I am not able to clear the connection queue in Nifi. The only change i made to the PutJMS processor was to change the URL to failover:(address)?randomize=false. The message just stopped in the queue and did not proceed to PutJMS. I stopped all the processors after sometime in the hope that I will change the config again for further testing. But since the queue is not empty and it is not allowing me to change the config in PutJMS processor.
PS: I am trying to send messages to IBM MQ using PutJMS.
If you would like to investigate this further, you can get a NiFi thread dump and look for the "putJMS" related threads to see what those threads are waiting on.
# ./nifi.sh dump <dump-file-name>
Unfortunately right now there is no way to interrupt/kill these threads from within NiFi's UI. NiFi will be adding that ability in a future release. For now, as Saikrishna mentioned, a NiFi restart will be required to kill these threads if they never complete on their own.