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| Why can a message be read two times ? |
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| tniuxs |
 Posted: Mon Jul 19, 2004 4:38 am Post subject: Why can a message be read two times ? |
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Newbie
Joined: 19 Jul 2004
Posts: 2
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Hello,
I'm working with a MDB deployed on a few instances of Weblogic and reading messages from a distant queue manager. Each message triggers a specific treatment.
As I can't use the XAConnection, I can't use the "exactly once" quality of service. If I use "at least once" I'd like to know what can cause a message to be treated 2 times (or more).
I want to understand the mechanism to plot the risks, and know when to look for a duplicated treatment.
For specific reasons (such as licence budget) I can't have a local queue manager on the same machine as the Weblogic server.
Thanks a lot for any help,
Tniuxs |
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| jefflowrey |
| Posted: Mon Jul 19, 2004 4:54 am Post subject: |
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Grand Poobah
Joined: 16 Oct 2002
Posts: 19981
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Messages can be rolled back onto the input queue if an error occurs. This can cause a message to be seen twice by your application.
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I am *not* the model of the modern major general. |
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| PeterPotkay |
| Posted: Mon Jul 19, 2004 10:22 am Post subject: |
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Poobah
Joined: 15 May 2001
Posts: 7722
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If you check out the MQMD_Backoutcount on every MQGET, you can tell if this is the first time any app is getting this exact message, or if it has been rolled back to the queue x times.
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Peter Potkay
Keep Calm and MQ On |
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| bower5932 |
| Posted: Mon Jul 19, 2004 12:01 pm Post subject: |
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Jedi Knight
Joined: 27 Aug 2001
Posts: 3023
Location: Dallas, TX, USA
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| You can use the Message.getJMSRedelivered() to see if a message is being redelivered. |
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| tniuxs |
| Posted: Tue Jul 20, 2004 1:22 am Post subject: |
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Newbie
Joined: 19 Jul 2004
Posts: 2
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Thanks for all that info !
I'd like to know when a "at least once" QOS can differ from a "exactly once" QOS. I need to explain what mechanism can make one act different from the other.
For all I know, in both cases an error causes a roll-back for MQ, and so the message is redeliverd, until the transaction is acted.
With all you gave, I can monitor the duplicate delivery, but I don't understand what the QOS changes, and why there could be trouble in not using XA connectionFactory.
Thanks again,
Tniuxs |
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