I have a Tibco EMS topic subscriber which I need to load balance among different instances. Each published message to the topic needs to be received by one (and only one) instance of each subscriber load balance group.
Just using global topics and balanced EMS connections (tcp://localhost:7222|tcp://localhost:7224) results in the same message received by all instances of each subscriber load balance group, producing duplicates.
Do you know any alternative for load balancing topic subscribers?
You can:
A) Bridge the topic to a queue and reconfigure your subscribers to read from the queue. Queues behave differently to topics in that a message is only obtained by one subscriber rather than all.
B) Create a number of durable subscribers on the topic with selectors that divide messages between the durables. E.g. If a message has a property 'id' that is sequentially increasing:
create durable topic DURABLENAME1 selector="(id - 2 * (id / 2)) = 0"
create durable topic DURABLENAME2 selector="(id - 2 * (id / 2)) = 1"
The selector is just a modulo so half the messages will go on one durable, and half on the other.
With EMS 8.0 new concept shared subscription is added with these only one subscription receives messages with the same subscription name go through the EMS user guide docs it may help you.
While both previous answers are valid, however the most natural approach would be to not use topics at all.
Using queues instead pf topics does the whole job (loadbalancing in round robin fashion).
Related
We have an IBM MQ JMS queue and want to distribute the data into multiple consumers for load balancing. So if we write two JMS Clients to consume from same JMS queue what will happen? Will Messages be equally distributed across both consumers since one consumer will delete the data after it is read? Is there a possibility for data duplication, like if the same message is read by both consumers in a race condition?
My comments below are based on destructive get and not a browse get.
So if we write two JMS Clients to consume from same JMS queue what
will happen?
They will both consume messages.
Will Messages be equally distributed across both consumers since one
consumer will delete the data after it is read?
No. The "hot" consumer will be feed the next available message, assuming it is "getting" a message again before the next message arrives.
Is there a possibility for data duplication, like if the same message
is read by both consumers in a race condition?
Not if you are performing a destructive get (the default).
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
This is the scenario:
I know that using latest API related to Spring kafka (like Spring-integration-kafka 2.10) we can do something like:
#KafkaListener(id = "id0", topicPartitions = { #TopicPartition(topic = "SpringKafkaTopic", partitions = { "0" }) })
#KafkaListener(id = "id1", topicPartitions = { #TopicPartition(topic = "SpringKafkaTopic", partitions = { "1" }) })
and with that read from different partitions related to the same kafka topic.
I'm wondering if we can do the same using, for example spring-integration-kafka 1.3.1
I didn't find any tip about how to do that (I'm interesting in the xml version).
In Kafka you can decide from which topics you want to read,
but we can't decide from which partitions we want to read, it's up to Kafka to decide that in order to avoid reading the same message more than once.
Consumers don't share partitions for reading purposes, by Kafka definition.
If you'll have more consumers than partitions some consumers will stay idle and won't consume from any partition. for example, if we'll have 5 consumers and 4 partitions, 1 consumer will stay idle and won't consume data from kafka broker.
The actual partition assignment is being done by a kafka broker (the group coordinator) and a leader consumer. we can't control that.
This definition helped me the most:
In Apache Kafka, the consumer group concept is a way of achieving two
things:
Having consumers as part of the same consumer group means providing the “competing consumers” pattern with whom the messages
from topic partitions are spread across the members of the group. Each
consumer receives messages from one or more partitions
(“automatically” assigned to it) and the same messages won’t be
received by the other consumers (assigned to different partitions). In
this way, we can scale the number of the consumers up to the number of
the partitions (having one consumer reading only one partition); in
this case, a new consumer joining the group will be in an idle state
without being assigned to any partition.
Having consumers as part of different consumer groups means providing the “publish/subscribe” pattern where the messages from
topic partitions are sent to all the consumers across the different
groups. It means that inside the same consumer group, we’ll have the
rules explained above, but across different groups, the consumers will
receive the same messages. It’s useful when the messages inside a
topic are of interest for different applications that will process
them in different ways. We want all the interested applications to
receive all the same messages from the topic.
From here Don't Use Apache Kafka Consumer Groups the Wrong Way!
I have a Rabbit Topic with multiple (say 2)subscribers which is running in a load balanced application server cluster ( say 3 ) .
So will the message will get delivered to all (2 X 3 ) subscribers of all listeners in a clustered environment or only 2 listeners ?
There's no such thing as a "topic" in rabbitmq (amqp).
The closest thing to a JMS topic for your scenario is a fanout exchange with 2 queues bound to it. Each queue gets a reference to a message sent to the exchange so both consumers (one per queue) gets a copy of the message.
If you have multiple consumers (e.g. 3) on each queue, the messages in that queue are distributed round-robin fashion to those consumers. Only one consumer per queue gets a message.
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.