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MQSeries.net Forum IndexGeneral IBM MQ SupportMQGMO_SYNCPOINT & Segmentation

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Andreano
PostPosted: Tue Jan 08, 2019 4:54 am Post subject: MQGMO_SYNCPOINT & Segmentation Reply with quote

Newbie

Joined: 08 Jan 2019
Posts: 4

Hello, experts.

I using MQ Queue with MQMF_SEGMENTATION_ALLOWED flag for PUT and MQGMO_COMPLETE_MSG flag for GET messages.

Queue MaxMsgLength = 32*1024.
Queue Manager MaxMsgLength = 100*1024*1024
Queue Manager Max Uncommited Messages = 1000

Queue is empty. I PUT message with size = 50*1024*1024, it is OK, i have not an error. I commit this. Then I try get this message with flag MQGMO_SYNCPOINT i get an error MQRC_BACKED_OUT and message remove from queue. If I remove flag MQGMO_SYNCPOINT that's work well! What is the reason?
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PaulClarke
PostPosted: Tue Jan 08, 2019 11:24 am Post subject: Reply with quote

Guardian

Joined: 17 Nov 2005
Posts: 914
Location: New Zealand

What is your value of MAXUMSGS for your Queue Manager ? Putting a 50MB message in 32KB chunks is an awful lot of chunks. Is it possible that you have reached the maximum number of messages per syncpoint for your Queue Manager ?

Cheers,
Paul.
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Paul Clarke
MQGem Software
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bruce2359
PostPosted: Tue Jan 08, 2019 1:16 pm Post subject: Re: MQGMO_SYNCPOINT & Segmentation Reply with quote

Poobah

Joined: 05 Jan 2008
Posts: 8328
Location: US: west coast, almost. Otherwise, enroute.

Andreano wrote:
Hello, experts.

I using MQ Queue with MQMF_SEGMENTATION_ALLOWED flag for PUT and MQGMO_COMPLETE_MSG flag for GET messages.

Queue MaxMsgLength = 32*1024.
Queue Manager MaxMsgLength = 100*1024*1024
Queue Manager Max Uncommited Messages = 1000

Queue is empty. I PUT message with size = 50*1024*1024, it is OK, i have not an error. I commit this. Then I try get this message with flag MQGMO_SYNCPOINT i get an error MQRC_BACKED_OUT and message remove from queue. If I remove flag MQGMO_SYNCPOINT that's work well! What is the reason?

If maxmsglength for the queue is 32K, and you are attempting to put 50M, it will take more than the qmgr 1000 MAXUMSGS. If my basic math skills are still alive, it will take about 1563 MAXUMSGS.

Alter your qmgr MAXUMSGS to 2000, and try again.
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PaulClarke
PostPosted: Tue Jan 08, 2019 2:26 pm Post subject: Reply with quote

Guardian

Joined: 17 Nov 2005
Posts: 914
Location: New Zealand

Ha! Must have been not quite awake this morning. The poster actually posted the value of MAXUMSG and I didn't notice. Kind of odd though - they must have suspected that this was the issue in the first place in order to post the value.

P.
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bruce2359
PostPosted: Tue Jan 08, 2019 4:31 pm Post subject: Reply with quote

Poobah

Joined: 05 Jan 2008
Posts: 8328
Location: US: west coast, almost. Otherwise, enroute.

MAXUMSG sets the maximum number of messages in a unit-of-work by a single application instance.

Sounds to me like a certification or employment question.
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Andreano
PostPosted: Wed Jan 09, 2019 2:29 am Post subject: Reply with quote

Newbie

Joined: 08 Jan 2019
Posts: 4

Thx guys!

bruce2359 wrote:
Alter your qmgr MAXUMSGS to 2000, and try again.

Thank you, but i do not have access for QM settings, therefore I posted here, else i would tried it at first.

PaulClarke wrote:
Ha! Must have been not quite awake this morning. The poster actually posted the value of MAXUMSG and I didn't notice. Kind of odd though - they must have suspected that this was the issue in the first place in order to post the value.
P.

Yes, of course, I suspect it more than others.

bruce2359 wrote:
MAXUMSG sets the maximum number of messages in a unit-of-work by a single application instance

Flag MQGMO_SYNCPOINT tells Queue Manager must started unit-of-work. But why it counts segments? It is one logical message, why it cannot join all parts innerly. It is strange behavior.

bruce2359 wrote:

Sounds to me like a certification or employment question.

Maybe it is newbie question, but exactly not.
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exerk
PostPosted: Wed Jan 09, 2019 3:16 am Post subject: Reply with quote

Jedi Council

Joined: 02 Nov 2006
Posts: 5993

Andreano wrote:
...But why it counts segments? It is one logical message, why it cannot join all parts innerly. It is strange behavior...

Because each segment is a discrete message, and therefore counts toward the MAXUMSG count.

Think of it like a Lego kit - each block (segment) is discrete, and the box (MAXUMSG) it comes in must be big enough to hold all the blocks. If the box is not big enough to hold all the pieces, you'll need a bigger box.
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Andreano
PostPosted: Wed Jan 09, 2019 6:12 am Post subject: Reply with quote

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Joined: 08 Jan 2019
Posts: 4

exerk wrote:
Think of it like a Lego kit



Thank you guys! I guess topic can be closed.
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bruce2359
PostPosted: Wed Jan 09, 2019 8:20 am Post subject: Reply with quote

Poobah

Joined: 05 Jan 2008
Posts: 8328
Location: US: west coast, almost. Otherwise, enroute.

MQ offers a variety of useful configuration options to limit use (abuse) of system resources by misbehaving applications.

Excessive messages in a single unit of work can be constrained by MAXUMSG queue manager attribute.

Excessively large messages can be limited by MAXMSGL queue attribute.

Excessive number of messages can be limited by MAXDEPTH queue attribute.

These are well documented in the IBM official administration and development documents.

We don't close topics here. Rather, we leave them open for the benefit of others.
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bruce2359
PostPosted: Wed Jan 09, 2019 8:50 am Post subject: Reply with quote

Poobah

Joined: 05 Jan 2008
Posts: 8328
Location: US: west coast, almost. Otherwise, enroute.

Andreano wrote:
Flag MQGMO_SYNCPOINT tells Queue Manager must started unit-of-work.

More precisely, MQGMO_SYNCPOINT tells the qmgr that THIS message is to be MQPUT inside a UofW. The developer determines which message, if any, are to be in a UofW.

Andreano wrote:
But why it counts segments? It is one logical message, why it cannot join all parts. It is strange behavior.


The smallest unit of information is a physical message. MQ internals work with physical messages - a single MQPUT or a single MQGET.

Developers can work with logical messages comprised of physical messages with message groups or message segmentation. Each message segment is a physical message. Each message segment is counted in CURDEPTH queue attribute.

Segments are useful when it is necessary to handle messages that are too large for the putting or getting application or too large for the queue or too large for the queue manager.

It is not strange behavior. Message segmentation and message groups are well documented.
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