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From Kevan Miller <kevan.mil...@gmail.com>
Subject Re: large-scale app.. random spiking on even static files!
Date Wed, 13 Aug 2008 00:32:08 GMT

On Aug 12, 2008, at 2:21 PM, pc3 wrote:

>
> How does this look in terms of my GC settings?
>
> Note the Full GC taking 7-9 sec... and yes, our users are feeling it.
>
> 9294.839: [Full GC [PSYoungGen: 5669K->0K(518848K)] [PSOldGen:
> 2270713K->2036966K(3495296K)] 2276382K->2036966K(4014144K) [PSPermGen:
> 132633K->132553K(262144K)], 9.6645590 secs]

<snip>

> Kevan Miller wrote:
>>
>>
>> On Aug 9, 2008, at 12:09 AM, Pete Clark wrote:
>>
>>> Finally, here are our startup opts as it pertains to GC if it helps:
>>>
>>> -XX:+HeapDumpOnOutOfMemoryError -XX:PermSize=256m - 
>>> XX:MaxPermSize=256m
>>> -Xmx5120m -Xms5120m -Xss128k -XX:ParallelGCThreads=20
>>> -XX:+UseConcMarkSweepGC -XX:+UseParNewGC -XX:SurvivorRatio=8
>>> -XX:TargetSurvivorRatio=90 -XX:MaxTenuringThreshold=31
>>> -XX:+AggressiveOpts -Xloggc:/var/tmp/gc.log

<snip>

What's the behavior like, if you run without the GC tuning parameters?  
Wondering how much these tuning parms are actually buying you... E.g:

-XX:+HeapDumpOnOutOfMemoryError -XX:PermSize=256m -XX:MaxPermSize=256m  
-Xmx5120m -Xms5120m -Xss128k -Xloggc:/var/tmp/gc.log

Do you have any very large objects? How much physical memory do your  
servers have?

I doubt that 20 parallel GC threads are necessary, but also doubt that  
they are causing any harm...

As I mentioned, I'm not really up-to-speed with current (1.5/1.6) GC  
tuning parameters/behaviors. One thing to explore is how to keep  
objects out of your tenured space (and in young space). Hmm. Have you  
tried -XX:+UseParallelOldGC?

I assume your problem is in the GC of your tenured space (but that's  
kind of a big assumption... ;-)

--kevan

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