Databases Reference
In-Depth Information
This brings us to the
Subscribed Events
dialog where, by clicking on the green plus
sign, we add a new event subscription using the
Event Chooser
dialog introduced in
the section on publishing an event.
Having chosen an event, we can determine how the event is to be delivered using
the
Consistency
option. Transactions are discussed later in
Chapter 15
,
Advanced SOA
Suite Architecture
. The consistency options are:
•
Exactly once by selecting the
one and only one
option. This makes the
event delivery transaction part of the Mediator transaction. If the Mediator
transaction completes successfully, then the event will also be marked as
read, otherwise it will be rolled back and thus appear not to have been
delivered. Transaction boundaries are explained in more detail in
Chapter 15,
Advanced SOA Suite Architecture
At least once by selecting
guaranteed
. This keeps the Mediator transaction
separate from the delivery transaction. The event will be delivered to the
subscriber, but any errors in the Mediator may cause that event to be lost to
that subscriber.
immediate
makes the delivery transaction part of the event publishing
transaction. This option should be avoided as it couples the subscriber and
the publisher.
•
•
Avoid using the
immediate
delivery option as it tightly
couples the publisher to a subscriber that it should be
unaware of. The Java API for this is marked as deprecated,
and it is likely that this option will disappear in the future.
