Is there any way in RabbitMQ to have multiple consumers get the same message from the same queue?
I need to send the same message to anyone who's listening but also ensure that someone deals with it. Basically, I need the fanout functionality of an exchange combined with the basic.ack functionality of a queue. Is there any way to accomplish this in a scalable way?
If you are trying to ensure that the message is properly processed, acknowledgement already provides this capability. If your consumer is unable to process the message and does not provide an ack it will be requeued and processed again by the next available consumer. Implementing multiple competing consumers on the same queue will give you round-robin delivery, allowing the other consumers a chance for success.
How scalable this will be depends on how long it takes to process each message compared to the incoming rate, queue durability, prefetch and how many competing consumers you have on the queue.
Related
Let's suppose we have one producer, one queue and some consumers which are subscribed on queue.
Producer -> Queue -> Consumers
Queues contains messages about life events. These messages should receive all consumers.
When queue will be erased?
When all consumers get message?
Or when one of consumers confirm message with flag ack (true)?
And how to manage priority, who from consumers must to get message first/last (don't confuse with message priority).
As instance I have 10 consumers and I want that the fifth consumer get message first, remaining consumers later after specified time.
Be careful: when there are many consumers on one queue, only one of them will receive a given message, provided that it is consumed and acked properly. You need to bind as many queues as consumers to an exchange to have all consumers receive the message.
For your priority question, there is no built-in mecanism to have consumers receive the same message with a notion of priority: consumer priority exists (see https://www.rabbitmq.com/consumer-priority.html), but it is made to have consumer receive a given message before the others on a given queue, so the other consumers won't receive this message. It you need to orchestrate the delivery of your messages, you have to think of a more complex system (maybe a saga or a resequencer?).
Note that you can delay messages using this pattern. Again, this requires having multiple queues.
Finally, there are many scenarios when a queue is deleted. Take a look at the documentation, these are well explained.
I have a producer and a consumer. Multiple instances of the consumer are running. When producer publishes a message, my intention is to consume the message by all the instances. So, I am using the direct exchange. Producer publishes a message to the direct exchange with a topic. Consumers are listening to that topic with the exclusive queue. This process is working fine when the consumer is up and producer publishes a message. But when consumers are down and producer publishes a message, consumers are not consuming this message when up.
I googled about the issue. A suggestion was to use named queue. But if I use named queue, messages will be consumed following the round-robin algorithm. That does not meet my expectation to consume the same message by all the consumers.
Is there any other solution?
Appreciated your help.
There are two solutions to your issue.
Using named queue is one of them.
Set your exchange in fanout mode and subscribe your named queues to it. Doing so, when a publisher send a message in your exchange, it will be dispatched to all the queues listening.
You can then have one or more consumer for each queue (allowing you to scale). You'll have to define a named queue / consumer. When one consumer disconnect, his queue still receive messages and when he comes back he can consume them.
You should be able to do what you want that way.
The other way is more for your personnal knowledge since you said you want to use RabbitMQ. But in that particular case you could use Kafkha, your consummer could then, after reconnection, resume at the message index he was when he disconnected.
Please update me if it doesn't work :)
So I'm testing RabbitMQ in one node. Plain and simple,
One producer sends messages to the queue,
Multiple consumers take tasks from that queue.
Currently consumers execute thousands of messages per second, they are too fast so I need them to slow down. Managing consumer-side throttling is not possible due to network unreliable nature.
Collectively consumers must not take more than 10 messages per second altogether from that queue.
Is there a way to configure RabbitMQ so as the queue dispatches a maximum of 10 messages per second?
If I remember correctly, once Rabbit MQ has delivered a message to the queue, it's up to consumers to consume a message. There are various consumers in different languages, you haven't mentioned anything specific, so I'm giving a generic answer.
In my understanding, you shouldn't try to impose any restrictions on Rabbit MQ itself, instead, consider implementing connection pool of message consumers that will be able to handle not more than X messages simultaneously on the client side. Alternatively, you can provide some kind of semaphore at the handler itself, but not on the Rabbit MQ server itself.
I am starting with ActiveMQ and I have a usecase. i have n producers sending messages into a Queue Q1. I want to stop the delivery of messages (i.e. i do not want consumers to consume those messages). I want to store the messages for sometime without those being consumed.
I was looking at ways this can be achieved. These two things came into my mind based on what i browsed through.
Using Mirrored queues, so that I can wiretap the messages and save into a virtual queue.
Possibly stop consumers from doing a PULL on the queue.
Another dirty way of doing this is by making consumers not send ack messages once its consumed a message from the queue.
We are currently not happy with either of these.
Any other way you can suggest.
Thanks in advance.
If you always want message delivery to be delayed you can use the scheduler feature of ActiveMQ to delay delivery until a set time or a fixed delay etc.
Other strategies might also work but it really up to you to design something that fits your use case. You can try to use Apache Camel to define a route that implements the logic of your use case to either dispatch a message to a Queue or send it to the scheduler for delayed processing. It all really depends on your use case and requirements.
I'm in a phase of learning RabbitMQ/AMQP from the RabbitMQ documentation. Something that is not clear to me that I wanted to ask those who have hands-on experience.
I want to have multiple consumers listening to the same queue in order to balance the work load. What I need is pretty much close to the "Work Queues" example in the RabbitMQ tutorial.
I want the consumer to acknowledge message explicitly after it finishes handling it to preserve the message and delegate it to another consumer in case of crash. Handling a message may take a while.
My question is whether AMQP postpones next message processing until the previous message is ack'ed? If so how do I achieve load balancing between multiple workers and guarantee no messages get lost?
No, the other consumers don't get blocked. Other messages will get delivered even if they have unacknowledged but delivered predecessors. If a channel closes while holding unacknowledged messages, those messages get returned to the queue.
See RabbitMQ Broker Semantics
Messages can be returned to the queue using AMQP methods that feature a requeue parameter (basic.recover, basic.reject and basic.nack), or due to a channel closing while holding unacknowledged messages.
EDIT In response to your comment:
Time to dive a little deeper into the AMQP specification then perhaps:
3.1.4 Message Queues
A message queue is a named FIFO buffer that holds message on behalf of a set of consumer applications.
Applications can freely create, share, use, and destroy message queues, within the limits of their authority.
Note that in the presence of multiple readers from a queue, or client transactions, or use of priority fields,
or use of message selectors, or implementation-specific delivery optimisations the queue MAY NOT
exhibit true FIFO characteristics. The only way to guarantee FIFO is to have just one consumer connected
to a queue. The queue may be described as “weak-FIFO” in these cases. [...]
3.1.8 Acknowledgements
An acknowledgement is a formal signal from the client application to a message queue that it has
successfully processed a message.[...]
So acknowledgement confirms processing, not receipt. The broker will hold on to the message until it's gotten acknowleged, so that it can redeliver them. But it is free to deliver more messages to consumers even if the prededing messages have not yet been acknowledged. The consumers will not be blocked.