I'm trying to create new subscriber with 'Destination name' as local-queue-name, but for that I need non-durable subscriber.
When creating new subscriber in MQ, using MQSC or MQ-Explorer, how do I make it non-durable?
Is there any way to change it (alter) after it has been created?
Thanks.
Non-durable subscriptions are active as long as the application that created them is active. Once the application ends or application closes connection to queue manager, these subscriptions are removed. What this means is non-durable subscriptions can only be created programmatically using MQSUB(in C language) or it's equivalent method in Java/C#.
Non-durable subscriptions can not be created using MQSC or MQExplorer. You can create durable subscriptions using MQSC/MQExplorer.
Non-durable subscriptions exist only as long as the subscribing application's connection to the queue manager remains open. The subscription is removed when the subscribing application disconnects from the queue manager either deliberately or by loss of connection. When the connection is closed, the information about the subscription is removed from the queue manager, and will no longer be shown if you display subscriptions using the DISPLAY SBSTATUS command. No more messages will be put to the subscriber queue.
For more information, see Subscription durability
Related
Both the Solace queue and my program are subscribing to #LOG/INFO/SUB_ADD/DEVICE/ID/123.
When a new device which connects and subscribe to DEVICE/ID/123, both of them can successfully receive the subscribe event.
But, if I set subscription as #LOG/INFO/SUB_ADD/DEVICE/ID/>, only the solace queue receives the event.
Why can't my program receive the subscription event?
The problem persists even after my program sets it's subscription to #LOG/>.
One possible problem here is that there is an ACL rule preventing your application to subscribe to one or more topics in #LOG/INFO/SUB_ADD/DEVICE/ID/>. This can be easily verified with show log acl subscribe-topic.
If this is not the case, please revert back with the CLI outputs of show client <client-name> stats detail and show client <client-name> subscriptions to look further into the issue.
Is there any way we can know when a consumer disconnects from a queue or when a queue is deleted?
The requirement is as follows:
I'm building a system in which multiple clients can subscribe to certain events from the system. All clients create their own queue and registers themselves with the system using some sort of authentication. The system, as the events are generated, filters the events and forwards them to clients who are eligible for them.
I have implemented a POC for most part of it and it works well. An issue that I'm not able to fix is that, if a client just disconnects from the queue (due to program termination or so), the registration still exists and the system keeps trying to push messages to that client.
So we would like to be notified when a client disconnects or a queue gets deleted so that we can remove that client's registration data and no longer push messages to him.
Let your publisher utilize Confirms (aka Publisher Acknowledgements) and make client queue be exclusive and transient, so only one client at a time will be consuming from one queue and after it disconnection it will be deleted.
If you publish message that get routed to only one queue and that queue gone (assume you utilize publisher confirms and publish message with mandatory flag set) publisher will be notified that message cannot be routed with that message returned back to it, so you can stop publishing messages.
For details see How Confirms Work section in RabbitMQ blog post "Introducing Publisher Confirms" and Confirms (aka Publisher Acknowledgements) official docs.
Is it possible to configure the topic to store a copy of just the last message and send this to new connections without knowing client identifiers or other info?
Update:
From the info provided by Shashi I found this two pages where they describe a use case similar to mine (applied over stock prices) by using retroactive consumer and a subscription recovery policy. How ever I'm not getting the desired behaviour. What I currently do is:
Include in the activemq the folowing lines in the policyEntry for topic=">"
<subscriptionRecoveryPolicy>
<fixedCountSubscriptionRecoveryPolicy maximumSize="1"/>
</subscriptionRecoveryPolicy>
Add to the URL used to connect to the brocker (using activemq-cpp) consumer.retroactive=true.
Set the consumer has durable. (But I strongly think this is not want since I only need the last one, but without it I didn't get any message when starting the consumer for the second time)
Start up the broker.
Start the consumer.
Send a message to the topic using the activemq web admin console. (I receive it in the consumer, as expected)
Stop consumer.
Send another message to the topic.
Start consumer. I receive the message, also as expected.
However, if the consumer receives a message, then it goes offline (stop process) and then I restart it, it doesn't get the last message back.
The goal is to whenever the consumer starts get the last message, no mater what (obviously, except when there weren't messages sent to the topic).
Any ideas on what I'm missing?
Background:
I have a device which publishes his data to a topic when ever its data changes. A variable number of consumer may be connected to this topic, from 0 to less than 10. There is only one publisher in the topic and always publish all of his data as a single message (little data, just a couple of fields of a sensor reading). The publication rate of this information is variable, not necessarily time based, when something changes a new updated message is sent to the broker.
The problem is that when a new consumer connects to the topic it has no data of the device readings until a new message is send to the topic by the device. This could be solve by creating an additional queue so new connections can subscribe to the topic and then request the device for the current reading through the queue (the device would consume the queue message which would be a request for data, and then response in the same queue).
But Since the messages send to the topic are always information complete I was wondering if is it possible to configure the topic to store a copy of just the last message and send this to new connections without know client identifiers or other info?
Current broker in use is ActiveMQ.
What you want is to have retroactive consumers and to set the lastImageSubscriptionRecoveryPolicy subscription recovery policy on the topic. Shashi is correct in saying that the following syntax for setting a consumer to be retroactive works only with Openwire
topic = new ActiveMQTopic("TEST.Topic?consumer.retroactive=true");
In your case, what you can do is to configure all consumers to be retroactive in broker config with alwaysRetroactive="true". I tested that this works even for the AMQP protocol (library qpid-jms-client) and I suspect it will work for all protocols.
<destinationPolicy>
<policyMap>
<policyEntries>
<policyEntry topic="FOO.>" alwaysRetroactive="true">
<subscriptionRecoveryPolicy>
<lastImageSubscriptionRecoveryPolicy />
</subscriptionRecoveryPolicy>
</policyEntry>
The configuration example is taken from https://github.com/apache/activemq/blob/master/activemq-unit-tests/src/test/resources/org/apache/activemq/test/retroactive/activemq-message-query.xml
Messaging providers (WebSphere MQ for example) have a feature called Retained Publication. With this feature the last published message on a topic is retained by the messaging provider and delivered to a new consumer who comes in after a message has been published on a given topic.
Retained Publication may be supported by Active MQ in it's native interface. This link talks about consumer.retroactive which is available for OpenWire only.
A publisher will tell the messaging provider to retain a publication by setting a property on the message before publishing. Below is how it is done using WebSphere MQ.
// set as a retained publication
msg.setIntProperty(JmsConstants.JMS_IBM_RETAIN, JmsConstants.RETAIN_PUBLICATION)
Spring Message Listener Container doc says:
http://static.springsource.org/spring/docs/2.5.x/api/org/springframework/jms/listener/AbstractMessageListenerContainer.html#setDurableSubscriptionName%28java.lang.String%29
The durable subscription name needs to be unique within this client's
JMS client id. Default is the class name of the specified message
listener. Note: Only 1 concurrent consumer (which is the default of
this message listener container) is allowed for each durable
subscription.
I thought, we can handle concurrent messages at the same time. Am I missing something?
Yes, the documentation is correct. At any point of time there can be only one consumer receiving messages for a durable subscription. All durable subscriptions are identified by a unique id. If one consumer is already receiving messages using an id, another attempt create a consumer with the same id for that durable subscription will fail.
I've had this problem before and our log was full of warnings complain about client id is already in use.
Virtual Topic is an option for ActiveMQ: the idea is similar to what #brainOverflow described, it's a combination of topic and queues. The producer sends the message to a topic which is subscribed by queues and each queue receives a copy of the message.
http://activemq.apache.org/virtual-destinations.html
I am using ActiveMQ as a JMS implementation server in my application. Scenario is like, there is a topic over which I have many durable subscribers which consumes the published message and a message listener which save the data from message object to central DB server. There is a producer thread which keeps on publishing persistent message over the same topic. I am using KahaDB for persistent Message Store. As soon as a message is published, kahaDB creates a data log file in message store to persist message until all durable subscriber consume it. I want to know if at any point, I shutdown the JMS server and delete all the data log files, what would be the impact. Will it be just that few durable subscriers will not receive a message which was there in data log files for them to be consumed or is there a possibility that few message didn't got saved in central database which is done by message listener over this topic.
Any hint or help is greatly appreciated......
Thanks in advance.
If you stop and start your broker, regardless of whether you delete your data files or not, topic consumer that have not already received a published message will no longer receive it. The reason behind this is that messages sent to a topic will not be written out to the persistent message store.
Durability and persistence are not the same things. A durable subscription tells the broker to preserve the subscription state in case the subscriber disconnects - any messages sent while the consumer is disconnected will be kept around. A non-durable subscription on the other hand is finite; if a subscriber disconnects, it missed any messages sent in the interim. All messages are stored in memory, and will not survive a broker restart.
Message persistence on the other hand stores messages for eventual delivery. This guards against catastrophic failure, or for later delivery to consumers who might not yet be active.
If you want to broadcast messages using pub-sub, and have the subscriptions appear durable and survive broker restarts you should use virtual destinations instead of durable subscriptions.
No messages, persistent or non-persistent, will survive switching the broker off and deleting the data directory.