Isolation was removed because the vendor community found that
implementing isolation at the component level was too difficult. Some
felt that isolation at the transaction level was the proper solution;
however, no concensus was reached on a specific replacement semantics.
This is a difficult problem that unfortunately has no clear solution at
this time. We will be examining it again in the context of EJB 2.0 and
possible by then a solution will emerge.
At present, EJBs can use JDBC isolation facilities (since databases
differ in the isolation facilities they provide, over reliance on this
can lead to portability problems) as well as any deployment time
isolation control provided by EJB containers. EJB 1.1 does not require
that containers provide any specific isolation control.
The best strategy is to develop EJBs that are as tolerant of isolation
differences as possible. This is the typical technique used by many
optimistic concurrency libraries that have been layered over JDBC and
ODBC.
Ed Roman wrote:
>
> I noticed in the EJB 1.1 specification that declarative isolation levels
> have been removed. I've got some questions about this.
>
> 1) What is the motivation behind removing delcarative isolation? I found it
> to be very useful in EJB 1.0.
>
> 2) If I have a container-managed persistent entity bean, the EJB
> specification says the container will automatically handle isolation. How
> does the container magically know what isolation level to use? Does the
> deployer need to somehow inform the container about the correct isolation
> level to use?
>
> 2.1) If so, how does the deployer know what the correct isolation level
> should be? The deployer may not know anything about the internal
> transactional requirements of the deployed distributed application. How
> should the application assembler communicate isolation requirements to the
> deployer? Isn't this error prone?
>
> 2.2) Doesn't this mean we need to re-specify isolation over and over again
> each time an app is deployed?
>
> --
> Ed Roman
> CEO, The Middleware Company
> Author, "Mastering Enterprise JavaBeans and the Java 2 Platform, Enterprise
> Edition"
> (published by John Wiley & Sons, 1999)
> http://www.middleware-company.com
> [EMAIL PROTECTED]
> 512-346-7994
>
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