Re: [eclipselink-users] Best practices for clearing the entity manager

[Tom Ware <tom.ware@xxxxxxxxxx>]

Hi John,

  Anything that is managed in an EntityManager will be cached in that 
EntityManager (i.e. the results of query.getResultList())

  EclipseLink has another level of caching, and if you want to avoid that, the 
best bet is to turn off shared caching.  Info about how to turn that off here 
(you can do it in annotations or persistence unit properties):

http://wiki.eclipse.org/Using_EclipseLink_JPA_Extensions_%28ELUG%29#Using_EclipseLink_JPA_Extensions_for_Entity_Caching

  If it is just an issue with query results, simply use the eclipselink.refresh 
query hint and set it to true.

-Tom


John Ament wrote:
> Tom,
>
> No, I realize that the results of a find are cached, and this is 
> expected.  What I am getting concerned with is that I have no cache 
> configuration in my app, yet the results of a Query.getResultList are 
> getting cached, which I don't expect.  Is there a way to force these to 
> not cache at all?
>
> Thanks,
>
> John
>
> On Wed, Feb 24, 2010 at 9:06 AM, Tom Ware <tom.ware@xxxxxxxxxx 
> <mailto:tom.ware@xxxxxxxxxx>> wrote:
>
>     Hi John,
>
>      What do you mean when you say caching is not enabled?  What
>     settings are you using to disable the cache? Note that within an
>     open entity manager there will always be a cache of the objects that
>     are managed within that entity manager.
>
>      Rarely does disabling the cache actually achieve what you want it
>     to since the cache is also used to maintain identity.  There are a
>     number of options you can use to fine tune your cache and/or force
>     queries to the database.
>
>      Take a look at the following link for some caching options.  Some
>     things that might be good to try are using a CacheType of WEAK,
>     setting the cache to not be shared, and having it expire after a
>     certain amount of time.
>
>     http://wiki.eclipse.org/Using_EclipseLink_JPA_Extensions_%28ELUG%29#Using_EclipseLink_JPA_Extensions_for_Entity_Caching
>
>      Also have a look at our query hints.  You could specify the
>     eclipselink.cache-usage hint to tell a query to avoid the cache or
>     the eclipselink.refresh hint to tell the query to refresh from the
>     database.
>
>     http://wiki.eclipse.org/Using_EclipseLink_JPA_Extensions_%28ELUG%29#How_to_Use_EclipseLink_JPA_Query_Hints
>
>      There is also the entityManager.refresh() operation that forces
>     objects to be refreshed and the entityManager.clear() operation that
>     cleans our the individual entityManager.
>
>     -Tom
>
>
>     John Ament wrote:
>
>         Hey everyone
>
>         So I've begun to notice that there's some odd behavior in
>         eclipse link when it comes to a multiple server environment
>         that's not cluster (e.g. 4 instances of glassfish running on 2
>         servers).  Basically, it looks like repeated calls to em.find as
>         well as execution of queries returns the same data rather than
>         actually running the queries against the database.  Does anyone
>         have any tips on how to avoid issues like this?  Caching is not
>         enabled.
>
>         Thanks,
>
>         John
>
>
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