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Re: [eclipselink-users] non-repeatable read in combination with a delete 
James, 

Thanks for your reply.

>Your removeCompany code is wrong.  Before removing an object you must
>remove
>any references to it.  Normally you would get a constraint error, but
you
>have the constraint defined in the other direction.
The removeCompany code is normally executed in a different thread after
all employees are removed. Furthermore in the testcase there are no
employees when the removeCompany code is executed. Could you explain
which references you are referring to?

>If you are concerned about concurrency, then you should also be using
>optimistic version locking.  This would allow the  version of the
company >to be checked so that it knows it is an existing object.
What I want and what I expected was that both testcases would give the
same constraint error. In the actual application code optimistic locking
is used but has no effect on the fact that there is a different outcome
depending on when the registerObject of the Company is executed.
How would version checking help for a deleted Object?

>This is also related to your usage of registerObject instead of
>registerExistingObject and your does-exist policy.  The default does
exist
>is to check the cache, as it assumes the cache is correct.  But your
remove
>has corrupted the cache, you could set another type of existence check
if
>you intend to corrupt your cache.
registerExistingObject seems relevant. Both testcases give the same
constraint error when using registerExistingObject. This is what I want
and excpted. However I do not yet understand how the remove has
corrupted the cache. Could you please explain?

Greetings,
Huub Sepers


-----Original Message-----
From: eclipselink-users-bounces@xxxxxxxxxxx
[mailto:eclipselink-users-bounces@xxxxxxxxxxx] On Behalf Of James
Sutherland
Sent: Wednesday, January 19, 2011 3:15 PM
To: eclipselink-users@xxxxxxxxxxx
Subject: Re: [eclipselink-users] non-repeatable read in combination with
a delete


Your removeCompany code is wrong.  Before removing an object you must
remove
any references to it.  Normally you would get a constraint error, but
you
have the constraint defined in the other direction.

If you are concerned about concurrency, then you should also be using
optimistic version locking.  This would allow the  version of the
company to
be checked so that it knows it is an existing object.

This is also related to your usage of registerObject instead of
registerExistingObject and your does-exist policy.  The default does
exist
is to check the cache, as it assumes the cache is correct.  But your
remove
has corrupted the cache, you could set another type of existence check
if
you intend to corrupt your cache.


Huub Sepers-2 wrote:
> 
> Hi,
> 
>  
> 
> I have a question about a non-repeatable read scenario whereby a
parent
> entity is deleted.
> 
>  
> 
> See the enclosed testcase.
> 
>  
> 
> The following scenario:
> 
>  
> 
> We have 2 entities with a parent-child relationship, Company-Employee.
> Suppose the parent is removed in one thread wile another thread
inserts
> a child for the same parent.
> It appears that different things happen according to timing issues.
> 
>  
> 
> It appears that when the parent is removed (commit) just after it has
> been found but just before it is registered then the parent will be
> inserted as a new object with the same primary key.
> 
> See testcase "testWR".
> 
> When the parent is removed after it has been registered an ORA-02291
> (parent key not found) will occur.
> 
> See testcase "testWR2"
> 
>  
> 
> The testcases are single threaded but illustrate the point.
> 
>  
> 
> I have tested this with Eclipselink 1.1.4, 1.1.2, 1.1.1 and 1.2.0.
> 
>  
> 
> Questions:
> 
> I would expect the ORA-02291 to occur in both cases?
> 
> What can I do to get a consistent error in both cases?
> 
>  
> 
> Met vriendelijke groet,
> 
> Huub Sepers
> 
> Software Engineer
> 
> 
> 


-----
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Sutherland 
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