[hibernate-issues] [Hibernate-JIRA] Commented: (HHH-3608) DB sequence numbers are not unique when using the pooled SequenceStyleGenerator in multiple JVMs with the same DB

[Strong Liu (JIRA)]

    [ http://opensource.atlassian.com/projects/hibernate/browse/HHH-3608?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=39632#action_39632 ] 

Strong Liu commented on HHH-3608:
---------------------------------

https://issues.jboss.org/browse/JBPAPP-5763
https://issues.jboss.org/browse/JBPAPP-5762

> DB sequence numbers are not unique when using the pooled SequenceStyleGenerator in multiple JVMs with the same DB
> -----------------------------------------------------------------------------------------------------------------
>
>                 Key: HHH-3608
>                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-3608
>             Project: Hibernate Core
>          Issue Type: Bug
>          Components: core
>    Affects Versions: 3.2.6, 3.3.0.GA, 3.3.0.SP1, 3.3.1
>         Environment: Hibernate 3.2.6, Oracle (any version)
>            Reporter: Matthias Gommeringer
>            Assignee: Steve Ebersole
>         Attachments: CustomPooledOptimizer.java, PooledOptimizerTest.java
>
>          Time Spent: 2h
>  Remaining Estimate: 0h
>
> We have several Application Servers (=JVMs) running each of them using Hibernate-Objects with the SequenceStyleGenerator+pooled configured. In unpredictable time intervals it happens that hibernate assigns the same ID to two completely different objects which results in a UniqueConstraintViolation exception from the database. Here an example with a description where hibernate fails:
> DB-Sequence setup:
> start=0
> increment=2
> PooledOptimizer.generate() with 2 threads (first assignment of hiValue/value):
> JVM-1                                                 JVM-2
> value=0=callback.nextval
>                                                             value=2=callback.nextval
> hiValue=4=callback.nextval
>                                                             hiValue=6=callback.nextval
> The problem's cause is in the PooledOptimizer.generate: when it initializes
> the value+hiValue for the first time it invokes callback.nextValue() twice which 
> may provide values that do not belong to each other. The reason is that 
> between the assignment of "value" and "hiValue" another JVM can retrieve a
> DB sequence value from the callback which leads to an inconsistent "value" and "hiValue"
> relation (see example above).
> A fix that works for multiple JVMs would be to invoke the "callback.getNextValue()" maximum once
> per "optimizer.generate()" call:
>     public synchronized Serializable generate(AccessCallback callback) {
>         if ( hiValue < 0 ) {
>             value = callback.getNextValue();
>             hiValue = value + incrementSize;
>         }
>         else if ( value >= hiValue ) {
>             value = callback.getNextValue();
>             hiValue = value + incrementSize;
>         }
>         return make(value++);
>     }
> I attached a testcase that prooves the described problem (you can see that the IDs "2" and "3" are assigned two times).
> I would be very thankful if this problem could be fixed very soon since it is a showstopper which
> occurs very unpredictably.

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