Java6 vs Java5

[Shaun Hennessy]

'll keep an eye out for 6u14 for the Perm option and thanks
for confirming no STW options -- I didn't think there was any but I'd
gotten all googled out and figured I'd just ask.

thanks,
Shaun




Jon Masamitsu wrote:
> Shaun Hennessy wrote On 03/27/09 11:20,:
>
>   
>> A few quick questions I'm hoping someone can help me with...
>> (I'm running Java6u12)
>>
>> 1) Is there any plans for the new option 
>> CMSInitiatingPermOccupancyFraction (CR 6634032)
>> to put into Java6?  (The fixed in listed as hs13(b01) - I'm not sure 
>> what this is - Java7?)
>>  
>>
>>     
>
> This change will make it to a 6 update.  Probably 6u14.
>
>   
>> 2) Was there a change in the default CMS initiating occupancy from Java5 
>> to Java6 (68% to 92%)
>> when using CMS?
>>  
>>
>>     
>
> Unless explicitly set on the command line the initiating occupancy is
> calculated
> from other parameters (MinHeapFreeRatio and MinHeapFreeRatio) and
> I don't think those latter changed between 5 and 6.  Other CMS
> parameters changed.
>
> http://java.sun.com/javase/6/docs/technotes/guides/vm/cms-6.html
>
>
>   
>> 3a) If using the Throughput GC -- our old-gen will be triggered when 
>> it's full right? There's no need
>> to have it go earlier as we're going to stop-the-world....   Nothing 
>> would be different java5 vs java6?
>>  
>>
>>     
>
> Yes, with the throughput collector (and indeed with all the stop the world
> (aka STW) collectors), a collection is started when a generation is full.
>
>   
>> 3b) - If I am going to the throughput collector, is there anyway to 
>> force the application to keep
>> a certain amount of the heap free (ie -Xms=Xms=256M --) I always want to 
>> get say 100M free
>> so once the free heap drop to that level trigger a GC?  (Basically I 
>> want a CmsInitiatingOccupancyFraction
>> but for the throughput collector)
>>  
>>
>>     
>
> There is no JVM option that will allow you to request that
> a certain amount be kept free with the STW collectors.
>
>   
>>  
>>
>>     
>
>