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| Are the msgid's generated by MQ unique? |
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| bpolimera |
 Posted: Tue Jun 17, 2003 7:51 am Post subject: Are the msgid's generated by MQ unique? |
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Novice
Joined: 22 Apr 2002
Posts: 14
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Hi,
I want to know if MQ recycles MSGID's with in a single run and across
multiple runs? By a single run, I mean from QMGR Startup to QMGR shutdown.
And also curious, how MQ generates MSGID's. Does it use current time information to generate MSGID that is unique across time?
I am doing asynchronous messaging and trying to match request and response using msgid/correlid. For this, I need the msgid to be unique, preferably forever.
Thanks in advance,
Balaji. |
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| bower5932 |
| Posted: Tue Jun 17, 2003 9:47 am Post subject: |
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Jedi Knight
Joined: 27 Aug 2001
Posts: 3023
Location: Dallas, TX, USA
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From the Application Programming Reference:
| Quote: |
A MsgId generated by the queue manager consists of a 4-byte product identifier ('AMQb' or 'CSQb' in either ASCII or EBCDIC, where 'b' represents a blank), followed by a product-specific implementation of a unique string. In MQSeries this contains the first 12 characters of the queue-manager name, and a value derived from the system clock. All queue managers that can intercommunicate must therefore have names that differ in the first 12 characters, in order to ensure that message identifiers are unique. The ability to generate a unique string also depends upon the system clock not being changed backward. To eliminate the possibility of a message identifier generated by the queue manager duplicating one generated by the application, the application should avoid generating identifiers with initial characters in the range A through I in ASCII or EBCDIC (X'41' through X'49' and X'C1' through X'C9'. However, the application is not prevented from generating identifiers with initial characters in these ranges. |
As far as uniqueness, it will be unique (unless you happen to have 2 qmgrs that share the 1st 12 characters of their name and put a message at the same point in time). |
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| bpolimera |
| Posted: Tue Jun 17, 2003 12:48 pm Post subject: |
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Novice
Joined: 22 Apr 2002
Posts: 14
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| That clarifies. Thanks very much for your reply. |
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