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From Aristedes Maniatis <>
Subject Re: 3.0 cache documentation
Date Thu, 07 May 2009 13:14:00 GMT

On 04/05/2009, at 8:33 PM, Andrus Adamchik wrote:

> I tried to stay away from the implementation details and give a user  
> perspective instead. If there is still a feeling that the docs are  
> lacking in this area, please share your thoughts. I will try to  
> address any reasonable suggestions.

OK. I have some questions which may need a little more explanation in  
the docs.

On the object cache page you discuss Memory Management with the shared  
and local caches.

1. Should this section be moved to the parent page since it applies  
both to query and object caches? That is, is the memory space of  
10,000 shared between object and query cache?

2. If an object is stored in the shared cache by one context and  
another context uses it, will localObject() need to be called on it to  
move it to the correct context or is that all handled automatically?

3. If objects are always synchronised between local caches is  
refreshing ONLY needed when thinking about multiple instances of the  
application in separate JVMs? If so, this could be made even clearer  
in the refreshing section.

"Object caching happens behind the scenes, so the only case when users  
need to worry about object cache is when an object gets stale and  
needs to get refreshed"

maybe instead:

"Object cache refreshing is done automatically for you be Cayenne, so  
the only case users need to worry about refreshing manually is when  
you are running multiple instances of the application in separate  
JVMs. In that case you have the following options:"

4. I'd like to understand a little better the relationship between  
query cache and object cache. For example, will Cayenne every perform  
a query against the database and then throw away the results it gets  
because it sees that the objectIds are already in the object cache?  
That is, does a query which hits the db always result in a refresh of  
the object cache?

And, if the query is cached and therefore no SELECT is issued, will  
the results sometimes include hollow objects which will then be  
faulted? Perhaps the object cache was full and those objects had been  

So, whether the object cache is refreshed will depend on whether a  
query hits the db or comes from cache?


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