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MQSeries.net Forum IndexMultiphase CommitDuplicate XID - How long MQ holds on to an XID

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IntegratorWMB
PostPosted: Mon Jan 04, 2010 8:36 am Post subject: Duplicate XID - How long MQ holds on to an XID Reply with quote

Apprentice

Joined: 06 Dec 2007
Posts: 27

I am using a 3rd Party Transaction Manager. Currently this software, creates an unique XID. The software do not generate the same XID and during shutdown it writes in to a file and reads it upon restart.

Deleting this file, results in Duplicate XID for websphere MQ. My question is how does MQ knows the XID is a duplicate one even after the transaction is committed/rolledback.

I assume it holds on to all XID's for a specific period of time. Is my assumption correct?

If so, is there an easy way to set that time period (or) flush all existing XID's from mq server.

Note : I dont have any issues in our production environment.(where the server access is controlled).

I face this issue in my development environment where the head count of developers are high, and deletion of this file results in the problem of duplicate xid. Also, if we use the same XID after a period of time ( say anything above x days (or) so, I dont see the problem). Sometime the x is 5 (or) 6 (or) 7 day(s) and above and its not consistent. Any suggestions?

Thanks for any inputs.
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bruce2359
PostPosted: Mon Jan 04, 2010 8:48 am Post subject: Reply with quote

Poobah

Joined: 05 Jan 2008
Posts: 8576
Location: US: west coast, almost. Otherwise, enroute.

Quote:
Deleting this file, results in Duplicate XID for websphere MQ.

Why would you delete a critical component of WMQ or your 3rd party transaction manager?! What outcome would you expect - other than the one you got?

Quote:
My question is how does MQ knows the XID is a duplicate one even after the transaction is committed/rolledback.

The xid (logical unit of work id) represents messages that are/were part of a UofW that WMQ may need to replay at some point during a backout or restart. Starting a new UofW with a pre-existing id violates the XA protocol. This is working as designed.
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mvic
PostPosted: Mon Jan 04, 2010 8:56 am Post subject: Re: Duplicate XID - How long MQ holds on to an XID Reply with quote

Jedi

Joined: 09 Mar 2004
Posts: 2078

IntegratorWMB wrote:
Deleting this file, results in Duplicate XID for websphere MQ. My question is how does MQ knows the XID is a duplicate one even after the transaction is committed/rolledback.

A qmgr keeps a list of all transactions it needs to know about. If it still knows about one, it must still be in the list so the TM must not yet have told the qmgr it is committed or rolled back.

Quote:
I assume it holds on to all XID's for a specific period of time. Is my assumption correct?

No, the qmgr maintains its knowledge of the transaction as long as this is needed under the XA specification. This could be forever, if your qmgr sits unused forever.

If you restart your qmgr, all transactions that are not committed or prepared (ie. have completed 1st phase of the 2 phase commit) are rolled back.
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