G1: SoftReference, 0 refs, 31.0027203 secs

[Simone Bordet]

Hi,

I have an application that reported very large (around 30 s) times to
process *zero* SoftReferences, for example:

6015.665: [SoftReference, 0 refs, 23.0169525 secs]6038.682:
[WeakReference, 1 refs, 0.0046033 secs]6038.687: [FinalReference,
31647 refs, 0.0090301 secs]6038.696: [PhantomReference, 241 refs,
0.0048419 secs]6038.701: [JNI Weak Reference, 0.0000463 secs],
23.2166772 secs]

We have been hit by this anomaly a few times now, and in the attached
logs (that also show the command line flags) it happened 3 times: at
uptimes 6015.512, 6074.487, 6141.161.

What happens after these long pauses is that G1 goes into "GC overhead
mode", tries to expand the heap (which fails because it's already
expanded), but keeps the Eden at a very small size, resulting in a
series of back-to-back collections that lasted almost 3 minutes where
the MMU dropped making the application almost unusable.
After that, G1 was able to recover to normal behavior.

I was wondering if anyone knows a little more about this issue (long
times to process zero soft references), or whether it has been fixed
in more recent releases.

We are not aware of any other process that could have caused this such
as busy disk I/O or swapping (the machine has plenty of memory left
and it is dedicated to the JVM), but we'll run jHiccup next time.
However, the fact that it always happened during the processing of
soft references seems suspicious.

Should I file an issue ?

Thanks !

-- 
Simone Bordet
http://bordet.blogspot.com
---
Finally, no matter how good the architecture and design are,
to deliver bug-free software with optimal performance and reliability,
the implementation technique must be flawless.   Victoria Livschitz
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