On 28 Mar 2008, at 09:42, Ramit Arora wrote:
Hi All,
I have a situation where I have to consume persisent messages from
many
non-durable subscribers. My publishers push persistent messages to a
topic,
which are consumed asynchronously by non-durable subscribers. I am
using the
AMQ Persistence Adapter & CLIENT_ACKNOWLEDGE. If I kill a non-durable
subscriber & bring it up again, some messages are lost, which is
expected.
But consider the following case:
1. Start a publisher publishing persistent messages to a topic.
2. Start a non-durable subscriber which is slow compared to the
publisher.
3. Kill the broker when 100 messages have been published but only 50
have
been consumed.
4. Since the publisher & subscriber are failover clients, they wait
for the
broker to come up again.
5. Restart the broker.
6. Try to get the remaining 50 messages to the non-durable subscriber.
Step 6 does not work in both 5.0 & the latest 5.1 snapshot.
Shouldn't the
remaining 50 messages be delivered? The JMS spec says:
"A JMS provider must deliver a PERSISTENT message once-and-only-
once. This
means a JMS provider failure must not cause it to be lost, and it
must not
deliver it twice. PERSISTENT (once-and-only-once) and NON_PERSISTENT
(at-most-once)
message delivery are a way for a JMS client to select between delivery
techniques that may lose a messages if a JMS provider dies and those
which
take extra effort to insure that messages can survive such a
failure. There
is
typically a performance/reliability trade-off implied by this
choice. When a
client selects the NON_PERSISTENT delivery mode, it is indicating
that it
values performance over reliability; a selection of PERSISTENT
reverses the
requested trade-off."
Queues donot suffer from this problem. Please let me know if I am
missing
something.
Thanks,
Ramit
--
View this message in context:
http://www.nabble.com/Consuming-persistent-messages-from-a-non-durable-subscriber-tp16348721s2354p16348721.html
Sent from the ActiveMQ - User mailing list archive at Nabble.com.
Message delivery by default is persistent - but there is a fundamental
difference in the contract between queues and topics:
Queue messages are always persisted
Topic messages are persisted if there exists a durable subscriber for
that topic.
You can get around this by using virtual destinations - see here:
http://activemq.apache.org/virtual-destinations.html
cheers,
Rob
