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| Two trigger messages |
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| Nigelg |
 Posted: Fri May 25, 2007 5:10 am Post subject: Two trigger messages |
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Grand Master
Joined: 02 Aug 2004
Posts: 1046
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Does anybody know the meaning of this part of the triggering section of the APG, and the conditions that cause the two trigger msgs to be created? If so, I would be grateful for an explanation...
| Quote: |
| Note: If you stop and restart the queue manager, the TriggerInterval "timer" is reset. There is a small window during which it is possible to produce two trigger messages. The window exists when the queue's trigger attribute is set to enabled at the same time as a message arrives and the queue was not previously empty (MQTT_FIRST) or had TriggerDepth or more messages (MQTT_DEPTH). |
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| tleichen |
| Posted: Fri May 25, 2007 5:50 am Post subject: |
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Yatiri
Joined: 11 Apr 2005
Posts: 663
Location: Center of the USA
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As I recall, the number of trigger messages in not exactly predictable with "trigger on depth" or "trigger on every", but works as expected with "trigger on first". That has been my experience, anyway. 
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| bruce2359 |
| Posted: Fri May 25, 2007 7:25 am Post subject: |
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The point of the doc telling you that it is possible for multiple trigger messages to arive is so that your application programmer will anticipate this.
It is possible, as well, that a triggered instance of the MQGETting application could encounter a rc2033 (no message available) because some other instance of the same (or other) program has already consumed the message.
Triggerins is complicated. There are a variety of reasons that 'triggers go bad.' There are at least a dozen pages in the MQSC, APR and APG manuals, devoted to triggering. Sys admins and programmers need to read and understand triggering. |
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| PeterPotkay |
| Posted: Fri May 25, 2007 5:24 pm Post subject: |
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Poobah
Joined: 15 May 2001
Posts: 7722
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Nigel,
I think it probably covers MQ due to the way its coded under the covers.
Q depth is >0. You turn on triggering at the same time a message arrives.
A. Turning on triggering for a q with > 0 messages will cause a trigger message.
B. A triggered (on first) queue with > 0 will generate a trigger message if a new app message lands on the queue and Trigger Interval has passed (except on z/os, where you don't need another app message, only trig int to pass).
Restarting the QM resets the trigger interval, or if I read between the lines correctly, it tells the QM to assume trigger interval has passed and start counting again.
So if A and B occur at the same time, and B will happen after a QM restart because trigger interval has "passed", both A and B will each produce a trigger message.
This is just an educated guess.
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