Ah, the joys of quoting out of context and out of date. We will
update our FAQ appropriately. The below quote is a version of
something I wrote discussing our Alpha product back in the fall
of 1998. At that time, the only relevant EJB containers on the
market were WebLogic and WebSphere, and I was referring to those
product. The fact is that now, a year and a half later, some
other EJB containers do support multiplexed dispatching for parallel
transactions.
However, I will contend that supporting this feature requires running
on something functionally equivalent to a POA. Yes, you can build a
POA-like infrastructure on top on a BOA (I have) but it is messy and
quite complicated (at least mine was). It is in fact just about as
hard as implementing the POA altogether (again, something I have
been involved with).
The basic problem is that simpler dispatching models assume that the
object key is sufficient to locate the server-side object. In EJB,
for entity beans, to implement optimistic concurrency, you need to
dispatch on both the object key and the transaction id. Which can
be complicated because you may not know what is the current transaction
until you look at its deployment descriptor (the entity could be running
in the callers transaction, or could be running in a new transaction)
which requires knowing what the object is going to be.
Again, this is what the POA is designed to support. Building it from
scratch is non-trivial. This is "why [many] other EJB containers [still
do not] provide this functionality", even today.
-jkw
Evan Ireland wrote:
>
> "Louth, William (Exchange)" wrote:
> >
> > Hi Robert,
> >
> > In the inprise documentation they do elaborate on this association a bit
> > more:
> >
> > Sidebar:
> > Implementing this parallel transaction feature is non-trivial for most EJB
> > container vendors, because it requires a relatively sophisticated
> > server-side object dispatch model. What is required is the ability to
> > dispatch on a server-side object using both the primary key (which is
> > usually embedded in the object reference) and the current transaction. Doing
> > this multi-key dispatch is very hard to implement on top of an RMI or BOA
> > style server-side model, which is why no other EJB container provides this
> > functionality. We leverage the POA, which is a server- side frame-work which
> > is much more sophisticated, and which is much more conducive to implementing
> > this functionality.
>
> The Inprise technical writers would be well-advised not to make unsubstantiated
> claims about "other EJB" containers. They are wrong.
> ________________________________________________________________________________
>
> Evan Ireland Sybase EAServer Engineering [EMAIL PROTECTED]
> Wellington, New Zealand +64 4 934-5856
>
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