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MQSeries.net Forum IndexGeneral IBM MQ SupportOperational note when adjusting queues to topics

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tczielke
PostPosted: Wed Nov 13, 2019 9:57 am Post subject: Operational note when adjusting queues to topics Reply with quote

Sentinel

Joined: 08 Jul 2010
Posts: 849
Location: Illinois, USA

I ran across this MQ behavior and did not see it posted on the internet, so I thought I would post it here in case it helps anyone else out.

Some MQ admins are familiar with the technique of changing a traditional queuing solution to use pub/sub for various reasons. Here are a couple of documented MQ examples of doing this:

Publish your MQ Events -> https://www.ibm.com/developerworks/community/blogs/aimsupport/entry/publish_your_mq_event_messages?lang=en

PUT message queue with duplicate messages -> https://www.ibm.com/support/pages/mq-you-want-put-message-queue-and-you-want-generate-duplicate-messages-other-queues

I followed these examples and did something similar with MQ Accounting.

One subtlety that I ran across with these documented approaches is that the DEFINE TOPIC does not specify the USEDLQ attribute. On a standard queue manager, this means the USEDLQ for the topic defaults to USEDLQ(ASPARENT) which eventually inherits the value of USEDLQ(YES). This means that when your local queue gets filled up for some reason, MQ will start putting these local PUTs on the DLQ! In my case, you now have accounting data filling your DLQ (which could easily be MAXDEPTH(999999999) and potentially filling your MQ /var/mqm filesystem!). Thankfully, I caught and corrected it before that happened.

Probably, what would be better with these documented solutions is to add USEDLQ(NO) to the DEFINE TOPIC statements.
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hughson
PostPosted: Wed Nov 13, 2019 2:14 pm Post subject: Re: Operational note when adjusting queues to topics Reply with quote

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

tczielke wrote:
Publish your MQ Events -> https://www.ibm.com/developerworks/community/blogs/aimsupport/entry/publish_your_mq_event_messages?lang=en

One subtlety that I ran across with these documented approaches is that the DEFINE TOPIC does not specify the USEDLQ attribute.

Probably, what would be better with these documented solutions is to add USEDLQ(NO) to the DEFINE TOPIC statements.


The "Publish your MQ Events" blog post was written before USEDLQ existed. It is also on a platform that will be sunset at the end of 2019. I am working through the posts that I wrote that are being sunset and moving them to a blog hosting platform that I control. I will move this one, and in the process, I will add USEDLQ as an option.

I have made a note to post back here when I have moved it.

Cheers,
Morag
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tczielke
PostPosted: Thu Nov 14, 2019 4:54 am Post subject: Reply with quote

Sentinel

Joined: 08 Jul 2010
Posts: 849
Location: Illinois, USA

Thank you for the information and working to improve the documentation on your side!
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hughson
PostPosted: Sun Dec 01, 2019 8:13 pm Post subject: Reply with quote

Grand Master

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

Please note, a saved version of the blog post mentioned (which will be sunset soon), can now be found at Publish your MQ Event Messages

I have updated the post to use USEDLQ(NO) in the definitions, and added a little mention below of why you might want that.

Cheers,
Morag
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