I'm trying to build a custom mq exit to archive messages that hit a queue. I have the following code.
class MyMqExits implements WMQSendExit, WMQReceiveExit{
#Override
public ByteBuffer channelReceiveExit(MQCXP arg0, MQCD arg1, ByteBuffer arg2) {
// TODO Auto-generated method stub
if ( arg2){
def _bytes = arg2.array()
def results = new String(_bytes)
println results;
}
return arg2;
}
...
The content of the message (header/body) is in the byte buffer, along with some unreadable binary information. How can I parse the message (including the body and the queue name) from arg2? We've gone through IBM's documentation, but haven't found an object or anything that makes this easy.
Assuming the following two points:
1) Your sender application has not hard coded the queue name where it puts messages. So you can change the application configuration to send messages to a different object.
2) MessageId of the archived message is not important, only message body is important.
Then one alternative I can think of is to create an Alias queue that resolves to a Topic and use two subscribers to receive messages.
1) Subscriber 1: An administratively defined durable subscriber with a queue provided to receive messages. Provide the same queue name from which your existing consumer application is receiving messages.
2) Subscriber 2: Another administratively defined durable subscriber with queue provided. You can write a simple java application to get messages from this queue and archive.
3) Both subscribers subscribe to the same topic.
Here are steps:
// Create a topic
define topic(ANY.TOPIC) TOPICSTR('/ANY_TOPIC')
// Create an alias queue that points to above created topic
define qalias(QA.APP) target(ANY.TOPIC) targtype(TOPIC)
// Create a queue for your application that does business logic. If one is available already then no need to create.
define ql(Q.BUSLOGIC)
// Create a durable subscription with destination queue as created in previous step.
define sub(SB.BUSLOGIC) topicstr('/ANY_TOPIC') dest(Q.BUSLOGIC)
// Create a queue for application that archives messages.
define ql(Q.ARCHIVE)
// Create another subscription with destination queue as created in previous step.
define sub(SB.ARCHIVE) topicstr('/ANY_TOPIC') dest(Q.ARCHIVE)
Write a simple MQ Java/JMS application to get messages from Q.ARCHIVE and archive messages.
A receive exit is not going to give you the whole message. Send and receive exits operate on the transmission buffers sent/received by channels. These will contain various protocol flows which are not documented because the protocol is not public, and part of those protocol flows will be chunks of the messages broken down to fit into 32Kb chunks.
You don't give enough information in your question for me to know what type of channel you are using, but I'm guessing it's on the client side since you are writing it in Java and that is the only environment where that is applicable.
Writing the exit at the client side, you'll need to be careful you deal with the cases where the message is not successfully put to the target queue, and you'll need to manage syncpoints etc.
If you were using QMgr-QMgr channels, you should use a message exit to capture the MQXR_MSG invocations where the whole message is given to you. If you put any further messages in a channel message exit, the messages you put are included in the channel's Syncpoint and so committed if the original messages were committed.
Since you are using client-QMgr channels, you could look at an API Exit on the QMgr end (currently client side API Exits are only supported for C clients) and catch all the MQPUT calls. This exit would also give you the MQPUT return codes so you could code your exit to look out for, and deal with failed puts.
Of course, writing an exit is a complicated task, so it may be worth finding out if there are any pre-written tools that could do this for you instead of starting from scratch.
I fully agree with Morag & Shashi, wrong approach. There is an open source project called Message Multiplexer (MMX) that will get a message from a queue and output it to one or more queues. Context information is maintained across the message put(s). For more info on MMX go to: http://www.capitalware.com/mmx_overview.html
If you cannot change the source or target queues to insert MMX into the mix then an API Exit may do the trick. Here is a blog posting about message replication via an API Exit: http://www.capitalware.com/rl_blog/?p=3304
This is quite an old question but it's worth replying with an update that's relevant to MQ 9.2.3 or later. There is a new feature called Streaming Queues (see https://www.ibm.com/docs/en/ibm-mq/9.2?topic=scenarios-streaming-queues) and one of the use-cases it is designed to support is putting a copy of every message sent to a given queue, to an alternative queue. Another application can then consume the duplicate messages and archive them separately to the application that is processing the original messages.
Related
I have a Spring boot application (v2.2.10.RELEASE) that subscribes to multiple topics in pubSub and pulls async data and sends it to somewhere else. I am not using SpringGCP, just native google libraries
this is my subscriber setting:
// Instantiate an asynchronous message receiver.
MessageReceiver receiver =
(PubsubMessage message, AckReplyConsumer consumer) -> {
messages.add(message);
consumer.ack();
};
Subscriber subscriber = Subscriber.newBuilder(subscriptionName, receiver)
.setParallelPullCount(2)
.setFlowControlSettings(flowControlSettings)
.setCredentialsProvider(credentialsProvider)
.setExecutorProvider(executorProvider)
//.setChannelProvider()
.build();
With high traffic and big messages (2 - 4 kb) I encounter this info message:
[grpc-default-worker-ELG-1-1] INFO i.grpc.internal.AbstractClientStream - Received data on closed stream
first of all, I don't fully understand what that means? all that I noticed was that when this happens the delivered duplicated messages increase. so I assumed it meant that pubSub tried to reach the subscriber with some messages but the subscriber for some reason was not ready so pubSub will try to deliver the messages again. and hence more duplicates, is that right?
would this problem be solved using the TransportChannelProvider in subscribers? my understanding of the poorly written documentation, that this will create a new channel for delivery when the current in-use channel is closed, hence get rid of the previous log message.
if yes, how do I define the channel target string? and where can I find A NameResolver-compliant URI for the mangagedChannel. the snippet I mean is this:
private TransportChannelProvider getChannelProvider() {
ManagedChannel channel = ManagedChannelBuilder.forTarget(target).usePlaintext(true).build();
return FixedTransportChannelProvider.create(GrpcTransportChannel.create(channel));
}
I am pretty new to GCP so sorry if my question is not coherent enough
Using a custom TransportChannelProvider won't solve this type of issue. This is more likely an issue deeper down in the stack, e.g., at the gRPC level. There have been some open issues for this type of error [1, 2].
With regard to why it is causing duplicates, it is possible that the messages are getting delivered via a stream that is already closed (which aligns with the error message) because they were trapped in a lower-level buffer at the gRPC layer and therefore ended up being duplicates of messages that were subsequently delivered and processed via another stream. This could be a version of the issue discussed in the documentation around large backlogs of small messages. There was a fix for this issue in v1.109.0 of the Java client library, so if you are using a version older than that, it is worth updating.
If duplicates continue to be an issue, it would be best to reach out to support with the name of your subscription and the message IDs of some of the duplicate messages so that they can look at the delivery patterns for those messages and further diagnose if these redeliveries are unexpected.
TLDR; In the context of a topic exchange and queues created on the fly by the consumers, how to have a message redelivered / the producer notified when no consumer consumes the message?
I have the following components:
a main service, producing files. Each file has a certain category (e.g. pictures.profile, pictures.gallery)
a set of workers, consuming files and producing a textual output from them (e.g. the size of the file)
I currently have a single RabbitMQ topic exchange.
The producer sends messages to the exchange with routing_key = file_category.
Each consumer creates a queue and binds the exchange to this queue for a set of routing keys (e.g. pictures.* and videos.trending).
When a consumer has processed a file, it pushes the result in a processing_results queue.
Now - this works properly, but it still has a major issue. Currently, if the publisher sends a message with a routing key that no consumer is bound to, the message will be lost. This is because even if the queue created by the consumers is durable, it is destroyed as soon as the consumer disconnects since it is unique to this consumer.
Consumer code (python):
channel.exchange_declare(exchange=exchange_name, type='topic', durable=True)
result = channel.queue_declare(exclusive = True, durable=True)
queue_name = result.method.queue
topics = [ "pictures.*", "videos.trending" ]
for topic in topics:
channel.queue_bind(exchange=exchange_name, queue=queue_name, routing_key=topic)
channel.basic_consume(my_handler, queue=queue_name)
channel.start_consuming()
Loosing a message in this condition is not acceptable in my use case.
Attempted solution
However, "loosing" a message becomes acceptable if the producer is notified that no consumer received the message (in this case it can just resend it later). I figured out the mandatory field could help, since the specification of AMQP states:
This flag tells the server how to react if the message cannot be routed to a queue. If this flag is set, the server will return an unroutable message with a Return method.
This is indeed working - in the producer, I am able to register a ReturnListener :
rabbitMq.confirmSelect();
rabbitMq.addReturnListener( (int replyCode, String replyText, String exchange, String routingKey, AMQP.BasicProperties properties, byte[] body) -> {
log.info("A message was returned by the broker");
});
rabbitMq.basicPublish(exchangeName, "pictures.profile", true /* mandatory */, MessageProperties.PERSISTENT_TEXT_PLAIN, messageBytes);
This will as expected print A message was returned by the broker if a message is sent with a routing key no consumer is bound to.
Now, I also want to know when the message was correctly received by a consumer. So I tried registering a ConfirmListener as well:
rabbitMq.addConfirmListener(new ConfirmListener() {
void handleAck(long deliveryTag, boolean multiple) throws IOException {
log.info("ACK message {}, multiple = ", deliveryTag, multiple);
}
void handleNack(long deliveryTag, boolean multiple) throws IOException {
log.info("NACK message {}, multiple = ", deliveryTag, multiple);
}
});
The issue here is that the ACK is sent by the broker, not by the consumer itself. So when the producer sends a message with a routing key K:
If a consumer is bound to this routing key, the broker just sends an ACK
Otherwise, the broker sends a basic.return followed by a ACK
Cf the docs:
For unroutable messages, the broker will issue a confirm once the exchange verifies a message won't route to any queue (returns an empty list of queues). If the message is also published as mandatory, the basic.return is sent to the client before basic.ack. The same is true for negative acknowledgements (basic.nack).
So while my problem is theoretically solvable using this, it would make the logic of knowing if a message was correctly consumed very complicated (especially in the context of multi threading, persistence in a database, etc.):
send a message
on receive ACK:
if no basic.return was received for this message
the message was correctly consumed
else
the message wasn't correctly consumed
on receive basic.return
the message wasn't correctly consumed
Possible other solutions
Have a queue for each file category, i.e. the queues pictures_profile, pictures_gallery, etc. Not good since it removes a lot of flexibility for the consumers
Have a "response timeout" logic in the producer. The producer sends a message. It expects an "answer" for this message in the processing_results queue. A solution would be to resend the message if it hasn't been answered to after X seconds. I don't like it though, it would create some additional tricky logic in the producer.
Produce the messages with a TTL of 0, and have the producer listen on a dead-letter exchange. This is the official suggested solution to replace the 'immediate' flag removed in RabbitMQ 3.0 (see paragraph Removal of "immediate" flag). According to the docs of the dead letter exchanges, a dead letter exchange can only be configured per-queue. So it wouldn't work here
[edit] A last solution I see is to have every consumer create a durable queue that isn't destroyed when he disconnects, and have it listen on it. Example: consumer1 creates queue-consumer-1 that is bound to the message of myExchange having a routing key abcd. The issue I foresee is that it implies to find an unique identifier for every consumer application instance (e.g. hostname of the machine it runs on).
I would love to have some inputs on that - thanks!
Related to:
RabbitMQ: persistent message with Topic exchange (not applicable here since queues are created "on the fly")
Make sure the broker holds messages until at least one consumer gets it
RabbitMQ Topic Exchange with persisted queue
[edit] Solution
I ended up implementing something that uses a basic.return, as mentioned earlier. It is actually not so tricky to implement, you just have to make sure that your method producing the messages and the method handling the basic returns are synchronized (or have a shared lock if not in the same class), otherwise you can end up with interleaved execution flows that will mess up your business logic.
I believe that an alternate exchange would be the best fit for your use case for the part regarding the identification of not routed messages.
Whenever an exchange with a configured AE cannot route a message to any queue, it publishes the message to the specified AE instead.
Basically upon creation of the "main" exchange, you configure an alternate exchange for it.
For the referenced alternate exchange, I tend to go with a fanout, then create a queue (notroutedq) binded to it.
This means any message that is not published to at least one of the queues bound to your "main" exchange will end up in the notroutedq
Now regarding your statement:
because even if the queue created by the consumers is durable, it is destroyed as soon as the consumer disconnects since it is unique to this consumer.
Seems that you have configured your queues with auto-delete set to true.
If so, in case of disconnect, as you stated, the queue is destroyed and the messages still present on the queue are lost, case not covered by the alternate exchange configuration.
It's not clear from your use case description whether you'd expect in some cases for a message to end up in more than one queue, seemed more a case of one queue per type of processing expected (while keeping the grouping flexible). If indeed the queue split is related to type of processing, I do not see the benefit of setting the queue with auto-delete, expect maybe not having to do any cleanup maintenance when you want to change the bindings.
Assuming you can go with durable queues, then a dead letter exchange (would again go with fanout) with a binding to a dlq would cover the missing cases.
not routed covered by alternate exchange
correct processing already handled by your processing_result queue
problematic processing or too long to be processed covered by the dead letter exchange, in which case the additional headers added upon dead lettering the message can even help to identify the type of actions to take
We have an application that synchronously reads 4MB messages from an IBM Websphere queue (version 7.5) using JMS. Under certain circumstances, I want to discard messages from the queue without reading them. I am trying to figure out if there is a way to do this programatically without reading the entire 4MB message, which takes several seconds (there could be hundreds of messages that need to be discarded). In the absense of a discard() method (or similar), here is what I have tried:
BytesMessage msg = (BytesMessage)queueReceiver.receiveNoWait();
bytesRead = msg.readBytes(msgBytes, 1024); // just read 1024 bytes
queueReceiver.close();
The above code is no quicker than retrieving the entire 4MB message from the queue (by reading into a larger buffer). This leads me to believe that the receiveNoWait() call is downloading the entire message into an internal buffer before the readBytes() call is made. The only other information I can provide is that the queue is set to "auto acknowledge" when the session is started:
queueSession = queueConnection.createQueueSession(false, QueueSession.AUTO_ACKNOWLEDGE);
If I were to change this to CLIENT_ACKNOWLEDGE and acknowlege the message using msg.acknowledge(), would that have the desired effect? Or is there something I am missing?
Thanks for any help,
Doug
There is no other way, a message must be consumed to take remove it from a queue.
Changing to CLIENT_ACKNOWLEDGE from AUTO_ACKNOWLEDGE will not make any difference as the acknowledge is way to tell the messaging provider to remove a message from queue. The AUTO_ACKNOWLEDGE option tells the JMS client to automatically send a confirmation to provider to remove a message whereas CLIENT_ACKNOWLEDGE is used by the application to explicitly tell the provider to remove message(s).
You could probably take a look at setting an expiry time on messages that you don't plan to consume. Messages with an expiry time set, will not be available for delivery after the expiry time is over. Read through JMSExpiration property of a message.
Given this some more thought and there is potentially one other way here; MQ has the concept of PCF messages - simply this is being able to send an administrative command as a message to a queue manager.
JMS can send these messages - so one open would be to send a CLEAR_QUEUE command when you know you don't want any more messages.
It's quite a broad approach - clearing the entire queue but it depends on what your criteria are for removing messages.
I can see the use case however for selectively removing messages - maybe worth raising a 'request for enhancement' RFE on the IBM developerWorks site?
As far as I know, JMS cannot read part of a message. You can only do that with C or Java (non-JMS).
MQGetMessageOptions gmo = new MQGetMessageOptions();
gmo.options = MQC.MQGMO_NO_WAIT + MQC.MQGMO_FAIL_IF_QUIESCING;
MQMessage getMsg = new MQMessage();
try
{
/* get the message with only 1 byte of message data */
_inQ.get(getMsg, gmo, 1);
}
catch (MQException e)
{
System.err.println(e.getLocalizedMessage() );
}
I have a Java client which monitors RabbitMQ queue. I am able to get the count of messages currently in queue with this code
#Resource
RabbitAdmin rabbitAdmin;
..........
DeclareOk declareOk = rabbitAdmin.getRabbitTemplate().execute(new ChannelCallback<DeclareOk>() {
public DeclareOk doInRabbit(Channel channel) throws Exception {
return channel.queueDeclarePassive("test.pending");
}
});
return declareOk.getMessageCount();
I want to get some more additional details like -
Message body of currently enqueued items.
Total number of messages that was enqueued in the queue since the queue was created.
Is there any way to retrieve these data in Java client?
With AMQP protocol (including RabbitMQ implementation) you can't get such info with 100% guarantee.
The closest number to messages count is messages count returned with queue.declare-ok (AMQP.Queue.DeclareOk in java AMQP client library).
Whilst messages count you receive with queue.declare-ok may match exact messages number enqueues, you can't rely on it as it doesn't count messages which waiting acknowledges or published to queue during transaction but not committed yet.
It really depends what kind of precission do you need.
As to enqueued messages body, you may want to manually extract all messages in queue, view their body and put them back to queue. This is the only way to do what you want.
You can get some information about messages count with Management Plugin, RabbitMQ Management HTTP API and rabbitmqctl util (see list_queues, list_channels).
You can't get total published messages count since queue was created and I think nobody implement such stats while it useless (FYI, with messages flow in average 10k per second you will not even reach uint64 in a few thousand years).
AMQP.Queue.DeclareOk dok = channel.queueDeclare(QUEUE_NAME, true, false, false, queueArgs);
dok.getMessageCount();
To access queue details via http api,
http://public-domain-name:15672/api/queues/%2f/queue_name
To access queue details via command from localhost cli promt,
curl -i -u guest_uname:guest_password http://localhost:15672/api/queues/%2f/queue_name
Where,
%2f is default vhost "/"
I have a publisher that is pushing messages to a topic. I have multiple subscribers each doing a different task once they consume the message from the topic.
Now I want my system to scale to multiple instances of the same process running on different hosts/same host. e.g. I want to run multiple copies of my application A on different hosts so that if one instance of A is slow, then the other instances can pull in subsequent messages and make forward progress..
I found out that this is possible using virtual destinations. I followed the steps here -
http://activemq.apache.org/virtual-destinations.html
But how do i setup my multiple subscribers to the same topic with the same client id? when i try to do that, i get errors. when i try some other way, it doesn't work. can someone help?
Normally, I start a subscriber by doing the below steps -
ActiveMQConnectionFactory connectionFactory = new ActiveMQConnectionFactory(ActiveMQConnection.DEFAULT_USER, ActiveMQConnection.DEFAULT_PASSWORD, ActiveMQConnection.DEFAULT_BROKER_URL;);
activeMQConnection = connectionFactory.createConnection();
activeMQConnection.setClientID("subscriber1");
activeMQConnection.setExceptionListener(exceptionListener);
activeMQSession = activeMQConnection.createSession(false, Session.CLIENT_ACKNOWLEDGE);
activeMQTopic = activeMQSession.createTopic("myTopic");
activeConsumer = activeMQSession.createDurableSubscriber(activeMQTopic, "myTopic");
activeConsumer.setMessageListener(messageListener);
activeMQConnection.start();
when i try to create a 2nd subscriber and pass the topic name as "VirtualTopic.myTopic", nothing happens.
thanks
The virtual topics feature is very simple and quite powerful once you understand it.
When using virtual topics - there is no need for durable consumers. That is because for each client you will get an instance of regular queue created. If you have 5 clients (application A, B, C, D, E) you will get 5 queues created and populated with the copy of the messages every time message is sent to the virtual topic.
Actually it is a limitation of durable consumer - that only ONE connection is allowed per clientId. Being a regular queue, you can create as many consumers as you like and queue will guarantee that 1 message will be received only by 1 consumer. So if you have application A that takes 1 minute to process a message, you can create 5 instances of it listening to the same queue. When you will post 5 messages within 1 second, each of your application will receive its own message to process.
There are not well documented requirements which are not intuitive. To make virtual topic work you need
Use VirtualTopic. in your topic name, for example VirtualTopic.Orders (this prefix can be configured)
Use Consumer. in the name of the queue you. Like Consumer.ApplicationA.VirtualTopic.Orders where ApplicationA is actually your client id
Use regular subscribers not durable ones for the queue above.
Example:
string activeMqConsumerTopic = "Consumer.AmqTestConsumer.VirtualTopic.Orders";
IQueue queue = SessionUtil.GetQueue(session, activeMqConsumerTopic);
IMessageConsumer consumer = session.CreateConsumer(queue);
Queue is created for automatically whenever the first instance of consumer is subscribed to it. Since that moment all messages that are sent to topic are duplicated/copied into all associated queues.
Hope this helps.
Virtual Topics is the answer for you. However you have to define a naming standard for all virtual topic queues. Here is the answer for this:
Virtual Topics helps with following prospective:
1. Load Balancing of messages
2. Fast Failover of Subscriber
3. Re-using same connection Factory for different Producers and Consumers. (Durable Subscribers needs a Unique JMS Client Id and same cannot be reused for any other Producer or consumer)
here is the way to do it, below example creates prefix VTCON.*. So every queue with this prefix and Topic Name at the end will consumer the message.
<virtualDestinations>
<virtualTopic name="TEST.TP01" prefix="VTCON.*." selectorAware="false"/>
</virtualDestinations>
http://workingwithqueues.blogspot.com/2012/05/activemq-virtual-topics-or-virtual.html