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| dead queue vs message retry exits |
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| jim |
 Posted: Thu Apr 10, 2014 10:36 pm Post subject: dead queue vs message retry exits |
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Voyager
Joined: 26 Nov 2013
Posts: 94
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Can we use message retry exits in place of dead letter queue.
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| MQsysprog |
| Posted: Thu Apr 10, 2014 11:18 pm Post subject: |
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Centurion
Joined: 24 Feb 2014
Posts: 116
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Well the dlq is a feature of MQ and a vital component in the ''guaranteed delivery '' messaging concept ,so why don't use it with a good dlq handler to requeue the messages to their appropriate destinations when necessary ?
Probably a message exits may be usefuly when you have to deal with particular types of message handling ,but again
the decision to use exits is driven mainly by the design requirements of applications and their enviroment . |
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| exerk |
| Posted: Fri Apr 11, 2014 12:19 am Post subject: |
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Jedi Council
Joined: 02 Nov 2006
Posts: 6339
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| MQsysprog wrote: |
| ...''guaranteed delivery''... |
Assured once, and once only, delivery - it is not guaranteed and I do wish that that perception would disappear...
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| smdavies99 |
| Posted: Fri Apr 11, 2014 2:20 am Post subject: |
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Jedi Council
Joined: 10 Feb 2003
Posts: 6076
Location: Somewhere over the Rainbow this side of Never-never land.
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There are some sites where DLQ's are forbidden.
I was working at one for a time. We has an app failure and the input queue quickly filled up. some consultant said, you will never need space for more than 1000 messages on any queue.
The resulting disaster took days to sort out. I left soon after (contract ended).
It was not nice.
Really think hard about NOT having a DLQ as a backstop.
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WMQ User since 1999
MQSI/WBI/WMB/'Thingy' User since 2002
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Every time you reinvent the wheel the more square it gets (anon). If in doubt think and investigate before you ask silly questions. |
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| PaulClarke |
| Posted: Fri Apr 11, 2014 3:22 am Post subject: |
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Grand Master
Joined: 17 Nov 2005
Posts: 1002
Location: New Zealand
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The problem with Message Retry exits is that it holds up the whole channel. In other words, all the messages destined to go down that channel are queued up behind the one message that is having trouble. Message Retry exits can be useful to try a very quick retry or alternative location but, in my view, you should retry more than a very few number of seconds. If the bottleneck is not cleared within that time then I think you need a strong reason not to use a DLQ.
The main objection I've seen to having a DLQ is that it can/will cause messages to get out of order. In my view that is just encouraging lazy programming. If an application needs to send a 'batch' of messages then that application should ensure that it gets all the messages and processes them in the right order. Whether it uses MQ concepts like message grouping or its own techniques it does really matter - what it should not rely on is that the messages always arrive in exactly the same order as they were put. All manner of things can happen to a message as it traverses an enterprise, one can not rely on the fact that it will make it to the intended target.
Cheers,
Paul.
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Paul Clarke
MQGem Software
www.mqgem.com |
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| bruce2359 |
| Posted: Fri Apr 11, 2014 7:15 am Post subject: |
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Poobah
Joined: 05 Jan 2008
Posts: 9469
Location: US: west coast, almost. Otherwise, enroute.
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WMQ assures message delivery - once and once-only delivery, with no loss or duplication of messages (by WMQ components).
WMQ cannot guarantee delivery to a specifically named destination queue... if the queue doesn't exist, for example; or if the queue is full, or is put-inhibited, or the message is too big for the queue, or ... Similarly, the US Postal Service cannot guarantee letter or package delivery to a non-existent address. It can return the item to the sender, or notify the sender of the exceptional condition that caused the delivery failure. WMQ offers these same, and other, capabilities.
Folks new to WMQ see the DLQ as the final dump for messages that couldn't be delivered. For most WMQ apps it is not.
IBM supplies a dead-letter queue handler application that allows system administrators to create a pattern-matching rules table that can retry moving the message to its original destination queue, or move a message to another queue for other processing. The dead-letter queue handler app is well documented.
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