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Is there  any Difference between heap dumps, core dumps,  thread dumps, memory dumps, java dumps, jvm dumps?

Posted on 2009-05-14
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Is there  any Difference between heap dumps, core dumps,  thread dumps, memory dumps, java dumps, jvm dumps?
what is use these things when and how to take these dumps ? what processes are available other than kill -3 pid? are there any tools that track these dumps? what can be inferred from the dumps analysis? how to take these dumps when a server fails and pid no more available?
what is the difference between  open threads, idle threads, thread count, thread pool? how to find these w.r.t a server?
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Question by:yuvasatta
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rajesh_bala earned 500 total points
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Well, too many questions in the same sections. :) ..Will try to answer.

1. Threaddump - These are taken to understand what threads are doing in JVM at any given point in time. It is done by sending ctrl+pause / kill -QUIT <pid>. This signal is handled by JVM and it dumps the thread information alnog with stack. This is mainly done to understand stuck threads, waiting threads, running threads and other such information. Sometimes lock information can also be obtained from this. But since JDK 1.5, lock information is getting tricker with threaddumps.

2. Core Dump/Heap Dump - When JVM exits, there is a high probability that it would create a core dump/heap dump in the directory. This is nothing but the heap representation of JVM. It can be opened easily with JProfiler, Yourkit etc and if JVM crashed due to memory leaks, this dump would be of great importance.

3. When no pid is available, its not possible to get the threaddump. no pid means that the process is not running...isnt that the case. :)

4. threads - The number of threads in the pool. Threadcount should give you the current threads in the thread pool. Thread pool is nothing but a way of maintaing a set of threasd so that it can be assigned whenever required (instead of creating a thread for every request which is time consuming and expensive).

Note: If possible, try to breakdown your questions and ask in multiple threads.
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by:yuvasatta
ID: 24394928
Thanks for explanation,
It helped me a lot.
I will break my questions in my next postings, if any
can please explain about the open threads and idle threads?
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by:rajesh_bala
rajesh_bala earned 500 total points
ID: 24395312
Not sure where you refer by "open threads". But "idle threads" refer to the number of free threads in  the pool which can accept new requests.

Are you referring to the "busy threads" as open threads? "Busy threads" are the ones in the pool which are currently doing work
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by:yuvasatta
ID: 24395349
can you please tell me how to find the open threads and idle threads w.r.t weblogic
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by:rajesh_bala
rajesh_bala earned 500 total points
ID: 24395389
Again for 8.x you have to refer to the documentation or use MBeans.

However, if its 9.x you can go to server --> monitoring --> threads

I believe something like this should be there in 8.x as well.
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by:yuvasatta
ID: 24395467
Thank you
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by:yuvasatta
ID: 24421762
I tried to find threads info from weblogic 8.x, but not able to.
any idea to find the threads in weblogic 8.x?
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by:rajesh_bala
rajesh_bala earned 500 total points
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In weblogic 8.x, its fixed number of threads you configure in config.xml. You can cehck in that alternatively.
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by:yuvasatta
ID: 24422728
ok thanks
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