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From Craig L Russell <Craig.Russ...@Sun.COM>
Subject Re: Object Locking and Application Server (container-managed) environment
Date Wed, 26 Sep 2007 15:54:42 GMT
Hi Kevin,

The transaction model for Kodo is based on the pretty well documented  
JDO specification which includes both optimistic and datastore  
transaction semantics. To this model were added the explicit locking  
APIs which complicate things just a bit. But reading the JDO spec  
might be a good start to understand how Kodo worked and therefore how  
OpenJPA's underpinnings work. Ducking now in case there have been  
massive changes to OpenJPA to remove these architecture features...

Craig

On Sep 26, 2007, at 6:00 AM, Kevin Sutter wrote:

> Discovered a useful openjpa property...
>
> On 9/25/07, Kevin Sutter <kwsutter@gmail.com> wrote:
>>
>> Hi,
>> I'm trying to figure out the ins and outs of Section 3 Object  
>> Locking as
>> they relate to running OpenJPA within an application server
>> (container-managed) environment such as WebSphere.  It seems that  
>> several of
>> these properties and/or API's are assuming an application-managed
>> environment outside of a container.  Either that, or there are  
>> implied
>> behaviors of the container environment that WebSphere is not  
>> providing.
>>
>> For example, the ReadLockLevel property allows for none, read, or  
>> write
>> values.  What does it mean for "none" in an application server  
>> environment?
>> If the Container has already initiated a global (JTA) transaction,  
>> when
>> OpenJPA requests a Connection (via the <jta-data-source> element),  
>> this
>> Connection is automatically enlisted in the Transaction.  Thus,  
>> when the
>> "Select..." statement is issued, we will get a Read Lock on the  
>> row with the
>> default isolation level setting (supposed to be Read Committed).   
>> So, how is
>> OpenJPA supposed to honor the "none" ReadLockLevel request?
>>
>> Several places in this section of the document, there are  
>> references to
>> optimistic and non-optimistic (pessimistic) transactions.  Not lock
>> managers, but transactions.  The OpenJPA manual indicates that it can
>> support optimistic transactions by not issuing the database  
>> transaction
>> until flush or commit time.  But, I don't see how we are can  
>> configure for
>> the use of optimistic vs pessimistic transactions.  It looks like the
>> EntityTransaction interface is optimistic by default.  But, is  
>> there anyway
>> to control the optimisticity (new word) of a global transaction?   
>> The answer
>> to these questions actually help with the first example outlined  
>> above.
>
>
> Okay.  It was pointed out to me that the openjpa.Optimistic  
> property exists
> to indicate whether to use optimistic or non-optimistic transaction
> semantics.  So, it's not just an implicit operation.  But, I guess my
> question still exists on how this applies to container managed JTA
> transactions.  I will continue to investigate, but if there are any  
> existing
> experts in this area, I'd appreciate some insights.  :-)  Thanks!
>
> Many other similar questions are in my mind, but let's start with  
> these
>> since I think these will give a basis for the rest of the discussion.
>>
>> Thanks,
>> Kevin
>>

Craig Russell
Architect, Sun Java Enterprise System http://java.sun.com/products/jdo
408 276-5638 mailto:Craig.Russell@sun.com
P.S. A good JDO? O, Gasp!


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