2012 21:10, Max Grossman wrote:
Hi all,
I'm curious if anyone can tell me about the hex values displayed on a jhat-generated page from a heap dump using jmap? I get a heap dump using: jmap -heap:format=b pid and then process it using jhat: One thing to know is that there are many ways to generate a HPROF heap dump:
With the built-in heap dump support, meaning "jmap -dump:file= " or -XX:+HeapDumpOnOutOfMemoryError.
With the serviceability agent on core files or hung processes, "jmap -F -dump:file= " or the undocumented jmap -heap:format=b option that you are using. Note that there is no guarantee that you will get a consistent heap dump when you use this approach, mostly because data structures and the heap may be in an inconsistent state.
With the HPROF agent when you specify the heap option.
For 1 & 2 then the the object ID of instances in the heap dump is the object address so you can make some inferences. For 3 then it's an ID assigned by the HPROF agent so will not be useful to what I suspect you are doing.
-Alan.
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