the amazing tales of the search for the invisible man! or, where's my gc root
jed at atlassian.com
Mon Apr 13 21:53:20 PDT 2009
I am writing to this list in some desperation hoping for some expert
advice. We (the JIRA development team at Atlassian) have been hunting
memory leaks for some weeks and in the process have tracked down and
removed every possible reference to a large section of memory (a plugin
framework) that we could find. Starting with all strong references and
proceeding to remove soft and weak references - even things like
clearing the java.lang.reflect.Proxy cache - and even Finalizer
references until both YourKit, Eclipse MAT, JProfiler and jhat all
report that the memory in question is dead and should be collectable,
but inexplicably _the JVM still holds on to it_. There are no JNI Global
references either, yet this memory remains uncollectable!
This happens for the 1.5 and 1.6 JVMs on Linux and Mac, and the IBM 1.6
JDK on Linux.
So my question is, how on earth do I search for what is referencing this
uncollectable memory? Are there any other tools that can help find why
this memory is not collected? Can I query the VM directly somehow?
I fear this is a JVM GC bug as no known memory analysis tool can find
the heap root (i.e. according to "the rules" there is no heap root). Are
there any known GC memory leaks caused by ClassLoaders being dropped for
The application is creating and disposing of a lot of ClassLoaders via
OSGi (Apache Felix) with Spring OSGi. It creates a lot of
java.lang.reflect.Proxy class instances.
We have written this up and added an example heap dump here:
Having come to the end of our tethers here, if anyone can help in any
way it would be massively appreciated.
JIRA Team @ Atlassian
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