On 7/19/06, nlif <[EMAIL PROTECTED]> wrote:
Hi,
I am using ActiveMQ's MessageGroups feature in order to send and receive
several related messages as a single unit-of-work. I am using a transacted
producer, so all messages are sent atomically, but I don't know how to
implement the consumer.
Its actually the session which is transacted; which then implies the
producers and consumers created on the transacted session take part in
the same transaction.
The way I see it - the consumer should accumulate
the messages until it has all of them and then construct the aggregate, save
it and only then - acknowledge them.
Just to clarfiy, the problem I am trying to solve is that of the consumer
crashing after acknowleding some, but not all, of the messages in the group.
This will result in loss of messages.
If you want to consume several messages in a transaction, its
sometimes easiest to just use a consumer, pull all the messages out,
aggregate them and send them using JMS - as you are kinda doing a
custom 'transaction batch' using your own business logic to decide the
batch size.
e.g.
session = connection.createSession(true, 0);
consumer = session.createConsumer(destination);
while (true) {
m1 = consumer.receive();
...
mn = consumer.receive();
producer.send(someAggregationMessage);
session.commit();
}
So I started-off with a MessageListener configured with Jencks, for pooling.
The MessageListener should collect all messages in the group, and once it
has all of them - it should acknowledge all of the together. Now, ensuring
all messages are indeed delivered to the same MessageListener is taken care
of by the MessageGroups feature. But since Jencks commits the transaction
when the onMessage() method returns - this prevents me from acknowledging
all messages together.
Yeah. Am wondering if we could add some custom batching plugin into
the Resource Adapter in ActiveMQ maybe - its a little tricky though
I know some people throw a RuntimeException in the onMessage() method in
order to make Jencks rollback, but that's awkward to say the least, since it
will cause messages I already have to be redlivered again and again!
Yeah - if you are doing this kind of batch processing, you either have
to go with the whole batch being redelivered again - or you catch
errors and send bad messages to dead letter queues.
Furthermore, if I am not mistaken, although all Jencks' threads share the
same MessageListener instance, each message is (or may be) delivered by a
different session. This means, that even if I did find a way to commit the
transaction myself - it would still not achieve the behavior I need.
Yes - Jencks generally load balances messages across sessions; though
the batching feature in the ActiveMQResourceAdapter does AFAIK use the
same session for 1 batch.
--
James
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http://radio.weblogs.com/0112098/
