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.
Related
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'm trying to understand how rabbitmq works with multiple consumer and prefetch_count.
I have three consumers consuming on the same queue and all of these consumers have configured with the QoS prefetch_count = 200.
Now assuming at a certain point I have unlimited backlog messages in the queue and consumers A,B,C are connecting to the queue, would A get message 1-200, B get 201-400, C get 401-600 from the queue simultaneously? That seems like message 1, 201, 401 got processed at the first place compared to the rest. Somehow I don't want that, I'd like to have these messages being processed sequentially.
If that's the case I guess this implies that the messages may be processed disordered based on how consumers are setup, even though the queue follows FIFO.
Or should I set prefetch_count = 1 to make sure of REAL FIFO?
Edited:
Just set up a local env of rabbitmq and experimented a bit. I used a producer to bombard a queue with numbers 0 to 100000 sequentially to accumulate backlog messages in a queue. Later on, I had two consumers A, B consuming messages from that queue with prefetch_count = 200.
From what I observed, A got 0-199 and B got numbers 200-399 at very beginning. However, A started getting numbers {401, 403, 405, 406 ...} and B gets {400, 402, 404, ...} after that.
I guess A and B got non-skipped messages at the beginning was because I wasn't strictly spinning up these two consumers simultaneously. But the following pattern explains well how prefetch_count works. It doesn't necessarily send consumers consecutive messages(I knew it's processed in a round robin fashion, but I guess this is more intuitive with an experiment). There's no guarantee in what order the messages will be processed if using prefetch_count.
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.)
Up until now, my RabbitMQ consumer clients have used a prefetch value of 1. I'm looking to increase the value in order to gain performance. If I set the value to 2, will the RabbitMQ server send each consumer 2 messages at once such that I will need to parse the two messages and store the second one in a List until the first is processed and acknowledged? Or will the API handle this behind the scenes?
I'm using the Java AMQP client library:
ConnectionFactory factory = new ConnectionFactory();
...
Connection connection = factory.newConnection();
Channel channel = connection.createChannel();
channel.basicQos(2);
QueueingConsumer consumer = new QueueingConsumer(channel);
channel.basicConsume(CONSUME_QUEUE_NAME, false, consumer);
while (!Thread.currentThread().isInterrupted()) {
try {
QueueingConsumer.Delivery delivery = consumer.nextDelivery();
String m = new String(delivery.getBody(), "UTF-8");
// Will m contain two messages? Will I have to each message and keep track of them within a List?
...
}
The api handles this behind the scenes, so there are no worries there for you.
Regarding which message gets where, RMQ will just deliver by using round robin, that is if you have the queue: 1 2 3 4 5 6 and consumer1 and consumer2.
consumer1 will have 1 3 5
consumer2 will have 2 4 6
Should the connection die to any of your consumers the prefetched messages will be redelivered to the active consumers using the same delivery method.
This should be interesting reading and a good starting point to figure more exactly what happens:
Tutorial no.2 which I'm sure you've read
Reliability
The api internally queue messages in a blocking queue.
Setting the prefetch count more than 1 is actually a good idea since your worker need not wait for each and every message to arrive. It can read up to N messages (where N is the prefetch count). It can start working on a message as soon as it has finished the previous one.
Also, you have the option to acknowledge multiple messages at once instead of acknowledging individually.
channel.basicAck(lastDeliveryTag, true);
boolean true indicates to acknowledge all the messages upto and including the supplied lastDeliveryTag
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.