Difference between javacore thread dump and heap dump in Websphere

Question

Can someone tell me the exact difference between javacore  thread dump and heap dump  Under which situation each of these are used

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A Thread dump is a dump of all threads s stack traces  i e  as if each Thread suddenly threw an Exception and printStackTrace ed that  This is so that you can see what each thread is doing at some specific point  and is for example very good to catch deadlocks   A heap dump is a  binary dump  of the full memory the JVM is using  and is for example useful if you need to know why you are running out of memory - in the heap dump you could for example see that you have one billion User objects  even though you should only have a thousand  which points to a memory retention problem

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JVM head dump is a snapshot of a JVM heap memory in a given time  So its simply a heap representation of JVM  That is the state of the objects   JVM thread dump is a snapshot of a JVM threads at a given time  So thats what were threads doing at any given time  This is the state of threads  This helps understanding such as locked threads  hanged threads and running threads   Head dump has more information of java class level information than a thread dump  For example Head dump is good to analyse JVM heap memory issues and OutOfMemoryError errors  JVM head dump is generated automatically when there is something like OutOfMemoryError has taken place   Heap dump can be created manually by killing the process using kill -3   Generating a heap dump is a intensive computing task  which will probably hang your jvm  so itsn t a methond to use offetenly  Heap can be analysed using tools such as eclipse memory analyser   Core dump is a os level memory usage of objects  It has more informaiton than a head dump  core dump is not created when we kill a process purposely

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Heap dumps anytime you wish to see what is being held in memory Out-of-memory errors Heap dumps - picture of in memory objects - used for memory analysis Java cores - also known as thread dumps or java dumps  used for viewing the thread activity inside the JVM at a given time  IBM javacores should a lot of additional information besides just the threads and stacks -- used to determine hangs  deadlocks  and reasons for performance degredation System cores

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Thread dumps are javacore show snapshot of threads running in JVM  it is useful to debug hang issues  it will provide info about java level dead locks and also IBm version of javacores provides much more useful information  such as heap usage  CPU usage of each thread and overall heap usage along with number of classes laded by the JVM   Heapdumps  provides information about Java heap usage by an JVM  which can be used to debug memory leaks  Heapdumps are generated by IBM JVMs when a JVM is runs into outofmemoryerror  Heapdumps are only for heap leaks in java  native out of memory error may result system dumps usually with an  GPF  General protection Fault

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A thread dump is a dump of the stacks of all live threads  Thus useful for analysing what an app is up to at some point in time  and if done at intervals handy in diagnosing some kinds of   execution  problems  e g  thread deadlock    A heap dump is a dump of the state of the Java heap memory  Thus useful for analysing what use of memory an app is making at some point in time so handy in diagnosing some memory issues  and if done at intervals handy in diagnosing memory leaks   This is what they are in  raw  terms  and could be provided in many ways  In general used to describe dumped files from JVMs and app servers  and in this form they are a low level tool  Useful if for some reason you can t get anything else  but you will find life easier using decent profiling tool to get similar but easier to dissect info   With respect to WebSphere a javacore file is a thread dump  albeit with a lot of other info such as locks and loaded classes and some limited memory usage info  and a PHD file is a heap dump   If you want to read a javacore file you can do so by hand  but there is an IBM tool  BM Thread and Monitor Dump Analyzer  which makes it simpler  If you want to read a heap dump file you need one of many IBM tools  MDD4J or Heap Analyzer

[java] Difference between javacore, thread dump and heap dump in Websphere

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