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

[Y. Srinivas Ramakrishna]

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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