forgot to attach. Regards, Kirk Tony Printezis wrote:
Well, I was going to pointer the finger towards the class loaders... but Kirk here did a much more thorough analysis! :-)
Tony
kirk wrote:
Hi Jed,
I've had a quick look at the heap dump. I'm having a little trouble understanding what is in there. What I can see is a large number of java.lang.reflect.Method objects being held. There seems to be two competing patterns of references holding onto these objects. I've attached some screenshots rather than use words.
The scary thing is that the references include ClassLoader.scl, JDK12Hooks.systemClassLoader as well as Apache commons logging LogFactory. With this type of the complex entanglement it would seem unlikely that these objects would ever be collected. The other pattern also includes the spiders web of references. It also includes UberspecImpl and a whole bunch of static collections. IME, static collections are involved in the vast majority of leaks I've diagnosed.
Interestingly enough the a portion of the 2nd largest consumer of memory is also tangled up in the JDK12Hooks. Random sampling leads me to AST parse trees and "no reference". Looks like much of this is tied up with Velocity. In fact the largest consumer of memory at 24% is char[]. I'm failing to find anything that is not tied up with Velocity (AST parsing).
Needs more investigation. Be interesting to run a test with generations turned on. NetBeans generations is a true count unlike that provided by YourKit.
Regards, Kirk
Jed Wesley-Smith wrote:
Classes as well. We end up getting an OOME although the profilers report only a third of the heap is reachable.
Although I indicated we saw this on the IBM jdk analysis of that dump showed a completely different issue that apparently may not be a problem (due to reflection optimisation on that jdk) - the dead objects appear to have been correctly cleared. We are reproducing this to verify.
Additionally we tried running with -client on the sun jvms as we saw a bug that might have caused it reported against server only but without success.
cheers, jed.
On 16/04/2009, at 12:51 AM, Tony Printezis <Antonios.Printezis@sun.com> wrote:
OK, I'll bite.
When you say: "a large section of memory (a plugin framework)" do you mean only objects in the young / old gen, or also classes in the perm gen?
How do you know that said memory is not being reclaimed? Do you eventually get an OOM?
Given that it happens with two different JVMs (I assume you use HotSpot on Linux and Mac, as well as the IBM JDK), it's unlikely to be a GC bug, as both JVMs would need to have the same bug. Not impossible, but unlikely, IMHO.
Tony
Jed Wesley-Smith wrote:
all,
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 instance?
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: http://jira.atlassian.com/browse/JRA-16932
Having come to the end of our tethers here, if anyone can help in any way it would be massively appreciated.
cheers, Jed Wesley-Smith JIRA Team @ Atlassian
-- --------------------------------------------------------------------- | Tony Printezis, Staff Engineer | Sun Microsystems Inc. | | | MS UBUR02-311 | | e-mail: tony.printezis@sun.com | 35 Network Drive | | office: +1 781 442 0998 (x20998) | Burlington, MA 01803-2756, USA | --------------------------------------------------------------------- e-mail client: Thunderbird (Linux)
