To prepare for a system resource becoming unavailable or
a problem message, configure the system to stop the message-driven
bean (MDB) or Service Component Architecture (SCA) composite automatically.
To maintain message ordering, do not use an exception destination.
Before you begin
This task assumes that you have deployed an enterprise application
containing a message-driven bean (MDB), or a business-level application
containing a Service Component Architecture (SCA) composite, that
interacts with external system resources.
The destination to which
the MDB or SCA composite listens must not use an exception destination,
that is, the exception destination for the queue or topic space destination
must be configured as none.
To complete this task, you need
the following information:
The JCA MBean emits JMX notifications to indicate that
the MDB or SCA composite is paused, and that the MDB or SCA composite
has resumed. Consider registering a message listener on the JCA MBean
to receive the JMX notifications.
About this task
In this scenario, the enterprise application is a continuously
running system that uses a deployed MDB or SCA composite to access
an external system resource.
When a problem message (msg1 in
this scenario) is encountered, it is put back on the queue.
Instead
of msg1 being made available to the MDB or SCA composite immediately,
it is hidden for the Delay between failing message retries retry
delay (five seconds in this scenario).
When the number of hidden
messages reaches the Sequential failed message threshold,
the MDB or SCA composite will not process any further messages until
one of the hidden messages becomes re-available. In this scenario,
this threshold is reached as soon as msg1 is hidden.
When the Delay between failing message retries for
msg1 expires, msg1 is unhidden and reprocessed.
This process
is repeated until msg1 reaches its Maximum failed deliveries per message limit
(five times in this scenario).
After msg1 is unhidden for the
fourth time, rolled back and rehidden, the Sequential failed message threshold is
reached and the MDB or SCA composite stops automatically. A JMX notification
is emitted by the JCA MBean and a log entry alerts the system administrator
that the MDB has stopped.
Procedure
- Navigate to the deployed enterprise application that contains
the MDB or SCA composite.
- From the MDB or SCA composite, navigate to its JMS activation
specification. Click .
- Enter a value of 1 for the Sequential failed message threshold.
- Enter a value of 5000 for the Delay between failing message retries.
- Save the configuration.
- Navigate to the destination to which the MDB or SCA composite
is listening. Click one of the following paths, as appropriate:
- Under Exception destination,
select None.
- Enter a value of 5 in Maximum failed deliveries per message.
- Save your changes to the master configuration.
- When you receive a JMX notification and a log entry indicating
that the MDB or SCA composite (or endpoint) has been paused, investigate
the problem with the system resource that the MDB or SCA composite
was using. While the MDB or SCA composite is paused,
because no exception destination is configured, msg1 remains on the
queue. No other messages are processed.
- If you resume the MDB or SCA composite but the problem
with the failing message continues, the maximum failed deliveries
limit is reached on the first retry of the message, but because no
exception destination is configured, the message is not moved to another
queue. Instead, the whole queue point is blocked to all consumers
for the Delay between failing message retries retry
delay interval (five seconds in this scenario). After this time, consumers
begin again. If the failing message is still there, and fails again,
the queue point is blocked for another 5 seconds. This process continues
until you remove the failing message from the queue, either by deleting
it manually or solving the problem with it, and in doing so allowing
the consuming application to succeed in processing.
- Log on to the administrative console again, navigate to
the same enterprise application and click Resume on
the administrative panel for the MDB or SCA composite. You can also
resume the MDB or SCA composite by using scripting and the JCA MBean.
The initial JMX notification and log entry indicate which MBean to
use to resume the MDB or SCA composite. The MDB or
SCA composite begins to be driven with the messages that are on the
destination.
Results
You have configured the system to protect itself from external
resource failures while maintaining message ordering.
What to do next
When the MDB or SCA composite is resumed, the JCA MBean
emits a JMX notification to indicate that the MDB or SCA composite
has resumed. Messages on the queue are consumed, messages that had
failed are retried, and the transaction commits.