Fully disable GC - no pauses - run with massive heap until outofmemory

[Tony Printezis]

Ramki,

Yes, you can set thresholds and get notifications, but I think you're 
right; said thresholds are only checked before / after a GC.

Tony

Y. Srinivas Ramakrishna wrote:
> On 02/03/10 16:07, Tony Printezis wrote:
>   
>> Hi Anthony,
>>
>> I hope you are well!
>>
>> An alternative is to use an MBean and monitor the occupancy of the eden. 
>> When that goes over a certain threshold, you can somehow kill the JVM. 
>>     
>
> Is there a threshold monitor that will look at generation occupancy
> _before_ a GC which is what you'd want here, right? I was always
> under the impression these detected occupancy after a GC and
> only then would sound the alarms; but perhaps there are options
> that specify precise behaviour in this regard.
>
> Mandy, cc'd, would know for sure. (Don't know where the spec is.)
> -- ramki
>
>
>   
>> In fact, you can be a bit more graceful this way, since you can notice 
>> early-ish that the JVM will run out of memory a bit into the future and 
>> shutdown all processing gracefully (i.e., let the current Tx complete), 
>> while redirecting new requests to a new JVM.
>>
>> Are you going to have any long-lived data in the JVM? Maybe, size the 
>> old generation large enough to accommodate it and after initialization 
>> do a System.gc() to move all that into the old generation. That way, 
>> you'll start processing with a totally empty eden.
>>
>> GC group: should we really be encouraging this? :-)
>>
>> Tony, HS GC Group
>>
>> Y. Srinivas Ramakrishna wrote:
>>     
>>> Hello Anthony --
>>>
>>> On 02/03/10 14:43, anthony.warden at nomura.com wrote:
>>>   
>>>       
>>>> How best to do this please?
>>>>
>>>> Command line options / hack the gc thread etc.
>>>>     
>>>>         
>>> Shape the heap so as to give all (or most) of it to the young gen,
>>> use no survivor spaces. For example, say you want a 32 G heap.
>>> Let's give 4 M to the old gen may be. So you could do:-
>>>
>>>    -Xmn32g -Xmx(32*1024+4)m -Xms(32*1204+4)m -XX:SurvivorRatio=1g
>>>
>>> (of course you use the computed values of the expressions in parentheses above.)
>>>
>>> Unfortunately, this will not give you an OOM when the heap gets
>>> full. It'll trigger a scavenge. If you want to give up the ghost at
>>> the first scavenge you can (if you are running on Solaris for example)
>>> write a Dtrace script to detect the invocation of a GC and kill
>>> the JVM process. Don't know if that's the behaviour you seek here.
>>>
>>> -- ramki
>>>
>>>   
>>>       
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>>>>
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