| Author |
Message
|
| URPradhan |
 Posted: Sat May 14, 2011 4:35 am Post subject: Set MessageID and CorrelationID |
 |
|
Novice
Joined: 05 May 2011
Posts: 14
|
Hi Friends
Again another question from a beginner.
I'm only sending messages to a queue and I need to set a "user defined" message id+correlation id each time to the messages before sending. The ImqMessage has inherited member functions to do the same, which require an object of ImqBinary. Now, How to create an object of ImqBinary with my user defined message id ?
Thank you. |
|
| Back to top |
|
 |
| fjb_saper |
| Posted: Sat May 14, 2011 5:49 am Post subject: Re: Set MessageID and CorrelationID |
|
|
Grand High Poobah
Joined: 18 Nov 2003
Posts: 20756
Location: LI,NY
|
| URPradhan wrote: |
Hi Friends
Again another question from a beginner.
I'm only sending messages to a queue and I need to set a "user defined" message id+correlation id each time to the messages before sending. The ImqMessage has inherited member functions to do the same, which require an object of ImqBinary. Now, How to create an object of ImqBinary with my user defined message id ?
Thank you. |
There is no harm in being a beginner. This said, best practice tells you that it is a really bad idea to have a user defined message Id. The pattern you want to look up here is "anonymous identifier". This means you let the system create the Id for you. You can then use the Id to identify the message, but you'll only know the Id after the message has been put to the queue. The same goes for creating a correlation Id. The system will also ensure that the values created are unique. You may use the messageId as correlationId, or just pass through and existing correlationId.
Now if you explain more about your requirement, maybe we can give you some way to work it right. In general, I would push back on a request for a user defined messageId or correlationId. If it needs logic, this should have been packed either into the message body, or its user defined properties (as opposed to system defined properties).
Have fun 
_________________
MQ & Broker admin |
|
| Back to top |
|
|
| URPradhan |
| Posted: Sun May 15, 2011 10:15 pm Post subject: |
|
|
Novice
Joined: 05 May 2011
Posts: 14
|
OK. Lets keep aside the MessageID.
What about the Correlation ID ? Hope we can set it to any value for example: 1000 (decimal number). Now how to set this number as correlation id ? |
|
| Back to top |
|
|
| bruce2359 |
| Posted: Mon May 16, 2011 4:54 am Post subject: |
|
|
Poobah
Joined: 05 Jan 2008
Posts: 9469
Location: US: west coast, almost. Otherwise, enroute.
|
Search google for 'imqbinary' or 'imqbinary+example' or 'imqbinary+sample' or you could refer to the WMQ Using c++ manual.
_________________
I like deadlines. I like to wave as they pass by.
ב''ה
Lex Orandi, Lex Credendi, Lex Vivendi. As we Worship, So we Believe, So we Live. |
|
| Back to top |
|
|
| mqjeff |
| Posted: Mon May 16, 2011 7:09 am Post subject: |
|
|
Grand Master
Joined: 25 Jun 2008
Posts: 17447
|
Or simply STOP trying to use the C++ APIs for MQ.
There's no specific reason to use them unless you happen to WANT to, and no specific reason to go to great lengths to make them do things that it's a lot easier to do in the plain MQ API.
And there's absolutely no requirement to use C++ APIs from a C++ program. |
|
| Back to top |
|
|
| gbaddeley |
| Posted: Mon May 16, 2011 3:48 pm Post subject: |
|
|
Jedi Knight
Joined: 25 Mar 2003
Posts: 2538
Location: Melbourne, Australia
|
| URPradhan wrote: |
OK. Lets keep aside the MessageID.
What about the Correlation ID ? Hope we can set it to any value for example: 1000 (decimal number). Now how to set this number as correlation id ? |
You can set CorrelId to any value you like, MQ does not care. Use the normal programming techniques for moving a typed variable to an array of 24 bytes, with padding if required.
Remember to consider processor architectures. Storing an integer in CorrelId on one platform may not be compatible with another platform. eg. Intel to/from just about everything else.
_________________
Glenn |
|
| Back to top |
|
|
| mvic |
| Posted: Mon May 16, 2011 4:32 pm Post subject: |
|
|
Jedi
Joined: 09 Mar 2004
Posts: 2080
|
| gbaddeley wrote: |
| Remember to consider processor architectures. Storing an integer in CorrelId on one platform may not be compatible with another platform. |
You only need to "remember" this if you are treating your MsgId or CorrelId unusually - eg. storing integer values in them.
(Though I concede that, in answer to the question asked, this is reasonable advice).
IMHO, by far the best approach is to let MQ generate MsgId and CorrelId automatically for you, and treat them as opaque "blobs" of data. |
|
| Back to top |
|
|
| URPradhan |
| Posted: Mon May 16, 2011 5:12 pm Post subject: |
|
|
Novice
Joined: 05 May 2011
Posts: 14
|
Actually, as we know the transmission of mq messages happen in asynchronous mode.
But the requirement is that, the messages MUST be read from queue as the order they have been sent.
So to ensure the proper order of message while reading from queue, we are banking upon the CorrelationID, which will be set with an incremental sequence number and the target application will pick-up the messages with next higher CorrelationID exist on the queue.
Does MQ series guaranty the order of the message delivery?
In other words, does it guaranty the FIFO delivery?
Again the target application MUST read the messages in order.
If so then we can remove the dependency to use a correlationid. |
|
| Back to top |
|
|
| bruce2359 |
| Posted: Mon May 16, 2011 5:49 pm Post subject: |
|
|
Poobah
Joined: 05 Jan 2008
Posts: 9469
Location: US: west coast, almost. Otherwise, enroute.
|
| URPradhan wrote: |
Does MQ series guaranty the order of the message delivery?
|
Yes, and no; it depends.
This subject is well documented in the WMQ Application Programming Guide.
Please do some research.
_________________
I like deadlines. I like to wave as they pass by.
ב''ה
Lex Orandi, Lex Credendi, Lex Vivendi. As we Worship, So we Believe, So we Live. |
|
| Back to top |
|
|
| URPradhan |
| Posted: Tue May 17, 2011 2:11 am Post subject: |
|
|
Novice
Joined: 05 May 2011
Posts: 14
|
| bruce2359 wrote: |
| URPradhan wrote: |
Does MQ series guaranty the order of the message delivery?
|
Yes, and no; it depends.
This subject is well documented in the WMQ Application Programming Guide.
Please do some research. |
Thank you for your help.
But after reading the relevant section in the programming guide, I understood is that the safer way to ensure proper order is to include a SEQUENCE number in the message body. And for my application I'm doing the same but setting the CorrelationId from the sequence number.
My sequence number is a 32-bit unsigned integer which would be max 10 char length. But CorrelationId is a 24 char length array. So I have to pad the leading zeros to the sequence number. Hope I'm on right path  |
|
| Back to top |
|
|
| mvic |
| Posted: Tue May 17, 2011 2:27 am Post subject: |
|
|
Jedi
Joined: 09 Mar 2004
Posts: 2080
|
| URPradhan wrote: |
| My sequence number is a 32-bit unsigned integer which would be max 10 char length. But CorrelationId is a 24 char length array. So I have to pad the leading zeros to the sequence number. Hope I'm on right path |
Sounds reasonable.
MQ can give you message ordering, but you have to be careful to implement your qmgr and channels correctly - eg. no dead letter queues allowed, no parallel paths in the topology. With get-by-correlid (assuming I understood your description correctly) you can obtain the assurance you need in the application, and save the need to be so careful in qmgr and channels implementation.
The only downside is that performance of get-by-correlid is a little less than the performance of a simple get. But it is not much less.
As to what you put in the MQMD.Correlid, it's entirely up to you. You appear to suggest encoding your sequence number in text (ASCII).. this will help avoid any integer encoding issues (Big Endian / Little Endian) that were referred-to earlier.
Hope it goes well. |
|
| Back to top |
|
|
| rekarm01 |
| Posted: Tue May 17, 2011 3:06 pm Post subject: Re: Set MessageID and CorrelationID |
|
|
Grand Master
Joined: 25 Jun 2008
Posts: 1415
|
| URPradhan wrote: |
| But CorrelationId is a 24 char length array. |
Actually, CorrelationId is a 24-byte array. |
|
| Back to top |
|
|
| fjb_saper |
| Posted: Tue May 17, 2011 8:12 pm Post subject: |
|
|
Grand High Poobah
Joined: 18 Nov 2003
Posts: 20756
Location: LI,NY
|
| Quote: |
| As to what you put in the MQMD.Correlid, it's entirely up to you. You appear to suggest encoding your sequence number in text (ASCII).. this will help avoid any integer encoding issues (Big Endian / Little Endian) that were referred-to earlier. |
But it raises other concerns as the correlId is a byte array and even if the content is text it NEVER gets translated from one CCSID to another.
_________________
MQ & Broker admin |
|
| Back to top |
|
|
| gbaddeley |
| Posted: Thu May 19, 2011 5:16 pm Post subject: |
|
|
Jedi Knight
Joined: 25 Mar 2003
Posts: 2538
Location: Melbourne, Australia
|
| URPradhan wrote: |
Actually, as we know the transmission of mq messages happen in asynchronous mode.
But the requirement is that, the messages MUST be read from queue as the order they have been sent.
So to ensure the proper order of message while reading from queue, we are banking upon the CorrelationID, which will be set with an incremental sequence number and the target application will pick-up the messages with next higher CorrelationID exist on the queue. |
That technique will work, but use a WaitInterval on MQGET, and cater for the possibility that messages might be missing or out of sequence. A suggestion is that the app should keep a table of missing message sequence numbers and periodically try to get them.
| Quote: |
Does MQ series guaranty the order of the message delivery?
In other words, does it guaranty the FIFO delivery? |
No.
_________________
Glenn |
|
| Back to top |
|
|
| PeterPotkay |
| Posted: Fri May 20, 2011 3:53 am Post subject: |
|
|
Poobah
Joined: 15 May 2001
Posts: 7722
|
| gbaddeley wrote: |
| and cater for the possibility that messages might be missing or out of sequence. |
or duplicate messages (duplicated by the sending app for whatever reason)
| gbaddeley wrote: |
| Quote: |
Does MQ series guaranty the order of the message delivery?
In other words, does it guaranty the FIFO delivery? |
No. |
It does when certain, rather restrictive and not necessarily wise conditions are met.
_________________
Peter Potkay
Keep Calm and MQ On |
|
| Back to top |
|
|
|
|
