CMS does not want to run concurrently

Michael Bien mbien at
Wed Dec 17 12:34:45 PST 2008

thank you both for the fast replies,

I will try all suggestions tomorrow. The App is already in production 
this means it is only possible to reboot at night. I will also add a 
full gc log and try to update to latest JDK 5 update release.

thanks for the support, I already learned a lot through your answers


Y Srinivas Ramakrishna schrieb:
> oh and, as Jon suggested before, it might  be a good
> idea to tack on -XX:+DisableExplicitGC to ensure that
> it's not RMI or other modules calling system.gc() here,
> unbeknownst to you. (If nothing else but to get closer to the
> root cause of the puzzling full gc's.)
> -- ramki
> ----- Original Message -----
> From: Y Srinivas Ramakrishna <Y.S.Ramakrishna at Sun.COM>
> Date: Wednesday, December 17, 2008 12:12 pm
> Subject: Re: CMS does not want to run concurrently
> To: Jon Masamitsu <Jon.Masamitsu at Sun.COM>
> Cc: hotspot-gc-use at
>> Just a quick remark related to:-
>> ...
>>> Here in the CMS gen (old generation) it is only 325384K full (out of
>>> a total of 659140K) when the collection starts.  Actually, you might
>>> have a severely fragmented heap.  In that case Full GC's would happen
>>> and using the survivor spaces would help.
>> When you have a fragmented heap that causes a full collection
>> the gc log message (in 5u8) would look a bit different as a
>> scavenge is first attempted, but fails because of a fragmented
>> heap, and then bails to a full collection. Because I do not see
>> that abortive scavenge attempt logged here, I suspect this may not
>> be a fragmentation-induced full gc, but perhaps something
>> else. Nonetheless, Jon's suggestion of using survivor spaces
>> to stem the tenuring of very young objects would be a good
>> thing to reduce fragmentation and other stresses on CMS.
>> -- ramki
>> _______________________________________________
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>> hotspot-gc-use at
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