I'm trying to configure a queue that is aware of the events that are being processed.
Questions
Does this make sense? :)
Is it possible to configure/customize ActiveMQ?
Are there any other library that can be "easily" configured to handle such cases? Kafka?
Problem
The queue contains events. Each event is associated with an object. A consumer takes the event from the queue and performs a task. Each event should be taken only by exactly one consumer.
Constraints
Events for the same object cannot be processed concurrently.
But events for different objects should be processed in parallel.
Example
The queue is
ObjectA-Event1
ObjectA-Event2
ObjectB-Event1
ObjectC-Event1
The Consumer1 should receive ObjectA-Event1 from the queue. The Consumer2 should receive ObjectB-Event1 from the queue and not the ObjectA-Event2. The ObjectA-Event2 should be available for consumers only when the first consumer completes the task for the ObjectA-Event1.
It looks to me like you should use message groups. Messages for each object should be in the same group so that they are received by the same consumer and processed serially. Messages in different groups are free to be processed by different consumers.
Related
I can't find this information anywhere. I have two queues, #JmsListener(destination = "p1"), #JmsListener(destination = "p2"). How can I make sure I only process 1 message at a time, even though I am listening to 2 queues, and also how do I configure the polling of what queue I get messages from first, that is after processing a message I want to poll p1 first. Or do weighted polling: p1:90%, p2:10%. Etc.
Basically I am asking how to implement priority processing of messages for Spring. I'm using SQS which doesn't support priorities.
Use one of the JmsTemplate receive() or receiveAndConvert() methods instead of the message-driven model.
Use transactions if you want to ensure no message loss.
I have implemented the example from the RabbitMQ website:
RabbitMQ Example
I have expanded it to have an application with a button to send a message.
Now I started two consumer on two different computers.
When I send the message the first message is sent to computer1, then the second message is sent to computer2, the thrid to computer1 and so on.
Why is this, and how can I change the behavior to send each message to each consumer?
Why is this
As noted by Yazan, messages are consumed from a single queue in a round-robin manner. The behavior your are seeing is by design, making it easy to scale up the number of consumers for a given queue.
how can I change the behavior to send each message to each consumer?
To have each consumer receive the same message, you need to create a queue for each consumer and deliver the same message to each queue.
The easiest way to do this is to use a fanout exchange. This will send every message to every queue that is bound to the exchange, completely ignoring the routing key.
If you need more control over the routing, you can use a topic or direct exchange and manage the routing keys.
Whatever type of exchange you choose, though, you will need to have a queue per consumer and have each message routed to each queue.
you can't it's controlled by the server check Round-robin dispatching section
It decides which consumer turn is. i'm not sure if there is a set of algorithms you can pick from, but at the end server will control this (i think round robin algorithm is default)
unless you want to use routing keys and exchanges
I would see this more as a design question. Ideally, producers should create the exchanges and the consumers create the queues and each consumer can create its own queue and hook it up to an exchange. This makes sure every consumer gets its message with its private queue.
What youre doing is essentially 'worker queues' model which is used to distribute tasks among worker nodes. Since each task needs to be performed only once, the message is sent to only one node. If you want to send a message to all the nodes, you need a different model called 'pub-sub' where each message is broadcasted to all the subscribers. The following link shows a simple pub-sub tutorial
https://www.rabbitmq.com/tutorials/tutorial-three-python.html
My system has a constrain for specific consumer that messages should be handled in order, one after the other. To implement that we set the concurrency to 1.
Now we want to scale out and add more instance of this consumer.
To keep the order I want to use distributed lock manager like 'RedLock'. It can tell each consumer if it is OK to fetch the next message.
I work with RabbitMq and my question is if there is kind of observer event that comes before getting messages from the queue. In other words I need a way to enable/disable the operation of polling messages from the queue.
I send a java object to a queue from a thread. The relavent MDB's onMessage is invoked with a message from the queue. onMessage, I match a key present in the message with a key in a cache, if key is not present I throw a custom runtimeexception just to make the container redeliver this message. (I have another autonomous system that adds key to the cache from the external system response, it may be little slow by 3-5 seconds)
In such case, does this container add this unprocessed message to the end of the queue, or is it redelivered immediately? is there a way to delay the redelivery time? assuming the queue is always filled with ~550 messages every second.
regards
There's current a redelivery delay feature on HornetQ but all the subsequent messages are delivered fine.
There's a feature request in place to hold the queue for some time if a redelivery happens but that has not been implemented yet.
but if you have multiple consumers on the queue the order will be spread with your consumers anyways. You could use message-grouping and add a sleep on your onMessage if deliveryCount > 1. The message grouping is to guarantee no other consumer (or another MDB instance) will receive the messages out of order.
Depending on how you're application is done, and depending on your requirements you may want to only allow a single instance of your MDB.
Also: look at the consumer-window-size where you can select no buffering on the client which has a better behaviour when you have multiple consumers or multiple mdb instances.
I was wondering what is the difference between a JMS Queue and JMS Topic.
ActiveMQ page says
Topics
In JMS a Topic implements publish and subscribe semantics. When you publish a message it goes to all the subscribers who are
interested - so zero to many subscribers will receive a copy of the
message. Only subscribers who had an active subscription at the time
the broker receives the message will get a copy of the message.
Queues
A JMS Queue implements load balancer semantics. A single message will be received by exactly one consumer. If there are no
consumers available at the time the message is sent it will be kept
until a consumer is available that can process the message. If a
consumer receives a message and does not acknowledge it before closing
then the message will be redelivered to another consumer. A queue can
have many consumers with messages load balanced across the available
consumers.
I want to have 'something' what will send a copy of the message to each subscriber in the same sequence as that in which the message was received by the ActiveMQ broker.
Any thoughts?
That means a topic is appropriate. A queue means a message goes to one and only one possible subscriber. A topic goes to each and every subscriber.
It is simple as that:
Queues = Insert > Withdraw (send to single subscriber) 1:1
Topics = Insert > Broadcast (send to all subscribers) 1:n
Topics are for the publisher-subscriber model, while queues are for point-to-point.
A JMS topic is the type of destination in a 1-to-many model of distribution.
The same published message is received by all consuming subscribers. You can also call this the 'broadcast' model. You can think of a topic as the equivalent of a Subject in an Observer design pattern for distributed computing. Some JMS providers efficiently choose to implement this as UDP instead of TCP. For topic's the message delivery is 'fire-and-forget' - if no one listens, the message just disappears. If that's not what you want, you can use 'durable subscriptions'.
A JMS queue is a 1-to-1 destination of messages. The message is received by only one of the consuming receivers (please note: consistently using subscribers for 'topic client's and receivers for queue client's avoids confusion). Messages sent to a queue are stored on disk or memory until someone picks it up or it expires. So queues (and durable subscriptions) need some active storage management, you need to think about slow consumers.
In most environments, I would argue, topics are the better choice because you can always add additional components without having to change the architecture. Added components could be monitoring, logging, analytics, etc.
You never know at the beginning of the project what the requirements will be like in 1 year, 5 years, 10 years. Change is inevitable, embrace it :-)
Queues
Pros
Simple messaging pattern with a transparent communication flow
Messages can be recovered by putting them back on the queue
Cons
Only one consumer can get the message
Implies a coupling between producer and consumer as it’s an one-to-one relation
Topics
Pros
Multiple consumers can get a message
Decoupling between producer and consumers (publish-and-subscribe pattern)
Cons
More complicated communication flow
A message cannot be recovered for a single listener
As for the order preservation, see this ActiveMQ page. In short: order is preserved for single consumers, but with multiple consumers order of delivery is not guaranteed.
If you have N consumers then:
JMS Topics deliver messages to N of N
JMS Queues deliver messages to 1 of N
You said you are "looking to have a 'thing' that will send a copy of the message to each subscriber in the same sequence as that in which the message was received by the ActiveMQ broker."
So you want to use a Topic in order that all N subscribers get a copy of the message.
TOPIC:: topic is one to many communication... (multipoint or publish/subscribe)
EX:-imagine a publisher publishes the movie in the youtub then all its subscribers will gets notification....
QUEVE::queve is one-to-one communication ...
Ex:-When publish a request for recharge it will go to only one qreciever ...
always remember if request goto all qreceivers then multiple recharge happened so while developing analyze which is fit for a application
Queue is JMS managed object used for holding messages waiting for subscribers to consume. When all subscribers consumed the message , message will be removed from queue.
Topic is that all subscribers to a topic receive the same message when the message is published.