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| giriraj.sharma |
 Posted: Tue Jul 31, 2012 11:11 pm Post subject: Backout queue vs Dead letter queue |
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Newbie
Joined: 23 Jul 2012
Posts: 7
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Hi,
Can anyone please explain the exact difference between BACKOUT QUEUE and DEAD LETTER QUEUE?
In detail.
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Giriraj Sharma |
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| fjb_saper |
| Posted: Tue Jul 31, 2012 11:31 pm Post subject: |
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Grand High Poobah
Joined: 18 Nov 2003
Posts: 20756
Location: LI,NY
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Messages in the DLQ should only have been put there by the qmgr and always have the DL header.
Messages on a backout queue are put there by an application (ex JMS) and do not have a DLH... 
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| wmc27 |
| Posted: Wed Aug 01, 2012 5:39 am Post subject: |
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Apprentice
Joined: 18 Dec 2008
Posts: 31
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Is it mandatory to have the Back Out Q for application ?
Thx
S |
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| Vitor |
| Posted: Wed Aug 01, 2012 5:48 am Post subject: |
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Grand High Poobah
Joined: 11 Nov 2005
Posts: 26093
Location: Texas, USA
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| wmc27 wrote: |
| Is it mandatory to have the Back Out Q for application ? |
No. It's acceptable not to have one & WMQ does not enforce their use. Indeed even if present it's the application's responsibility to actually use it (though containers such as WAS offer asistance with this).
Note that without a backout queue or backout handling nothing inside the software will complain, or warn you that in the event of a problem your application will spin round and round burning CPU until someone cancels it.
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Honesty is the best policy.
Insanity is the best defence. |
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| mqjeff |
| Posted: Wed Aug 01, 2012 5:51 am Post subject: |
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Grand Master
Joined: 25 Jun 2008
Posts: 17447
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| Ask your MQ administrator. |
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| lancelotlinc |
| Posted: Wed Aug 01, 2012 5:51 am Post subject: |
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Jedi Knight
Joined: 22 Mar 2010
Posts: 4941
Location: Bloomington, IL USA
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| wmc27 |
| Posted: Wed Aug 01, 2012 6:09 am Post subject: |
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Apprentice
Joined: 18 Dec 2008
Posts: 31
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If you dont have the application back out q and due to some reason the DLQ is filled up with messages,
How do you process those messages that are in DLQ Q
Option A :delete the messages that are in DLQ
Option B :Put them back on the main Q for processing. |
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| mqjeff |
| Posted: Wed Aug 01, 2012 6:23 am Post subject: |
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Grand Master
Joined: 25 Jun 2008
Posts: 17447
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This isn't a Broker issue.
This is a basic MQ training issue.
There is exactly one way to process any message on any queue. You GET it.
Everything else is specific to the contents of the message and the business context the messages exist within.
There are many good reasons for using backout queues. There are at least a few reasons for NOT using backout queues.
This is a decision that should have already been made by a more experienced person at your shop. You should be talking to them.
There's also been a fair amount of discussion on this here. You should spend some time READING and SEARCHING and THINKING. |
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| yellowbee |
| Posted: Wed Aug 01, 2012 6:55 am Post subject: |
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Acolyte
Joined: 14 Apr 2012
Posts: 58
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Dead letter queue is queue manager attribute.What ever the undelivered messages are placed in the Dead letter queue..
Back out queue is a Local queue attribute,We specify the Back out queue in the properties of local queue.If we specify the Back out queue,what ever the undelivered messages to the particular Local queue are sent to the Back out Queue. |
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| zpat |
| Posted: Wed Aug 01, 2012 7:27 am Post subject: |
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Jedi Council
Joined: 19 May 2001
Posts: 5866
Location: UK
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WMB will use the system DLQ if there is no backout queue attribute value in the flow's input queue - and a need arises to reject a message (e.g. the backout count threshold has been exceeded).
Generally better to use explicit queues for WMB's message backout and avoid the system DLQ being used.
The only use of the DLQ by MQ itself that I know of is by the channel agent when it can't put messages to the target queue. |
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| lancelotlinc |
| Posted: Wed Aug 01, 2012 7:38 am Post subject: |
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Jedi Knight
Joined: 22 Mar 2010
Posts: 4941
Location: Bloomington, IL USA
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| zpat wrote: |
WMB will use the system DLQ if there is no backout queue attribute value in the flow's input queue - and a need arises to reject a message (e.g. the backout count threshold has been exceeded).
Generally better to use explicit queues for WMB's message backout and avoid the system DLQ being used.
The only use of the DLQ by MQ itself that I know of is by the channel agent when it can't put messages to the target queue. |
WMB has no attribute on MQInput nodes called "Backout Queue". This is not a WMB function. The queue attribute is defined by WMQ not WMB.
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| mqjeff |
| Posted: Wed Aug 01, 2012 7:41 am Post subject: |
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Grand Master
Joined: 25 Jun 2008
Posts: 17447
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| lancelotlinc wrote: |
| WMB has no attribute on MQInput nodes called "Backout Queue". This is not a WMB function. The queue attribute is defined by WMQ not WMB. |
The internal functions of the MQInput node will honor the BOTHRESH and BOQUEUE of the queue that is being read.
The queue manager does not provide any function to automatically honor those settings, merely to actually set them.
Whether to define a DLQ or not, and whether to define a BOTHRESH and a BOQUEUE or not is a design decision that should be made in consultation with the senior architects and the MQ administration team. |
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| zpat |
| Posted: Wed Aug 01, 2012 8:13 am Post subject: |
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Jedi Council
Joined: 19 May 2001
Posts: 5866
Location: UK
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It's a WMQ queue attribute.
It's acted upon by WMB.
WMQ, contrary to popular belief, does not move messages to backout queues - these queue values are merely ornaments to be enquired upon by applications and acted upon by the applications if they so choose. |
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| smdavies99 |
| Posted: Wed Aug 01, 2012 8:47 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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I know of several financial Instutions (don;t ask for their names) where the use of a DLQ is FORBIDDEN. They'd rather have a channel blocked by an orphan message than have it go to a DLQ.
Why?
Well in these cases the order of processing messages is vital to the application. A management nightmare indeed.
If you decide against using DLQ's in your network then remote messages arriving on your QM without a valid destination queue (ie it does not exist)
For example
Sent to RQM1:APP.In
when it should be
RQM1:APP.IN
will lead to problems.
As has been said, this is all basic WMQ System design.
If you don't believe me then try it out. It will be a useful learning expereince for you.
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| bruce2359 |
| Posted: Wed Aug 01, 2012 9:59 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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| yellowbee wrote: |
Dead letter queue is queue manager attribute.What ever the undelivered messages are placed in the Dead letter queue..
Back out queue is a Local queue attribute,We specify the Back out queue in the properties of local queue.If we specify the Back out queue,what ever the undelivered messages to the particular Local queue are sent to the Back out Queue. |
Please be precise.
The use of a Backout Queue is an application programming issue. The application must decide which message to backout, inquire on the Backout Requeue Queue Name, open the queue, and put the offending message in that queue.
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