I'm new to ActiveMQ and trying to find anything that explicitly outlines how JMSMessageID behaves with durable subscribers and selectors, however, I am struggling to find much.
As an example: JMSType = 'car' AND color = 'blue' AND weight > 2500 as a selector. Each subscriber will only receive messages from the topic where the criteria match. When each receives said messages are the JSMMessageID unique for each subscriber or are they unique for the entire topic before it was filtered by the selector for the subscriber.
If not is there a way that I can get the JSMessageID to be unique for each subscriber so that it can be used as a form of sequence number using custom messageID layout: 1, 2, 3... ad infinitum.
The Message ID is set by the producer at the time of send, the broker passes along a copy of the message to each Topic subscription (durable or not) with the message ID that it was sent with. You cannot alter the ID the broker uses that value to track the message and ensure that it is preserved until each subscription that it was dispatched to or stored for has acknowledged it.
Related
I am trying to make an SSE Spring application, using Webflux. According to the documentation, the message is not sent to the sink if there is no subscriber. In my use case, I would like that the subscriber would receive the last message when calling for subscription. I have found that Sink can be configured in following way:
Sinks.many().replay().latest();
And when I have both publisher and subscriber, and the next subscriber calls for subscription, he receives the last sent message, which is great. However if I don't have any subscribers, publisher sends the message and then first subscriber comes in, it receives none. Which is just as documentation above says actually, but I am thinking how to solve that issue to meet my needs. As a workaround I did something like this:
if (shareSinks.currentSubscriberCount() == 0) {
shareSinks.asFlux().subscribe();
}
shareSinks.tryEmitNext(shareDTO);
But subscribing the publisher to its own subscription doesn't sound like a clean way to do this...
This is a matter of hot and cold publishers. Currently, your publisher (Sinks.many().replay().latest()) is a cold publisher. Events that are being emitted while there is no subscriber, will just vanish.
What you need is a so called hot publisher. Hot publishers cache the events and a new subscriber will receive all previously cached events.
This will do the trick:
final Sinks.Many<String> shareSinks = Sinks.many()
.replay()
.all(); // or .limit(10); to keep only the last 10 emissions
final Flux<String> hotPublisher = shareSinks.asFlux()
.cache(); // .cache() turns the cold flux into a
// hot flux
shareSinks.tryEmitNext("1");
shareSinks.tryEmitNext("2");
shareSinks.tryEmitNext("3");
shareSinks.tryEmitNext("4");
hotPublisher.subscribe(message -> System.out.println("received: " + message));
The console print out would be:
received: 1
received: 2
received: 3
received: 4
The Reactor docu also has a chapter on hot vs. cold.
When using StreamMessageListenerContainer a subscription for a consumer group can be created by calling:
receive(consumer, readOffset, streamListener)
Is there a way to configure the container/subscription so that it will always attempt to re-process any PENDING messages before moving on to polling for new messages?
The goal would be to keep retrying any message that wasn't acknowledged until it succeeds, to ensure that the stream of events is always processed in exactly the order it was produced.
My understanding is if we specify the readOffset as '>' then on every poll it will use '>' and it will never see any messages from the PENDING list.
If we provide a specific message id, then it can see messages from the PENDING list, but the way the subscription updates the lastMessageId is like this:
pollState.updateReadOffset(raw.getId().getValue());
V record = convertRecord(raw);
listener.onMessage(record);
So even if the listener throws an exception, or just doesn't acknowledge the message id, the lastMessageId in pollState is still updated to this message id and won't be seen again on the next poll.
I am following this guide- https://spring.io/guides/gs/messaging-jms/
I have few messages with higher priority that needs to be sent before any other message.
I have already tried following -
jmsTemplate.execute(new ProducerCallBack(){
public Object doInJms(Session session,MessageProducer producer){
Message hello1 =session.createTextMessage("Hello1");
producer.send(hello1, DeliveryMode.PERSISTENT,0,0); // <- low priority
Message hello2 =session.createTextMessage("Hello2");
producer.send(hello1, DeliveryMode.PERSISTENT,9,0);// <- high priority
}
})
But the messages are sent in order as they are in the code.What I am missing here?
Thank you.
There are a number of factors that can influence the arrival order of messages when using priority. The first question would be did you enable priority support and the second would be is there a consumer online at the time you sent the message.
There are many good resources for information on using prioritized messages with ActiveMQ, here is one. Keep in mind that if there is an active consumer online when you sent those messages then the broker is just going to dispatch them as they arrive since and the consumer will of course process them in that order.
I have a http server which receives some messages and must reply 200 when a message is successfully stored in a queue and 500 is the message is not added to the queue.
I would like rabbitmq to refuse my messages when the queue reach a size limit.
How can I do it?
actually you can't configure RabbitMq is such a way. but you may programatically check queue size like:
`DeclareOk queueOkStatus = channel.queueDeclare(queueOutputName, true, false, false, null);
if(queueOkStatus.getMessageCount()==0){//your logic here}`
but be careful, because this method returns number of non-acked messages in queue.
If you want to be aware of this , you can check Q count before inserting. It sends request on the same channel. Asserting Q returns messageCount which is Number of 'Ready' Messages. Note : This does not include the messages in unAcknowledged state.
If you do not wish to be aware of the Q length, then as specified in 1st comment of the question:
x-max-length :
How many (ready) messages a queue can contain before it starts to drop them from its head.
(Sets the "x-max-length" argument.)
I need to set message priority so that High priority messages are consumed before Low priority messages by Receivers.
First I tried with message.setJMSPriority() method to set the priority but it was not working in HornetQ and ActiveMQ so finally I set the priority of the Message Producer using setPriority() method and it works fine now.
Why isn't Messsge.setJMSPriority() working in any of the JMS vendor implementations and why do we need to set the priority of the Producer not the message itself to set the priority of the message? What is the use of Messsge.setJMSPriority() method then?
Any suggestion or comment is appreciated.
To answer this question all you need to do is read the API docs for the setJMSPriority method and it tells you why. Here's the relevant text.
Sets the priority level for this message.
JMS providers set this field when a message is sent. This method can be used to change the value for a message that has been received.
The JMS Provider (ActiveMQ, HornetMQ, etc) set the priority in the producer on send to either the default value of 4, or to whatever value you've set the producer to use, so setting the value before send on the message itself won't have any effect.
The following will not work:
msg.setJMSPriority(9); // Not working!
In this code, the message priority is set to 9, indicating this is a high-priority message.
However, when the message is sent, the message will have a priority of 4 (normal
priority). The reason? Like the message expiration, the JMS provider will look at the
message priority property on the sender, or on the send(..) invocation, and then invoke the setJMSPriority on the message method prior
to placing the message on the queue. Since the default message priority is 4 (normal
priority), the message priority will not be set to a high priority message, as the developer had originally intended.
Like the message expiration, there are two ways of setting the message priority: you
can invoke the setPriority() method on the MessageProducer (QueueSender or Topic
Publisher) or set the message priority when sending the message:
//set the default message priority for all messages to 9 (high)
QueueSender qSender = qSession.createSender(requestQ);
qSender.setPriority(9);
qSender.send(msg1);
//this message is low priority
qSender.send(msg2, DeliveryMode.PERSISTENT, 1, 30000);
In this example, msg1 will be sent with a priority of 9 (high priority), whereas msg2 will
be sent with a priority of 1 (low priority).
This is a JMS Specification requirement.
You should change the priority on the Message Producer.
You can read JmsTemplate http://static.springsource.org/spring/docs/3.0.6.RELEASE/spring-framework-reference/html/jms.html
Some JMS providers allow the setting of default QOS values administratively through the configuration of the ConnectionFactory.
Check isExplicitQosEnabled property.