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

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Thanks Craig,

I works now.

Quoting Craig L Russell <Craig.Russell@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:
> 
>
> 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!
>
>

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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 <Craig.Russell@Sun.COM>:
>
> 
>
>
>


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Michael Bouschen		Tech@Spree Engineering GmbH
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