I use ActiveMQ resource adapter and JBoss EAP 6.3 to integrate with ActiveMQ broker running inside JBoss A-MQ container. I have a MDB deployed in EAP and it consumes messages from the ActiveMQ broker. The MDB is also configured to use a thread pool of maximum 20 threads to increase performance.

After applied R2P6 patch on JBoss A-MQ 6.1 and deployed resource adapter "activemq-rar-5.9.0.redhat-611442.rar" from the patch R2P6 to JBoss EAP 6.3, the performance of MDB was significantly decreased and it was working just like a single-threaded:

19:25:53,466 INFO [class org.jboss.fuse.qa.amq.rar.mdb.TestMDBean] (default-threads - 10) Message: 0 sent at: Wed Jul 15 19:25:53 IST 2015
19:25:54,477 INFO [class org.jboss.fuse.qa.amq.rar.mdb.TestMDBean] (default-threads - 40) Message: 19 sent at: Wed Jul 15 19:25:53 IST 2015
19:25:55,482 INFO [class org.jboss.fuse.qa.amq.rar.mdb.TestMDBean] (default-threads - 39) Message: 18 sent at: Wed Jul 15 19:25:53 IST 2015
19:25:56,487 INFO [class org.jboss.fuse.qa.amq.rar.mdb.TestMDBean] (default-threads - 38) Message: 17 sent at: Wed Jul 15 19:25:53 IST 2015
19:25:57,492 INFO [class org.jboss.fuse.qa.amq.rar.mdb.TestMDBean] (default-threads - 37) Message: 16 sent at: Wed Jul 15 19:25:53 IST 2015
19:25:58,497 INFO [class org.jboss.fuse.qa.amq.rar.mdb.TestMDBean] (default-threads - 36) Message: 15 sent at: Wed Jul 15 19:25:53 IST 2015
...

But after I replaced the resource adapter with the one from R2P4 patch "activemq-rar-5.9.0.redhat-611431.rar", the problem just disappeared. It was truly working like multi-threaded again.