[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

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 Priority: Blocker Attachments: PooledOptimizerTest.java 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.