MQ Pub/Sub v7

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Publishers and subscribers are applications that send and receive messages (publications) using the publish/subscribe method of messaging. Publishers and subscribers are decoupled from one another so that publishers do not know the destination of the information that they send, and subscribers do not know the source of the information that they receive.

The provider of the information is called a publisher. Publishers supply information about a subject without needing to know anything about the applications that are interested in the information.

The consumer of the information is called a subscriber. The subscriber decides what information it is interested in, and then waits to receive that information. Subscribers can receive information from many different publishers, and the information they receive can also be sent to other subscribers.

WebSphere MQ V7 queue managers use a Pub/Sub Engine instead of a broker to control the interactions between publishers and subscribers. The Pub/Sub Engine receives messages from publishers, and subscription requests from subscribers. The Pub/Sub Engine's job is to route the published data to the target subscribers.

mq v7.5 publib + "Publishers and subscribers"

The publisher generates a message that it wants to publish and defines the topic of the message.
A subscriber registers a request for a publication by specifying one of the following items:

• the topic, or topics, of the published messages that it is interested in.
• the subscription point from which it wants to receive publications.
• the content filter that should be applied to the published message.
• the name of the queue (known as the subscriber queue) on which publications that match the criteria selected are placed. This queue can be a cluster queue, so that publications can be distributed to clustered subscribers.

Non valid topic names :

More detail in those links

• what is new in MQ V7: Publish/Subscribe added to the MQ API - url
• webcast replay: Installation and Migration of WebSphere MQ V7 including Publish/Subscribe Configuration - url

• topic - point-to-point queue

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An application that needs to publish a message about a specific topic can do so by opening that topic and putting a message to it. There is very little difference between an application that opens a queue then puts a message to it, and one that opens a topic to put a message to it, so the application code should look very familiar to you.

If you wish to use publish/subscribe with WebSphere MQ V7 you do not require any topic objects to be defined. You can in fact go right ahead and use a topic string directly in your application. You do this by placing your topic string in the ObjectString field.

TMM42

The publisher can send a Register Publisher command message to the broker's control queue SYSTEM.BROKER.CONTROL.QUEUE to indicate that a publisher will be, or is capable of, publishing data on one or more specified topics.

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An application that wants to register an interest in information about a certain topic needs to subscribe to that topic. This can be done using the MQ API verb MQSUB. MQSUB can be thought of rather like MQOPEN. It details the resource you wish to use, and it is the point where security checks are done.

TMM42

Subscriber applications need to register their interest in receiving publications with a broker. Send the Register Subscriber command message to the SYSTEM.BROKER.CONTROL.QUEUE to register as a subscriber.

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Concept - how does it work

Theory, sample config

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See sending and receiving test publications on a topic object folder (using Explorer)

The steps are :

1. verify PSMODE for qmgr is ENABLED or code ALTER QMGR PSMODE(ENABLED) - see here

2. establish connectivity between queue managers either
   • connecting the queue managers to a WebSphere MQ cluster
   • establishing a point-to-point channel connection using a transmission queue, or queue manager alias, with the same name as the parent queue manager

3. connect a queue manager to a broker hierarchy using command ALTER QMGR PARENT(PARENT_QMGR_NAME)
   We can display it using display pubsub all command

4. define topics on one broker or queue manager that are available to publishers and subscribers on the connected queue managers. This command DEFINE TOPIC (ORANGE.TOPIC) TOPICSTR (ORANGE) DEFPRTY(ASPARENT) NPMSGDLV(ASPARENT) replace defines a topic called ORANGE.TOPIC that resolves to the topic string ORANGE

   Any attribute that is set to ASPARENT uses the attribute as defined by the parent topic of this topic. This action is repeated up the topic tree as far as the root topic, SYSTEM.BASE.TOPIC is found. See Topic trees

5. you have to register as a subscriber [cmd line ?]
   rem ---start "SUB() all publications" amqssub # QM_CNT2 start "SUB() ESPORTS publications" amqssub ESPORTS/# QM_CNT2 start "SUB() FUTBOL publications" amqssub ESPORTS/FUTBOL/# QM_CNT2 start "SUB() BCN publications" amqssub ESPORTS/+/BCN QM_CNT2
   
   You can now view a list of subscribers [cmd line ?]

6. you can register as a publisher, but it not mandatory
   You can now view registered publishers [cmd line ?]

7. now you can publish messages
   amqspub ESPORTS QM_CNT < t_tot.txt amqspub ESPORTS/FUTBOL QM_CNT < t_futbol.txt amqspub ESPORTS/FUTBOL/BCN QM_CNT < t_bcn.txt

Read writing publish/subscribe applications :

• subscriber :
  • managed MQ subscriber : MQCONN(), MQSUB(), MQGET(), MQCLOSE() and MQDISC().
  • unmanaged MQ subscriber : MQCONN(), MQOPEN(), MQSUB(), MQGET(), MQCLOSE() and MQDISC().
• publisher : MQCONN(), MQOPEN(), MQPUT(), MQCLOSE(), MQDISC()

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We need 2 queue managers :

And their objects :

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Using DISPLAY TPSTATUS TYPE(SUB) you can see the details of the current publishers on this topic string. One of the attributes returned is the Active Connection ID (ACTCONN) which links to DISPLAY CONN which shows you the details about that specific application. The Subscription ID (SUBID) links to DISPLAY SBSTATUS where we will see a single subscription with that ID since the perspective of that display is the subscription.

DISPLAY SBSTATUS which shows the run-time status of a subscription. DISPLAY SUB is slightly different it shows the more static attributes of the subscription, whether it was created using a DEFINE SUB command or an MQSUB call in an application.

TMM42

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url

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• cluster MQ - els PR es suscriuen a canvis de configuracio
• Message Broker - els Broker es suscriuen a desplegaments
• MQTT - els clients es subscriuen, els aparells publiquen
• bon exemple en aquest RedBook - companyia de transport - MQSeries Publish/Subscribe Applications
• twit boat position : good app

Queues and topics are interchangable in MQ v7. You can have the app put the message to a Topic that has two subscriber queues for the receivers, without changing the apps.

1. define a topic called Q1T, with a topic string of Q1
2. define a sub to topic object Q1T, with a destination of Q1
3. define a Q Alias called Q1Alias, target type topic with a target of Q1T
4. a put to Q1Alias will now produce a message to the Q1 local queue
5. define another sub to topic object Q1T, this time with a destination of Q2
6. a put to Q1Alias will now produce 2 messages, one to Q1 and one to Q2.

url

Define a TOPIC that acts as the destination of the sending app and two subscriptions to the "real" destination queues.

Another seq: App A is putting to a local q called Q1. App B is pulling from Q1. You have MQ 7 and want to duplicate the messages but do not want to change the sending or receiving app code.

• define a topic called Q1T, with a topic string of Q1
• define a sub to topic object Q1T, with a destination of Q1
• define a Q Alias called Q1Alias, target type topic with a target of Q1T
• a put to Q1Alias will now produce a message to the Q1 local queue
• define another sub to topic object Q1T, this time with a destination of Q2
• a put to Q1Alias will now produce 2 messages, one to Q1 and one to Q2.

The only change in the original setup is that App A puts to Q1Alias instead of Q1. App A and App B don't know they are using Pub Sub. The subscriptions are created by the MQ Admin using admin commands.

url

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• amb quin criteri escollir de fer servir cues managed o unmanaged ?
• que fer amb un error
  2432 0x00000980 MQRC_SUB_ALREADY_EXISTS
• com trassejar TOTES les publicacions que es fan ?
  Amb un Subscriber a "#" ?

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• PubLib
• pub/sub user's guide : v 1.0, v 1.2
• Writing a simple publish/subscribe application connecting through MQ
• Education Assistant, 5x PDFs ;
• distributed pub/sub - nice PPT
• Performing publish/subscribe migration from MQ V6 pdf.
• What's new in publish/subscribe in WebSphere MQ Version 7.0 url
• Morag
• Few docs : distributed. distributed, migration, migration, pub/sub troubleshooting tools,
• nice sample ; another case