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MQSeries.net Forum IndexGeneral IBM MQ SupportDead Letter Queue for Each Topic Subscription

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EricL
PostPosted: Sat Oct 19, 2019 8:27 am Post subject: Dead Letter Queue for Each Topic Subscription Reply with quote

Voyager

Joined: 10 Oct 2014
Posts: 93

Hi,

We have a queue manager instance with a topic created on it, there would be multiple subscriptions to the same topic, question is: Can we create one dead letter queue for each subscription so that it is easy to do trouble shooting for each subscription? If can, how to do it?

Thanks....
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PaulClarke
PostPosted: Sat Oct 19, 2019 12:09 pm Post subject: Reply with quote

Guardian

Joined: 17 Nov 2005
Posts: 949
Location: New Zealand

This feels like a solution to a problem. ie. you are trying to solve something. What is the problem you have, or think you have ? Are you concerned about messages not being delivered to subscribers ? Perhaps when the subscribers are not running ? Or is there some other concern here.
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EricL
PostPosted: Mon Oct 21, 2019 1:11 pm Post subject: Reply with quote

Voyager

Joined: 10 Oct 2014
Posts: 93

We are at the early stage of building up an environment where Websphere Application Servers will connect to MQ server through subscriptions, but there is only one QM instance available for 3 websphere application servers to make connection to, to help future trouble shooting, we'd like to know if we can create 3 different DLQs for each subscription, if yes, how to do that.

Please provide advice.

Thanks
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hughson
PostPosted: Mon Oct 21, 2019 7:47 pm Post subject: Reply with quote

Grand Master

Joined: 09 May 2013
Posts: 1283
Location: Bay of Plenty, New Zealand

You still haven't described the problem you are trying to solve. I'm sure knowing this would help our answers to be more detailed.

When a published message is unable to be delivered to a subscriber queue (and the topic is configured with USEDLQ(YES)) then the message will be placed on the Dead Letter queue. When you look at the message that is placed on the Dead Letter queue, you will see that the message is pre-pended with a header called an MQDLH (Dead Letter Header). This header contains several useful bits of information including (but not limited to):-
  • The reason for the failure to put the message on the subscriber queue, e.g. MQRC_Q_FULL
  • The name of the subscriber queue
  • The date and time the message was put
So, if you were able to create a Dead-Letter queue per subscriber queue, you wouldn't learn anything more than you can already discover from the MQDLH header when using a single central Dead Letter queue.

When there is a failure, you have the name of the queue - this means you can directly find the subscription that is problematic by using a command such as the following:-
Code:
DISPLAY SUB(*) WHERE(DEST EQ <q-name-from-mqdlh>) ALL

So, please do now let us know the problem you foresee with using the central Dead Letter queue, and let us help you further.

Cheers,
Morag
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EricL
PostPosted: Thu Oct 24, 2019 3:22 pm Post subject: Reply with quote

Voyager

Joined: 10 Oct 2014
Posts: 93

Thanks for your interesting in the topic, the reply is so informative, I think I already find the solution for the potential problem.

Let me recap our scenarios here:

1. There are 3 topic subscriptions from 3 different Websphere Application Servers to subscribe to the same topic on a queue manager
2. To help future trouble shooting, we were thinking to create 3 DLQs for each subscription, so that these subscriptions won't affect each other when there is delivery issue come out

As Morag specified, the default DLQ actually is good enough for providing all the info when there is undelivered message to subscription queue, MQDLH (Dead Letter Header) would contain several useful bits of information including (but not limited to):-
a: The reason for the failure to put the message on the subscriber queue, e.g. MQRC_Q_FULL
b: The name of the subscriber queue
c: The date and time the message was put

So in our case, since there would be 3 different subscription queues for each different subscription, when there is message delivery issue occur, subscription queue name would be captured in MQDLH, it surely helps us easily figure out which subscription got problem.

Thanks so much, very appreciate your help.

Frankly speaking, I still have no clue how to create different DLQ for different subscription

Thanks again !
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PeterPotkay
PostPosted: Thu Oct 24, 2019 5:30 pm Post subject: Reply with quote

Poobah

Joined: 15 May 2001
Posts: 7582

EricL wrote:

Frankly speaking, I still have no clue how to create different DLQ for different subscription

There is no way as a queue manager can only have one DLQ.

However, you may want to create a separate backout queue for each subscriber queue, and set the backout queue name and threshold on each subscriber queue. While this won't help with delivery problems, it will be useful if the subscriber gets a message off its subscriber queue and finds it can't process it, backing it out to the input queue. To avoid an endless loop, a backout queue can be used.

Its typical to have a separate backout queue per input (subscriber) queue, because messages put to backout queues usually do not have a header added that details from which input queue it was backed out.
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gbaddeley
PostPosted: Tue Oct 29, 2019 3:43 pm Post subject: Reply with quote

Jedi

Joined: 25 Mar 2003
Posts: 2040
Location: Melbourne, Australia

PeterPotkay wrote:
... as a queue manager can only have one DLQ.

Yes, but DLQ handler rules can detect and move messages to separate application related queues, where they can be dealt with by the relevant app support teams. You could put ".DEAD" on the end of the queue names, to make their purpose quite clear. If the DLQ header is retained, the app team can run their own DLQ handler to attempt redelivery to the original destination queue / qmgr.
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Glenn
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hughson
PostPosted: Tue Oct 29, 2019 6:17 pm Post subject: Reply with quote

Grand Master

Joined: 09 May 2013
Posts: 1283
Location: Bay of Plenty, New Zealand

gbaddeley wrote:
PeterPotkay wrote:
... as a queue manager can only have one DLQ.

Yes, but DLQ handler rules can detect and move messages to separate application related queues, where they can be dealt with by the relevant app support teams. You could put ".DEAD" on the end of the queue names, to make their purpose quite clear. If the DLQ header is retained, the app team can run their own DLQ handler to attempt redelivery to the original destination queue / qmgr.

That doesn't help when the 'application' failing the delivery is the pub/sub engine though. It doesn't have the ability to put the failing publication message onto anything other than the queue manager's Dead Letter queue (singular).

Cheers,
Morag
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gbaddeley
PostPosted: Wed Oct 30, 2019 2:50 pm Post subject: Reply with quote

Jedi

Joined: 25 Mar 2003
Posts: 2040
Location: Melbourne, Australia

hughson wrote:
That doesn't help when the 'application' failing the delivery is the pub/sub engine though. It doesn't have the ability to put the failing publication message onto anything other than the queue manager's Dead Letter queue (singular).
Cheers,
Morag

I was suggesting that runmqdlq would be running against the qmgr's DLQ, and move the failed publications messages to another queue, to separate them from other msgs going thru the DLQ.
Glenn.
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hughson
PostPosted: Wed Oct 30, 2019 7:14 pm Post subject: Reply with quote

Grand Master

Joined: 09 May 2013
Posts: 1283
Location: Bay of Plenty, New Zealand

gbaddeley wrote:
hughson wrote:
That doesn't help when the 'application' failing the delivery is the pub/sub engine though. It doesn't have the ability to put the failing publication message onto anything other than the queue manager's Dead Letter queue (singular).
Cheers,
Morag

I was suggesting that runmqdlq would be running against the qmgr's DLQ, and move the failed publications messages to another queue, to separate them from other msgs going thru the DLQ.
Glenn.

Thanks for clarifying, I didn't glean that from your initial response.

Cheers,
Morag
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