MessagesKilled on DLQ

Question

I have a DLQ with a large amount of "Messages killed". The broker is a single node. There is no cluster.

According to this documentation "Messages killed" is :

Amount of messages that have been killed on the broker to exceeding the max delivery attempts and is collected form the sum of subcomponent=queues#MessagesKilled for all queues.

What use case is ActiveMQ Artemis trying to solve? Why on earth does DLQ have any amount of Messages killed? I expect this value to be 0 initially anyway.

Attributes:

• Acknowledge attempts 68890
• Address DLA
• Configuration managed false
• Consumer count 0
• Consumers before dispatch 0
• Dead letter address DLA
• Delay before dispatch -1
• Delivering count 0
• Delivering size 0
• Durable true
• Durable delivering count 0
• Durable delivering size 0
• Durable message count 1539
• Durable persistent size 2183288
• Durable scheduled count 0
• Durable scheduled size 0
• Enabled true
• Exclusive false
• Expiry address ExpiryQueue
• ...
• Group buckets -1
• Group count 0
• Group first key
• Group rebalance false
• Group rebalance pause dispatch false
• Id 1006063
• Last value false
• Last value key
• Max consumers -1
• Message count 1539
• Messages acknowledged 0
• Messages added 70429
• Messages expired 0
• Messages killed 68890
• Name jms.queue.satellitanalys_request.DLQ
• Object Name org.apache.activemq.artemis:broker="0.0.0.0",component=addresses,address="DLA",subcomponent=queues,routing-type="multicast",queue="jms.queue.satellitanalys_request.DLQ"
• Paused false
• Persistent size 2183288
• Prepared transaction message count 0
• Purge on no consumers false
• Retroactive resource false
• Ring size -1
• Routing type MULTICAST
• Scheduled count 0
• Scheduled size 0
• Temporary false
• User

Answer 1

The actual description of "Messages killed" can be acquired from the MBean itself which states:

number of messages removed from this queue since it was created due to exceeding the max delivery attempts

Generally speaking, the use-case being solved here is a message which cannot be consumed (for whatever reason) is being removed from the queue (i.e. killed) so that the consumer can receive, and hopefully successfully process, a different message. The behavior is 100% configurable in broker.xml.

There are a handful of important metrics here:

• Acknowledge attempts 68890
• Message count 1539
• Messages acknowledged 0
• Messages added 70429
• Messages killed 68890

Acknowledge "attempts" and actual acknowledgements are tracked independently because, for example, a message may be acknowledged in a transaction and then that transaction can be rolled back in which case the message won't actually be acknowledged. That appears to be the case here since there have been 68,890 attempts to acknowledge but 0 actual acknowledgements. I can only assume that the max-delivery-attempts for this queue is 1 since there are also 68,890 killed messages. Notice too that the number of messages added is 70,429 which corresponds to the message count of 1,539 (i.e. 70,429 - 68,890 = 1,539). Everything seems to be accounted for.

My conclusion is that you have (or had) a consumer that is (or was) attempting to consume messages from this queue via a transaction, and that transaction was rolled back in every instance.

Keep in mind that a "dead-letter queue" is just a normal queue like any other. All the same configuration and semantics apply to it as they would apply to any other queue.