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http://opensource.atlassian.com/projects/hibernate/browse/HHH-3608?page=c...
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Steve Ebersole commented on HHH-3608:
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{quote}
Also I have studied some JBoss logs that suggest that optimizers are not just created
during startup of the server. From what I have seen optimizers are can also be created
after some error resulting in an exception. Now I could be wrong about this so please
verify yourself, but if so this means that the current code is riskier that one might
first think particularity in i clustered environment.
{quote}
Bjorn, the optimizer is created when the generator it is part of is
"configured". That process happens once per generator instance. The double
call happens the first time the pooled optimizer is used, which is the first time the
generator is called. Unless the error somehow rebuilds the SessionFactory I don't see
how what you say happens happens.
DB sequence numbers are not unique when using the pooled
SequenceStyleGenerator in multiple JVMs with the same DB
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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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