project_key: SOA

The MessageSucker is responsible for migrating messages between different members of a cluster, it is a consumer to the remote queue from which it receives messages destined for the queue on the local cluster member.

The onMessage routine, at its most basic, does the following

- bookkeeping for the incoming message, including expiry
- acknowledge the incoming message
- attempt to deliver to the local queue

When the delivery fails, the result is the *appearance* of lost messages.  Those messages which are processed during the failure are not redelivered, but they still exist in the database.

The only way I have found to trigger the redelivery of those messages is to redeploy the queue containing the messages and/or restart that app server.  Obviously neither approach is acceptable.

In order to trigger the error I created a SOA cluster which *only* shared the JMS database, and no other.  I modified the helloworld quickstart to display a counter of messages consumed, clustered the *esb* queue, and then used byteman to trigger the faults.

The byteman rule is as follows, the quickstart will be attached.

RULE throw every fifth send
INTERFACE ProducerDelegate
METHOD send
AT ENTRY
IF callerEquals("MessageSucker.onMessage", true) && (incrementCounter("throwException") % 5 == 0)
DO THROW new IllegalStateException("Deliberate exception")
ENDRULE

This results in an exception being thrown for every fifth message.  Once the delivery has quiesced, examine the JBM_MSG and JBM_MSG_REF tables to see the messages which have not been delivered.

The clusters are ports-default and ports-01, the client seeds the gateway by sending 300 messages to the default.

Adding up the counter from each server *plus* the message count from JBM_MSG results in 300 (or multiples thereof for more executions).