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| Msg priority and channel xmit queue |
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| mqnomad |
 Posted: Mon Apr 19, 2010 12:53 pm Post subject: Msg priority and channel xmit queue |
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Acolyte
Joined: 18 Mar 2010
Posts: 53
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As far as the messages picked off a xmit queue - is my understanding correct that the channel MSGDLVSQ will dictate if FIFO within prio, or just FIFO is used to get messages from the channel? So - specifying FIFO in this value will negate priority - is this correct?
According to the doc:
"
MSGDLVSQ Message delivery sequence. This parameter is supported only on local and model queues.
PRIORITY Messages are delivered (in response to MQGET API calls) in first-in-first-out (FIFO) order within priority.
FIFO Messages are delivered (in response to MQGET API calls) in FIFO order. Priority is ignored for messages on this queue.
If the message delivery sequence is changed from PRIORITY to FIFO while there are messages on the queue, the order of the messages already on the queue is not changed. Messages added to the queue subsequently take the default priority of the queue, and so might be processed before some of the existing messages." |
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| Vitor |
| Posted: Mon Apr 19, 2010 1:49 pm Post subject: Re: Msg priority and channel xmit queue |
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Grand High Poobah
Joined: 11 Nov 2005
Posts: 26093
Location: Texas, USA
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| mqnomad wrote: |
| So - specifying FIFO in this value will negate priority - is this correct? |
Yes. As is says in the link you provide:
| mqnomad wrote: |
| FIFO Messages are delivered (in response to MQGET API calls) in FIFO order. Priority is ignored for messages on this queue. |
In the context of a xmitq the MCA acts like any other application doing a MQGet
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Honesty is the best policy.
Insanity is the best defence. |
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| mqnomad |
| Posted: Mon Apr 19, 2010 2:55 pm Post subject: |
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Acolyte
Joined: 18 Mar 2010
Posts: 53
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| bruce2359 |
| Posted: Mon Apr 19, 2010 4:15 pm Post subject: |
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Poobah
Joined: 05 Jan 2008
Posts: 9472
Location: US: west coast, almost. Otherwise, enroute.
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A warning: MessageDeliverySequence by priority offers some undesirable results, consequences, namely: If messages of high(er) priority continue to arrive in the queue, low(er) priority messages may never be processed. This is not unique to xmit queues.
If you know that some messages are of higher priority (value) need to be transmitted, then create a second channel pair between qmgrs, and have the application MQOPEN a QRemote definition that picks the fast path.
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| mqnomad |
| Posted: Wed Apr 21, 2010 3:40 am Post subject: |
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Acolyte
Joined: 18 Mar 2010
Posts: 53
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| Interesting, thanks. Never heard of this. |
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| bruce2359 |
| Posted: Wed Apr 21, 2010 5:14 am Post subject: |
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Poobah
Joined: 05 Jan 2008
Posts: 9472
Location: US: west coast, almost. Otherwise, enroute.
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When this occurs, it is seen as a performance problem for some applications, but not others.
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Lex Orandi, Lex Credendi, Lex Vivendi. As we Worship, So we Believe, So we Live. |
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