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Posted to jdo-dev@db.apache.org by Erik Bengtson <er...@jpox.org> on 2006/05/24 16:21:27 UTC

huge volumes and flush


Hi,

In case of huge amount of objects loaded /persisted, the flush method is for
this purpose. I wonder how the cache/state management can be implemented
without breaking JDO contract and capable to handle load, any tips?

Thanks

Erik Bengtson

Re: huge volumes and flush

Posted by Michael Bouschen <mb...@spree.de>.

Hi Erik,

most probably you know already: class WeakHashMap from java.util does 
not help when implementing the map of flushed instances. The WeakHashMap 
uses a WeakReference for the key, but it strongly references the value 
which is the flushed instance in your case. You need a map 
implementation that maintains a strong reference to the key, but a weak 
reference to the value. Just in case you are interested: there is a 
tested implementation in the core20 module of the apache jdo repository. 
The class is called WeakValueHashMap and you find it under 
core20/src/java/org/apache/jdo/util.

Regards Michael
> Thanks Craig,
>
> I works now.
>
> Quoting Craig L Russell <Cr...@Sun.COM>:
>
>   
>> Hi Erik,
>>
>> Generally, use weak references to persistent instances so they can be
>> garbage collected when the user no longer holds a strong reference to
>> them. Unflushed dirty instances need to be referenced strongly so
>> they are not garbage collected. So at flush time, move the flushed
>> dirty instances from a strong-reference map to a weak-reference map
>> (key = oid, value = weak-reference object).
>>
>> Craig
>>
>> On May 24, 2006, at 7:21 AM, Erik Bengtson wrote:
>>
>>     
>>> Hi,
>>>
>>> In case of huge amount of objects loaded /persisted, the flush
>>> method is for
>>> this purpose. I wonder how the cache/state management can be
>>> implemented
>>> without breaking JDO contract and capable to handle load, any tips?
>>>
>>> Thanks
>>>
>>> Erik Bengtson
>>>       
>> Craig Russell
>> Architect, Sun Java Enterprise System http://java.sun.com/products/jdo
>> 408 276-5638 mailto:Craig.Russell@sun.com
>> P.S. A good JDO? O, Gasp!
>>
>>
>>     
>
>
>   

-- 
Michael Bouschen		Tech@Spree Engineering GmbH
mailto:mbo.tech@spree.de	http://www.tech.spree.de/
Tel.:++49/30/235 520-33		Buelowstr. 66			
Fax.:++49/30/2175 2012		D-10783 Berlin

Re: huge volumes and flush

Posted by Erik Bengtson <er...@jpox.org>.

Thanks Craig,

I works now.

Quoting Craig L Russell <Cr...@Sun.COM>:

> Hi Erik,
>
> Generally, use weak references to persistent instances so they can be
> garbage collected when the user no longer holds a strong reference to
> them. Unflushed dirty instances need to be referenced strongly so
> they are not garbage collected. So at flush time, move the flushed
> dirty instances from a strong-reference map to a weak-reference map
> (key = oid, value = weak-reference object).
>
> Craig
>
> On May 24, 2006, at 7:21 AM, Erik Bengtson wrote:
>
> >
> >
> > Hi,
> >
> > In case of huge amount of objects loaded /persisted, the flush
> > method is for
> > this purpose. I wonder how the cache/state management can be
> > implemented
> > without breaking JDO contract and capable to handle load, any tips?
> >
> > Thanks
> >
> > Erik Bengtson
>
> Craig Russell
> Architect, Sun Java Enterprise System http://java.sun.com/products/jdo
> 408 276-5638 mailto:Craig.Russell@sun.com
> P.S. A good JDO? O, Gasp!
>
>

Re: huge volumes and flush

Posted by Craig L Russell <Cr...@Sun.COM>.

Hi Erik,

Generally, use weak references to persistent instances so they can be  
garbage collected when the user no longer holds a strong reference to  
them. Unflushed dirty instances need to be referenced strongly so  
they are not garbage collected. So at flush time, move the flushed  
dirty instances from a strong-reference map to a weak-reference map  
(key = oid, value = weak-reference object).

Craig

On May 24, 2006, at 7:21 AM, Erik Bengtson wrote:

>
>
> Hi,
>
> In case of huge amount of objects loaded /persisted, the flush  
> method is for
> this purpose. I wonder how the cache/state management can be  
> implemented
> without breaking JDO contract and capable to handle load, any tips?
>
> Thanks
>
> Erik Bengtson

Craig Russell
Architect, Sun Java Enterprise System http://java.sun.com/products/jdo
408 276-5638 mailto:Craig.Russell@sun.com
P.S. A good JDO? O, Gasp!