> From: A mailing list for Enterprise JavaBeans development
> [mailto:[EMAIL PROTECTED]]On Behalf Of Sacha Labourey
> The problem then with MDB is that as multiple MDB may be activated to read
> the messages from the same queue, we loose the just guaranteed sequence
This is not quite true. Some clarifications:
- While the EJB 2.0 specification mentions the possibility for the container to
activate several instances to process messages in parallel, this is not a
requirement.
- Regardless, EJB 2.0 containers will most likely implement parallel processing of
messages. In such a case, MDB's will typically have their onMessage() methods
called in the same order as if they had been invoked by JMS directly. The
difference is in the emission of receipts: depending on how long the onMessage()
methods take to complete, they might not emit their receipts in the same order as
the messages were received.
> (and
> it is not possible to tell the EJB server to serialize the calls for a
> particular queue (not in a standard way I mean) in order to conserve our
> sequence ordering.)
Actually, nothing prevents the container from reading a proprietary flag letting
it know what kind of processing the bean provider wishes. Sometimes, ordering of
messages will be more important than multiplexing.
--
Cedric
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