The core feature would be to have a fixed size queue (fixed in the number of unacked messages). Once this limit was reached, new publications would result in the oldest message being dropped. In addition a further option would prevent the replacement of oldest by newest message when a client was processing the messages. Publication would fail in this state.
The objective of the second option above is to prevent 'gaps' appearing in the sequence seen by the consuming client.
otherwise the ring queue is expected to have the same basic features as a regular queue (such as acquire modes, transactional delivery, ability to cluster, transient vs durable, etc)
There are two 'policy types' through which these features are delivered, these and the desired limits, are passed as name-value pairs in the arguments parameter to the queue.declare command used to create the queue. qpid.policy_type=ring will cause the queue to delete the oldest message when an enqueue would otherwise breach the configured queue limit. qpid.policy_type=ring_strict does the same, but if the oldest message has been delivered to a client but not yet acknowledged, it will not be removed to make way for new messages and the attempted enqueue will result in a failure. The limit is set through either qpid.max_size (the total size of all messages on the queue) or qpid.max_count (the number of messages on the queue). The functionality is covered by the QueuePolicyTests suite in Qpid, particularly the testRingPolicy and testStrictRingPolicy test cases. Test strategy: Case 1: 1.1. configure a queue with qpid.policy_type=ring, qpid.count=5 1.2. publish 10 distinct messages 1.3. read the messages from the queue and verify that only the last five were delivered Case 2: As for case 1, but using qpid.policy_type=ring_strict in step 1 Case 3: 1. configure a queue with qpid.policy_type=ring_strict, qpid.count=5 2. publish 5 messages 3. subscribe to queue and receive but do not ack all 5 messages 4. attempt to publish a further message which should fail Case 4: 1. configure a queue with qpid.policy_type=ring_strict, qpid.count=5 2. publish 5 messages 3. subscribe to queue and receive but do not ack all 5 messages 4. attempt to publish a further message which should succeed 5. ack all messages
Wrote test program in Python (cvs:/cvs/dist/tests/distribution/MRG_Messaging/qpid_test_ring_queue_bz441700/) Test result show that ring queues are implemented according to expectations comment#3 ... One remark regarding test case 4 (D), the description is wrong - the policy type should be 'ring' and not 'ring_strict'. This is checked with Gordon. Test result: $ ./bz441700.py ----> TEST-A - Policy: ring - Ring size: 5 - Using queue name: ringq_testA_ring_5 Sending: ring test A ... message 1/10 Sending: ring test A ... message 2/10 Sending: ring test A ... message 3/10 Sending: ring test A ... message 4/10 Sending: ring test A ... message 5/10 Sending: ring test A ... message 6/10 Sending: ring test A ... message 7/10 Sending: ring test A ... message 8/10 Sending: ring test A ... message 9/10 Sending: ring test A ... message 10/10 Received: ring test A ... message 6/10 Received: ring test A ... message 7/10 Received: ring test A ... message 8/10 Received: ring test A ... message 9/10 Received: ring test A ... message 10/10 Message queue is empty Got the expected number of messages ====> TEST-A - PASS ----> TEST-B - Policy: ring_strict - Ring size: 5 - Using queue name: ringq_testB_ring_strict_5 Sending: ring test B ... message 1/10 Sending: ring test B ... message 2/10 Sending: ring test B ... message 3/10 Sending: ring test B ... message 4/10 Sending: ring test B ... message 5/10 Sending: ring test B ... message 6/10 Sending: ring test B ... message 7/10 Sending: ring test B ... message 8/10 Sending: ring test B ... message 9/10 Sending: ring test B ... message 10/10 Received: ring test B ... message 6/10 Received: ring test B ... message 7/10 Received: ring test B ... message 8/10 Received: ring test B ... message 9/10 Received: ring test B ... message 10/10 Message queue is empty Got the expected number of messages ====> TEST-B - PASS ----> TEST-C - Policy: ring_strict - Ring size: 5 - Using queue name: ringq_testC_ring_strict_5 Sending: ring test C.1 ... message 1/5 Sending: ring test C.1 ... message 2/5 Sending: ring test C.1 ... message 3/5 Sending: ring test C.1 ... message 4/5 Sending: ring test C.1 ... message 5/5 ----> Receiving 5 messages, acking 2 Received: ring test C.1 ... message 1/5 ** Message acked Received: ring test C.1 ... message 2/5 ** Message acked Received: ring test C.1 ... message 3/5 Received: ring test C.1 ... message 4/5 Received: ring test C.1 ... message 5/5 Message queue is empty Got the expected number of messages ----> Sending 5 new messages Sending: ring test C.2 ... message 1/5 Sending: ring test C.2 ... message 2/5 Sending: ring test C.2 ... message 3/5 ERROR: Could not send messages ====> Sending 5 new messages, failed as expected -- TEST-C PASS ----> TEST-D - Policy: ring - Ring size: 5 - Using queue name: ringq_testD_ring_5 Sending: ring test D.1 ... message 1/5 Sending: ring test D.1 ... message 2/5 Sending: ring test D.1 ... message 3/5 Sending: ring test D.1 ... message 4/5 Sending: ring test D.1 ... message 5/5 ----> Receiving 5 messages, acking 2 Received: ring test D.1 ... message 1/5 ** Message acked Received: ring test D.1 ... message 2/5 ** Message acked Received: ring test D.1 ... message 3/5 Received: ring test D.1 ... message 4/5 Received: ring test D.1 ... message 5/5 Message queue is empty Got the expected number of messages ----> Sending 5 new messages Sending: ring test D.2 ... message 1/5 Sending: ring test D.2 ... message 2/5 Sending: ring test D.2 ... message 3/5 Sending: ring test D.2 ... message 4/5 Sending: ring test D.2 ... message 5/5 ====> Sent 5 messages - TEST-D PASS SUMMARY: Score: 0 (0 = no errors) Overall result: PASS
An advisory has been issued which should help the problem described in this bug report. This report is therefore being closed with a resolution of ERRATA. For more information on therefore solution and/or where to find the updated files, please follow the link below. You may reopen this bug report if the solution does not work for you. http://rhn.redhat.com/errata/RHEA-2009-0035.html