Hello everyone,
there's a serious bug inside EclipseLink's sequence pre-allocation,
assigning
the same id on more than one entity.
Imagine an entity TestEntity with allocationSize = 2 on its
SequenceGenerator annotation.
Please have a look at following Test case snippet:
//make sure that JPA entity has a allocationSize of 2
TestEntity obj1 = new TestEntity();
//em is our EclipseLink entity manager
em.persist(obj1);
TestEntity obj2 = new TestEntity();
em.persist(obj2);
TestEntity obj3 = new TestEntity();
em.persist(obj3);
assertFalse(obj1.getId().equals(obj2.getId()));
//this one failes:
assertFalse(obj2.getId().equals(obj3.getId()));
As you can see, the EntityManager assigns the same id twice:
register_new_for_persist, TestEntity[TEST_ENTITY_ID=null]
execute_query, ValueReadQuery(sql="SELECT TEST_ENTITY_ID.NEXTVAL FROM
DUAL")
reconnecting_to_external_connection_pool
SELECT TEST_ENTITY_ID.NEXTVAL FROM DUAL
sequencing_preallocation, TEST_ENTITY_ID, 2, 5446377, 5446378
assign_sequence, 5446377, TestEntity[TEST_ENTITY_ID=null]
register_new_for_persist, TestEntity[TEST_ENTITY_ID=null]
assign_sequence, 5446378, TestEntity[TEST_ENTITY_ID=null]
register_new_for_persist, TestEntity[TEST_ENTITY_ID=null]
execute_query, ValueReadQuery(sql="SELECT TEST_ENTITY_ID.NEXTVAL FROM
DUAL")
reconnecting_to_external_connection_pool
SELECT TEST_ENTITY_ID.NEXTVAL FROM DUAL
sequencing_preallocation, TEST_ENTITY_ID, 2, 5446378, 5446379
assign_sequence, 5446378, TestEntity[TEST_ENTITY_ID=null]
What makes this bug even more critical:
Someone may expect that the commit will fail on commit-time at the
latest, throwing a unique contraint violation on the primary key. But
this is not the case, interestingly.
In fact, this bug confuses the EclipseLink change tracking
mechanism in a way that it cannot determine the changes correctly.
Some changes, which are made to the entity after calling persist(), but
before commit()/flush() may not been tracked correctly, hence not
written.
This bug happens at least in EclipseLink 1.1.2.
The only workaround for this bug seems to be to set allocationSize=1 on
all JPA entities,
which, of course, may affect performance.
Best regards,
Patric
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