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http://opensource.atlassian.com/projects/hibernate/browse/HHH-3608?page=c...
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Michael Berkowitz commented on HHH-3608:
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I have applied Adrian Shum's fix and tested it pretty thouroughly (I ran 25
simultaneous servlets that each added records to two different tables that share the same
sequence-number generator; beforehand it consistently gave me conflicts, now i've run
it many times with nary a glitch)
I hope I'm not out of line in saying that I would have thought a simple fix like this
would have made its way into trunk code by now. Does it havesome insidious bug that
hasn't yet been mentioned here?
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: 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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