6:52 a.m.
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http://opensource.atlassian.com/projects/hibernate/browse/HHH-3608?page=c...
]
Björn Hamrin commented on HHH-3608:
-----------------------------------
I've had similar problems with duplicate primary keys from an Oracle sequence. I agree
that the problem is the two consecutive calls to callback.getNextValue() and the
assumption that no other thread or VM manages to call callback.getNextValue() in between.
The other odd thing about the two calls to callback.getNextValue() in the generate()
function in PooledOptimizer is that always leaves an extra large gap in the sequence when
a server starts up, as noted by errorken (part 3). The solution proposed by Adrian Shum is
to use callback.getNextValue() as the bottom value instead of the top value. That should
certainly work but changes the behavior. I would simply propose that one always set the
value to hiValue - incrementSize, when callback.getNextValue() has been called. The only
time callback.getNextValue() needs to be called twice is when a sequence is completely
new, since it is likely to return 1 the very first time. I would would propose a change of
the generate() to the following:
public Serializable generate(AccessCallback callback) {
if ( hiValue < 0 ) {
hiValue = callback.getNextValue();
if ( hiValue <= incrementSize )
hiValue = callback.getNextValue();
value = hiValue - incrementSize;
}
else if ( value >= hiValue ) {
hiValue = callback.getNextValue();
value = hiValue - incrementSize;
}
return make( value++ );
}
I have tested this by plugging in a custom optimizer and running some tests. It appears to
work. If anyone can see problem with this solution I would appreciate feedback.
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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