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From "Albert Lee (JIRA)" <j...@apache.org>
Subject [jira] Commented: (OPENJPA-359) OptimisticLockException NOT thrown for entity using Timestamp Version when update from concurrent persistence contexts
Date Mon, 10 Sep 2007 22:28:29 GMT

    [ https://issues.apache.org/jira/browse/OPENJPA-359?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12526286
] 

Albert Lee commented on OPENJPA-359:
------------------------------------

Patrick,

I understand your concern of the proposed changed. 

I'll continue to find other implementation that does not require a synchronized block plus
improving granularity of the version value (time-wise).

Thanks.

> OptimisticLockException NOT thrown for entity using Timestamp Version when update from
concurrent persistence contexts
> ----------------------------------------------------------------------------------------------------------------------
>
>                 Key: OPENJPA-359
>                 URL: https://issues.apache.org/jira/browse/OPENJPA-359
>             Project: OpenJPA
>          Issue Type: Bug
>          Components: jdbc
>    Affects Versions: 1.0.0
>         Environment: WIntel 32 
>            Reporter: Albert Lee
>            Priority: Minor
>         Attachments: OPENJPA-359.patch
>
>
> We ran a test using Timestamp as the version field in an entity, the following (pseudo)
test failed when an OptimisticLockException is expected:
>     em1.persist( e0(pk1) );
>     e1 = em1.find(pk1);
>     e2 = em2.find(pk1);
>     e1.setAttr( "new1");
>     e2.setAttr( "new2");
>     em1.merge( e1 );
>     em2.merge( e2 );    <<<< Expect an OptimisticLockException
> The cause of this problem is because the TimestampVersionStrategy.nextVersion returns
a java.sql.Timestamp(System.currentTimeMillis()); In the Wintel environment, the currentTimeMillis()
only has approximately 15ms resolution. When 2 subsequent Timestamp version objects are requested
within this 15ms interval, both has the same version value. Therefore the em2.merge does not
detected the versions difference between o1 and o2, hence no exception is thrown.
> Due to this behavior, the same test case may failed intermittenly depends on the currentTimeMillis()
resolution and the time when a timestamp version is created.  From some preliminary tests,
the resolution for  wintel, linux and z/os are about 15ms, 2ms and 2ms respectively.
>     

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