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http://opensource.atlassian.com/projects/hibernate/browse/HHH-3608?page=c...
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Drew Davidson commented on HHH-3608:
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Steve, I don't think Ryan was being rude at all - he was being descriptively correct
in saying "fundamentally broken" as the code has issues in the fundamental
assumptions about the two calls to the sequence's nextValue. You seem very defensive
about this, and stating your credentials is pointless - everyone can make misassumptions
or mistakes.
I think that the fact that this code is demonstrably misbehaving, as seen by multiple
independent sources, should at least make you question the fundamentals and assumptions of
the code. Perhaps you should acknowledge this instead of stubbornly refusing to see that
there is a problem or lecturing others on how much you know and they don't know.
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
Priority: Blocker
Attachments: CustomPooledOptimizer.java, 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.
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