Parallel GC thread priority

Azeem Jiva azeem.jiva at oracle.com
Fri Sep 7 15:39:51 UTC 2012


I had not thought about other processes, which is a possibility. 
Although raising the priority of the GC threads won't help which I 
believe what Dmytro was suggestion.


On 09/07/2012 10:35 AM, Vitaly Davidovich wrote:
>
> You can have other threads from different processes in the system 
> competing though.
>
> However, such a large wall time vs CPU time can also be caused by 
> heavy swapping on a slow disk.  The heap there doesn't look all that 
> big though ...
>
> Sent from my phone
>
> On Sep 7, 2012 11:21 AM, "Azeem Jiva" <azeem.jiva at oracle.com 
> <mailto:azeem.jiva at oracle.com>> wrote:
>
>     The Parallel collector is a stop-the-world collector.  The Java
>     threads are suspended until the GC finishes.  I think your
>     survivor spaces maybe mis-configured, and that's why you're seeing
>     such large GC times.
>
>
>     On 09/07/2012 10:17 AM, Dmytro Sheyko wrote:
>>     Hi,
>>
>>     I can see that Parallel GC works on threads with NormPriority,
>>     while CMS and G1 threads run with NearMaxPriority. This probably
>>     not an issue if java application works alone, but some time ago I
>>     observed GC log like this (it was Jenkins CI on Windows):
>>
>>     [Full GC [PSYoungGen: 10352K->0K(171904K)] [PSOldGen:
>>     403417K->114637K(415872K)] 413769K->114637K(587776K) [PSPermGen:
>>     76315K->76315K(83968K)], 30.2595731 secs] [Times: user=0.77
>>     sys=0.41, real=30.26 secs]
>>
>>     Despite cpu time for GC was just 1.18 sec (= 0.77 + 0.41), the
>>     real time was 30.26 sec! It seems to me that the system was busy
>>     that time and GC threads was starving.
>>
>>     If we could raise priority of Parallel GC threads, other
>>     application would have less impact on GC duration.
>>
>>     What do you think?
>>
>>     Thanks,
>>     Dmytro
>
>     -- 
>     Azeem Jiva
>     @javawithjiva
>

-- 
Azeem Jiva
@javawithjiva

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