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MQSeries.net Forum IndexGeneral IBM MQ SupportDuplicate Messages

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kdash
PostPosted: Wed Jul 11, 2001 4:27 am Post subject: Reply with quote

Newbie

Joined: 10 Jul 2001
Posts: 1

Hello all,
I'm wondering if MQSeries comes up with guarantees about possible duplicate messages. I mean is there some mechanisms (and if yes, what are they) that prevents a message to be delivered twice from a given QManager to another remote one (for instance if the link goes down between the two Q managers while the destination one sends an ACK to the sending one, saying "I got your message" -> the sending one might believe the msg has not been delivered, and will try to send it again, thus delivering it twice).
This is a major issue, relative to all financial transactions for example (you certainly don't want your account to be charged twice ).
Someone has any inputs about it ?
Thx !

dash
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kolban
PostPosted: Wed Jul 11, 2001 5:34 am Post subject: Reply with quote

Grand Master

Joined: 22 May 2001
Posts: 1072
Location: Fort Worth, TX, USA

Dash, I am pleased to say that this is basic MQSeries functionality. When a message moves from one queue manager to another it is bracketed by a transactional logical unit of work. It is never deleted from the sending side until after the receiver has issued a positive confirmation that it has arrived and been safely deposited. In the event that the receiver has obtained the message but the network, receiver or sender fail before the confirmation is received then when the channel is restarted, a re-synchronization occurs and the transaction is resolved in the correct fashion. If the receiver did get the message then it will then send a positive ack and the sender will delete it. MQSeries has gone to a lot of trouble to ensure neither lost nor duplicated messages.
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