We have observed the following behavior of RabbitMQ and are trying to understand if it is correct and how to resolve it.
Scenario:
A (persistent) message is delivered into a durable queue
The (single) Consumer (Spring-AMQP) takes the message and starts processing => Message goes from READY to UNACK
Now the broker is shut down => Client correctly reports "Channel shutdown"
The consumer finishes the processing, but can not acknowledge the message as the broker is still down
Broker is started again => Client reconnects
As a result, one message remains unack'ed forever (or until the client is restarted).
Side note: In the Rabbit Admin UI, I can see that two channels are existing now. The "dead" one that was created before the broker restart, containing the unacked message and a new one that is healthy.
Is this behavior expected to be like that? It seems to me "correct" in the way, that RabbitMQ can not know after the broker restart, whether the message processing was completed or not. But what solution would exist than to get that unacked message back into the queue and to heal the system without restarting the consumer process?
The RabbitMQ team monitors this mailing list and only sometimes answers questions on StackOverflow.
Is this behavior expected to be like that? It seems to me "correct" in the way, that RabbitMQ can not know after the broker restart, whether the message processing was completed or not.
Yes, you are observing expected behavior. RabbitMQ will re-enqueue the message once it determines that the consumer is really dead. Since your consumer re-connects with what must be the same consumer tag as before, it is up to that process to ack or nack the message.
Related
After the rabbitmq server or cluster is restarted, all the queue have recover all the message even the messages have be acked (from the point that rabbitmq server is started), and process all messages again.
Queue details
From my understanding, setting persistenet to false in the message arguments, the message will not survive if broker restart. Also, I have set durabele to false for the queue.
Did I missed any other settings?
Making a message persistent true is fine as you do not want to loose message in case of rabbitmq restart. Secondly, it is also fine to make the queue durable so that you dont want to loose the queue in case of rabbitmq restart. I will suggest please check the message consumer code as it looks like it is not commiting the transaction on its side making the message available on the queue. What you can do is after consuming messages please stop the consumer and check on the RabbitMQ if the messages are still available on the queue. If the messages are still available on queue after stopping the consumer , then there must be some issue on the consumer code.
Using web-stomp with RabbitMQ and web-socket (SockJS not used), after sending a message to a queue, how can the consumer be notified by the broker or monitor that the sent message has been consumed?
I've experimented with subscribing to the queue which makes the client a consumer and the goal is not to receive the message for processing, but to know when a consumer elsewhere has picked up, acknowledged the message and is no longer in the queue.
In retrospect, I really do believe I'm breaking the spirit of "send it and forget it" with this question's approach.
The better approach will be to subscribe to another queue that will receive the "finished processing" message that will be sent from the processor. The client can take the appropriate actions from there.
I have a 3 node cluster of Rabbitmq behind a HAproxy Load Balancer. When I shut down a node, Rabbitmq successfully switches the queue to the other nodes. However, I notice that Logstash stops pulling messages from the queue unless I restart it. Is this a problem with the way rabbitmq operates? i.e. it deactivates all active consumers. I am not sure if log stash has any retry capability. Anyone run into this issue?
Quoting rabbit mq documentation, page for clustering first
What is Replicated? All data/state required for the operation of a
RabbitMQ broker is replicated across all nodes. An exception to this
are message queues, which by default reside on one node, though they
are visible and reachable from all nodes.
and high availability
Clients that are consuming from a mirrored queue may wish to know that
the queue from which they have been consuming has failed over. When a
mirrored queue fails over, knowledge of which messages have been sent
to which consumer is lost, and therefore all unacknowledged messages
are redelivered with the redelivered flag set. Consumers may wish to
know this is going to happen.
If so, they can consume with the argument x-cancel-on-ha-failover set
to true. Their consuming will then be cancelled on failover and a
consumer cancellation notification sent. It is then the consumer's
responsibility to reissue basic.consume to start consuming again.
So, what does all this mean:
You have to mirror queues
The consumers should use manual ACK
The consumers should reconnect on their own
So the answer to your question is no, it's not a problem with rabbitmq, that's simply how it works. It's up to clients to reconnect.
I've got some trouble understanding the confirm of RabbitMQ, I see the following explanation from RabbitMQ:
Notes
The broker loses persistent messages if it crashes before said
messages are written to disk. Under certain conditions, this causes
the broker to behave in surprising ways. For instance, consider this
scenario:
a client publishes a persistent message to a durable queue
a client consumes the message from the queue (noting that the message is persistent and the queue durable), but doesn't yet ack it,
the broker dies and is restarted, and
the client reconnects and starts consuming messages.
At this point, the client could reasonably assume that the message
will be delivered again. This is not the case: the restart has caused
the broker to lose the message. In order to guarantee persistence, a
client should use confirms. If the publisher's channel had been in
confirm mode, the publisher would not have received an ack for the
lost message (since the consumer hadn't ack'd it and it hadn't been
written to disk).
Then I am using this http://hg.rabbitmq.com/rabbitmq-java-client/file/default/test/src/com/rabbitmq/examples/ConfirmDontLoseMessages.java to do some basic test and verify the confirm, but get some weird results:
The waitForConfirmsOrDie method doesn't block the producer, which is different from my expectation, I suppose the waitForConfirmsOrDie will block the producer until all the messages have been ack'd or one of them is nack'd.
I remove the channel.confirmSelect() and channel.waitForConfirmsOrDie() from publisher, and change the consumer from auto ack to manual ack, I publish all messages to the queue and consume messages one by one, then I stop the rabbitmq server during the consuming process, what I expect now is the left messages will be lost after the rabbitmq server is restarted, because the channel is not in confirm mode, but I still see all other messages in the queue after the server restart.
Since I am new to RabbitMQ, can anyone tells me where is my problem of the confirm understanding?
My understanding is that "Channel Confirmation" is for Broker confirms it successfully got the message from producer, regardless of consumer ack this message or not. Depending on the queue type and message deliver mode, see http://www.rabbitmq.com/confirms.html for details,
the messages are confirmed when:
it decides a message will not be routed to queues
(if the mandatory flag is set then the basic.return is sent first) or
a transient message has reached all its queues (and mirrors) or
a persistent message has reached all its queues (and mirrors) and been persisted to disk (and fsynced) or
a persistent message has been consumed (and if necessary acknowledged) from all its queues
Old question but oh well..
I publish all messages to the queue and consume messages one by one, then I stop the rabbitmq server during the consuming process, what I expect now is the left messages will be lost after the rabbitmq server is restarted, because the channel is not in confirm mode, but I still see all other messages in the queue after the server restart.
This is actually how it should work, IF the persistence is enabled. If the server crashes or something else goes wrong, the messages cannot be confirmed, and thus, won't be removed from the queue.
Messages will only be removed from the queue if they are confirmed to be handled, or the broker didn't yet write it to memory or disk before the server crashed.
Confirming and acknowledging can be set off if wanted, and the producer won't be waiting for the acks. I cannot find the exact command for it right now, but it does exist.
More on the acks and confirms: https://www.rabbitmq.com/reliability.html
Was running a system that uses multiple msmq's on the same machine, ran fine for about a day then I get the error about Insufficient resources when trying to post a message to one of the queues. Investigated via this blog post:
http://blogs.msdn.com/b/johnbreakwell/archive/2006/09/18/761035.aspx
I don't see anything in there about investigating the dead-letter queue.
Looked at the queues, realized the only queue that had any messages left in it was the transactional dead-letter queue, purged it, now the app(s) run again and can post messages to private queues.
I guess my main question is explain to me the trans dead-letter queue and how I can manage it.
thanks.
There will be nothing in the blog about the Dead Letter Queue as it is just a queue, like any other.
You have messages in the DLQ because you have enabled Negative Source Journaling in your application. An error condition has meant the original messages have died and ended up in the DLQ, as requested by your application. Ideally, if you are using the DLQ, you have a separate thread looking for messages in it.
You should have monitoring enabled on the total number of messages in the server so that you get an early alert when messages start piling up somewhere unexpectedly.
Cheers
John Breakwell
Ran into this issue today with our MSMQ/NServiceBus setup. From what I understand, manual queue purges will move messages to the Transaction Dead Messages queue. Clearing this queue out resolved the problem for us.