Lionel Cons created AMQ-7232:
--------------------------------
Summary: Incorrect message counters when using virtual destinations
Key: AMQ-7232
URL: https://issues.apache.org/jira/browse/AMQ-7232
Project: ActiveMQ
Issue Type: Bug
Reporter: Lionel Cons
Attachments: Virtual Destinations.jpg
ActiveMQ supports [virtual
destinations|https://activemq.apache.org/virtual-destinations] to magically
link one or more queues to a topic.
It also supports [JMX attributes|https://activemq.apache.org/jmx.html] to count
messages going through the different destinations in a broker. There are both
per-destination attributes ({{EnqueueCount}} and {{DequeueCount}}) and
per-broker attributes ({{TotalEnqueueCount}} and {{TotalDequeueCount}}).
Unfortunately, these two features do not work well together.
Take for instance the following scenario:
* one topic ({{/topic/T}})
* two virtaul queues attached to it({{/queue/Consumer.A.T}} and
{{/queue/Consumer.B.T}})
* one topic producer ({{PT1}})
* two queue consumers on each virtual queue ({{CA1}}, {{CA2}}, {{CB1}} and
{{CB2}})
!Virtual Destinations.jpg!
When sending a single message, we get:
* {{/topic/T}}: {{EnqueueCount += 1}} and {{DequeueCount += 0}}
* {{/queue/Consumer.A.T}}: {{EnqueueCount += 1}} and {{DequeueCount += 1}}
* {{/queue/Consumer.B.T}}: {{EnqueueCount += 1}} and {{DequeueCount += 1}}
* at broker level: {{TotalEnqueueCount += 3}} and {{TotalDequeueCount += 2}}
This is not consistent: when the message leaves the topic to go to the virtual
queues, {{DequeueCount}} (on the topic) does not change while {{EnqueueCount}}
(on the queues) does change.
At broker level, {{TotalEnqueueCount}} gets incremented too much, giving the
impression that 3 messages have been received.
The main question is: should the counters be incremented when a message is
magically forwarded from the topic to the attached virtual queues?
I would argue that these counters should *not* change when messages move
internally (i.e. along dashed lines). This way, we can continue to have
{{TotalEnqueueCount}} being the sum of all {{EnqueueCount}} and at the same
time representing the number of messages received (globally) by the broker.
Idem for {{TotalDequeueCount}} and {{DequeueCount}}.
IMHO, these counters should only change when messages move along solid lines.
If we want to track the internals (i.e. dashed lines) then we should have an
additional counter, a bit like we already have {{ForwardCount}} for network of
brokers.
--
This message was sent by Atlassian JIRA
(v7.6.3#76005)
