Re: [eclipselink-users] Read/write and caching

[Christopher Delahunt <christopher.delahunt@xxxxxxxxxx>]

Hello,

The doc at
http://wiki.eclipse.org/EclipseLink/Examples/JPA/Caching
describes caching options in EclipseLink, but the first paragraph 
briefly states that EntityManagers have their own cache.
What you are hitting is that each EntityManager has its own cache 
separate from the shared cache you have configured.  Once an entity is 
loaded into one, it keeps them isolated from seeing changes made in the 
other EntityManagers, making them act like a transaction.

You should either release the EntityManager and obtain a new one on each 
loop, or clear the EntityManager so that entities will be pulled from 
the database or shared cache.

Best Regards,
Chris

On 15/03/2012 2:57 AM, Sebastian Weber wrote:
> Hi All,
>
> …and post again. I have some trouble with my Mail-Server and
> subcribe/notification/confirm messages from the mailing list.
>
> I hope you see this post fort he first time. Thanks in advance for you help!
>
>
> I still like to setup a simple EclipseLink example with MySQL Database
> and EclipseLink Caching. I found enough information about how I can
> configure the cache but my Example still not working.
>
> My Example:
> Entry DBTSIRS:
> @Entity
> @Cache(
> type=CacheType.FULL,
> size=200,
> expiry=10000
> )
> @NamedQueries({
> @NamedQuery(name = "getAllIRS",
> query = "SELECT e FROM DBTSIRS e",
> hints = {@QueryHint(name = QueryHints.CACHE_USAGE,
> value = CacheUsage.CheckCacheThenDatabase)})
> })
> public class DBTSIRS implements Serializable {
>
> /** */
> private static final long serialVersionUID = 3937702217098914083L;
>
> @Id
> private int irsID;
>
>
>
> @Column(columnDefinition = "VARCHAR(50)")
> private String gpslongitude;
>
> @Column(columnDefinition = "VARCHAR(50)")
> private String gpslatitude;
> …
> }
>
> Thread 1 Just read from DB and print:
> List<DBTSIRS> irs2 = this.em.createQuery("SELECT r from DBTSIRS r WHERE
> r.irsID = 1",
> DBTSIRS.class).setHint(QueryHints.CACHE_USAGE,CacheUsage.CheckCacheByPrimaryKey).getResultList();
>
> List<DBTSIRS> irs3 = this.em.createNamedQuery("getAllIRS",
> DBTSIRS.class).getResultList();
>
> Thread 2 change the position attributes in DBTSIRS:
> this.em.getTransaction().begin();
> DBTSIRS dbirs = this.em.find(DBTSIRS.class, 1);
> int lng = Integer.parseInt(dbirs.getGpslongitude());
> int lat = Integer.parseInt(dbirs.getGpslatitude());
> dbirs.setGpslatitude(Integer.toString(++lat));
> dbirs.setGpslongitude(Integer.toString(++lng));
> this.em.merge(dbirs);
> this.em.getTransaction().commit();
>
> So these two Threats are running each 5 seconds. Each Thread ha a
> separate EntityManager generated by the EntityManagerFactory. Thread 2
> is modifying the attributes. By the way String will not be the best data
> type to store position information! Yes I know! Just for this test!
> After the Commit the position attributes the DB show me the current
> valid position information (1,2,3,4,…)
> The Thread 1 still print me the first read value (1).
>
> I guess I do something wrong on the caching configuration. The
> modification don’t affect to the EntityManager cache of Thread 1.
>
>
> Can you give me a hint where I can find information about this “issue”
> or better what I doing wrong.
>
>
> Thanks a lot!
>
> Sebastian
>
> --
> Freundliche Grüße / Best Regards
>
> Sebastian Weber
>
> ----------------------------------------------------------------------------------------------
>
> Sebastian Weber, M.Sc.
> Kommunikationssysteme / Communication Systems
> Fakultät für Ingenieurwissenschaften / School of Engineering
> Hochschule für Technik und Wirtschaft des Saarlandes (HTW) /
> University of Applied Sciences
>
> Standort / Location:
> HTW Hochschul-Technologie-Zentrum (HTZ)
> Campus IT-Park (CIP)
> Altenkesseler Strasse 17/D2
> 66115 Saarbruecken, Germany
>
> Phone: +49 681 5867-663
> Mobile: n.a.
> Fax: +49 681 5867-671
> E-Mail: sebastian.weber@xxxxxxxxxxxxxxx
> URL: http://www.htw-saarland.de
>
> ----------------------------------------------------------------------------------------------
>
>
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