Crucial question about Toplink Essentials JPA in OC4J 10.1.3.3

Question

Hi all!
I'm developing an EJB 3.0 service which will be deployed to an OracleAS 10.1.3.3 and even after I've read lots of docs and articles, I still got an unanswered question:
I know JPA leaves concurrent data access to the application's responsibility (or the vendor implementation's), that Oracle explicitly recommends using @Version to enable JPA's standard optimistic locking and also that Toplink Essentials JPA is OC4J's default persistence provider for EJB 3.0 modules. Considering this last important fact, what will be the default locking mode assumed by Toplink Essentials if I don't use @Version?
Looking at Toplink Essentials JPA extensions doc preview for OC4J 11g (http://www.oracle.com/technology/products/ias/toplink/jpa/resources/toplink-jpa-extensions.html), I found that I can use @OptimisticLocking to define the locking policy when defining an entity and use a lock type that doesn't require me to define a @Version field. But that annotation doesn't exist in version 10.1.3.3. Is there another way to define locking policy and type (on global or per entity basis) in version 10.1.3.3?
Any help will be really welcome!
TIA,
Eduardo.

Answer 1

Quoting Mr. Doug Clarke:
"Eduardo,
The only way to ensure that concurrent writers to the database don't overwrite one another is to either lock optimistically or pessimistically (i.e.: SELECT ... FOR UPDATE). Both of these approaches are supported by Oracle TopLink as well as TopLink Essentials. If neither is used then no locking is applied and the last writer will succeed leaving the database in a potentially corrupted state. Also note that minimal writes are used so each thread only updates the columns it changes so the resulting state of the database could be a combination of the two concurrent writes. Users of JPA are strongly recommended to use optimistic locking to ensure concurrent writing scenarios do not produce unexpected result in their database.
Our JPA implementation in 10.1.3.3 is TopLink Essentials which is the Open Source references implementation of JPA derived from Oracle TopLink developed in GlassFish. This edition of TopLink only has support for JPA's @Version annotation as you noted. This approach does require a dedicated column in the database table for comparison on write to detect changes made since this thread's version of the original data was read.
In Oracle TopLink 11g we have implemented JPA 1.0 in our product. This means that full capabilities of TopLink are available through JPA along with some custom annotations to assist in configuring them. This includes the additional optimistic locking policies provided for schemas where adding version columns is not possible. These capabilities are not included in TopLink Essentials. Customers can access these capabilities in the 11gR1 technology previews as well as in the new Eclipse Persistence Services Project "EclipseLink" which is the full functionality of Oracle TopLink developed as an open source solution. Oracle TopLink 11g and its distribution of EclipseLink are not yet available in a supported release."