Is there a way to configure a JMS message queue to drop all received messages automatically? (In other words: for the sender it must look like the message arrived ok, but the queue should silently drop it. That is, the queue should behave like "/dev/null") In case that matters, I'm most interested in IBM MQ, however, if JMS specification offers this possibility, that would be even better.
Since I already tried searching, and did not find such a possibility, I suspect the answer is "no". So an answer that confirms that this is the case (and I'm not missing anything) is also valid for me.
Use case: test a system, that sends messages to a real JMS queue, which (in the test setup) are not read out by any other program. (I do not want to mock the JMS queue, to keep the test environment as close to production as possible. For the same reason, it is also not a valid solution to e.g. set "time to live" for the messages on the client side.)
How about making a queue which you put to being an alias to a topic with noone listening on it?
e.g.:
def qalias(MYQUEUE) target(DUMMYTOPIC) targtype(TOPIC)
def topic(DUMMYTOPIC) topicstr(DUMMYTOPIC)
Then you can put to the queue, it becomes a publish and if noone is listening on the queue it vanishes. amqsput MYQUEUE QM for example will work fine.
When you want to then consume the messages, change the QALIAS to either point to a real queue, or replace the QALIAS definition with a QLOCAL for example.
The only downside is if anyone is subscribed to every topic, but for testing purposes you can
If you want a different approach where you can control (turn off/on) the flow of messages being deleted/removed, then an MQ Service and my 'emtyq' program is another option.
Here's a write up I did a while ago on the subject: http://www.capitalware.com/rl_blog/?p=3680
Related
I created a SpringBoot/Spring AMQP project where I configured a listener on a RabbitMQ queue. Question: Is there any way to leave the message in the queue? Let me explain: I consume the message and do some things (eg save on db), if something goes wrong I would like to be able to reconsume the message.
Thanks in advance
You need to think about configuring your listener container with transactions, so when DB call fails, the transaction is going to be rolled back and an AMQP message will not be acked on RabbitMQ.
See docs for more info: https://docs.spring.io/spring-amqp/docs/current/reference/html/#transactions
I don't know about the "Spring" way of accomplishing this, but what you describe is the normal behavior for AMQP consumers that do not automatically acknowledge.
From the documentation:
In automatic acknowledgement mode, a message is considered to be successfully delivered immediately after it is sent.
When you turn off automatic acknowledgment, your consumer must explicitly acknowledge the message, otherwise it will not be dequeued (or as you put it, it will be left "in the queue"). You will then need to simply ACK the message at the very end of your operation, when you are certain that your operation succeeded (and perhaps coordinated with your database transaction).
There is always the question of what to do first; acknowledge first or commit your database transaction first? Without adding complexity, you must choose what's best depending on what failure mode is less problematic for you, i.e. Would you rather tolerate a duplicated message or a missing message?
Is it possible to keep a history of messages (with message content would be perfect) that have already been retrieved and are no longer on a queue?
In the application I can see when the sender attempts to put the message in the queue and when the receiver attempts to pick the messages up, but I'd like to see when the message really arrived into the queue and when the messages were really received.
Does MQ Explorer have this function? How would I use it?
What you are looking for is a message tracking/auditing software for IBM MQ. You can find a list of what is available here.
It is possible to use an API exit to make copies of messages in a queue or to audit both PUT and GET operations.
It is also possible to put messages to a topic, then create as many administrative subscriptions to destination queues as required. Something can then GET and log messages from one of those destination queues. The problem with this is that MQ changes the message ID between publication and consumption whereas in a queue it remains static.
There is no native MQ function to capture messages. It's possible to use linear logs and later scrape the logs but these do not necessarily capture all messages due to optimization. (A message PUT to a waiting getter outside of syncpoint for example.) However there is at least one commercial product to scrape linear transaction logs to audit message activity.
The philosophy of MQ in general is that it is the delivery mechanism and deals with envelope data to route and deliver but does not deal with payload data. WAS, IIB and other broker/transformation engines are where IBM has put all of the functions that deal with message payloads.
I am working with someone who is trying to achieve a load-balancing behavior using JMS Queues with IBM Websphere MQ. As such, they have multiple Camel JMS consumers configured to read from the same Queue. Despite that this behavior is undefined according to the JMS spec (last time I looked anyway), they expect a sort of round-robin / load-balancing behavior. And, while the spec leaves this undefined, I'm led to believe that the normal behavior of Websphere MQ is to deliver the message to only one of the consumers, and that it may do some type of load-balancing. See here, for example: When multi MessageConsumer connect to same queue(Websphere MQ),how to load balance message-consumer?
But in this particular case, it appears that both consumers are receiving the same message.
Can anyone who is more of an expert with Websphere MQ shed any light on this? Is there any situation where this behavior is expected? Is there any configuration change that can alleviate this?
I'm leaning towards telling everyone here to use the native Websphere MQ clustering facility and go away from having multiple consumers pointing at the same Queue, but that will be a big change for them, so I'd love to discover a way to make this work.
Not that I'm a fan of relying on anything that's undefined, but if they're willing to rely on IBM specific behavior, I'll leave that up to them.
The only way for them to both receive the same messages are:
There are multiple copies of the message.
The apps are browsing the message without a lock, then circling back to delete it.
The apps are backing out a transaction and making the message available again.
The connection is severed before the app acknowledges the message.
Having multiple apps compete for messages in a queue is a recommended practice. If one app goes down the queue is still served. In a cluster this is crucial because the cluster will continue to direct messages to the un-served queue instance until it fills up.
If it's a Dev system, install SupportPac MA0W and tell it to trace just that one queue and you will be able to see exactly what is happening.
See the JMS spec in section 4.4. The provider must never deliver a second copy of an acknowledged message. Exception is made for session handling in 4.4.13 which I cover in #4 above. That's pretty unambiguous and part of the official spec so not an IBM-specific behavior.
I’m writing a server/client game, a typical scenario looks like this: one client (clientA) send a message to the server, there is a MessageDrivenBean in server to handle such messages. After the MDB finished its job, it sends the result message back to another client (clientB).
In my opinion I only need two queues for such communication, one for input the other for output. Creating new queue for each connection is not a good idea, right?
The Input queue is relative clear, if more clients are sending message at the same time, the messages are just waiting in the queue, while there are more MDB instances in server, that should not a big performance issue.
But on the other side I am not quite clear about the output queue, should I use a topic instead of a queue? Every client is listening the output queue, one of them gets the new message and checks the property to determine if the message is to it, if not, it rollback the transaction, the message goes back to queue and be ready for other client … It should work but must be very slow. If I use topic instead, every client gets a copy of the message, if it’s not to it, just ignores the message. It should be better, right?
I’m new about message system. Is there any suggestion about my implementation? Thanks!
To begin with, choosing JMS as a gaming platform is, well, unusual — businesses use JMS brokers for delivery reliability and transaction support. Do you really need this heavy lifiting in a game? Shouldn't you resort to your own HTTP-based protocol, for example?
That said, two queues are a standard pattern for point-to-point communication. Creating a queue for a new connection is definitely not OK — message-driven beans are attached to queues at deployment time, so you won't be able to respond to queue creation events. Besides, queues are not meant to be created and destroyed in short cycles, they're rather designed to be long-living entities. If you need to deliver a message to one precise client, have the client listen on the server response queue with a message selector set to filter only the messages intended for this client (see javax.jms.Message API).
With topics it's exactly as you noted — each connected client will get a copy of the message — so again, it's not a good pattern to send to n clients a message that has to be discarded by n-1 clients.
MaDa;
You could stick one output queue (or topic) and simply tag the message with a header that identifies the intended client. Then, clients can listen on the queue/topic using a selector. Hopefully your JMS implementation has efficient server-side listener evaluation.
Im a web developer ended up in some j2ee development (newbie). I sincerely need this theory confirmed.
I been given the privilege to deliver a message from our system (producer) to the SOA Enterprice service bus (consumer) when the user hits the save button. The information can not be missed or not delivered and the delivery order must be kept.
Environment:
Jboss eap 5.1 as the producer.
JNDI server is the ESB (maybe standard).
Jboss ESB as the consumer.
My weapon of choice is JMS, p2p, due to the asynchronous nature.
When the producer is abut to send the message some problems can occur:
ESB is down causing JNDI exception
Queue manager is for some reason not awake or wrongly configured. This should cause some JMS exception.
Network hickup, causing a JMS error.
So Im looking for some failover pattern. Here is my suggestion:
Add a internal JMS queue to which the message is initially added.
Add a MDB that listen to the internal queue and tries to send it to the target queue (ESB).
If failing in any way log fatal and send email to cool support people.
This should generate a reliable pattern where a message remains on the internal que until processed by the MDB.
Please advice.
Best Regards
ds
Well a 'temporary' queue is not a totally bad idea, but during the time from moving data from one queue to putting it on another you'll have a potential window of risk. Even though that window is close to nothing, what would happen if you got some failure right there and then? -You'd have to put the message back on the queue (and there you'd get into the problem with getting it in the correct order - nasty stuff!) or hold on to it in some way until you put it the other queue (which in turn can be cumbersome if you'd e g get into some failure-situaton.
A more stable solution would be to put data in a db with a queue-order column. You can then select your data in the correct order, send it to the new queue, and finally flag it as 'done' or something or even (better?) remove the data in the db.