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| Using the MQI from RPG and message size limits |
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| zpat |
 Posted: Tue May 05, 2009 12:10 am Post subject: Using the MQI from RPG and message size limits |
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Jedi Council
Joined: 19 May 2001
Posts: 5866
Location: UK
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One of our RPG (AS/400) programmers tells me that a single RPG variable has a max size of 64kb.
What is the recommended way to MQGET a MQ message longer than 64 KB in RPG (e.g. 4 MB)?
Presumably using an array or structure - can someone please clarify this? |
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| rtsujimoto |
| Posted: Tue May 05, 2009 7:58 am Post subject: |
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Centurion
Joined: 16 Jun 2004
Posts: 119
Location: Lake Success, NY
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Here's an old posting that discusses this:
Hi all,
Of course it's possible to use larger fields than 32k in ILE/RPG. You must
use a trick that might not be known to everyone. The trick is to create an
array that is large enough to hold the data. In the sample that i attach
with my reply the array can hold messages up to 4Mb. The sample also
include a call to a c function (memmove) that make it easier to manipulate
the data in the large array. The sample is not complete. It has been
taken out of a larger program that act as a standard MQ adapter in our
back end systems.
contact admin Nyberg
Electrolux IT Solutions - Sweden
Nick Denning <nick.denning@STRATEGICTHOUGHT.CO.UK> wrote:
>Guys,
>
>Potentially a neat way to help address this might be to specify the maximum
>message length for the queue to be 32k (or indeed what ever the maximum
>length is that you wish to deal with). If you then set the message to
>segment if necessary on MQPUT and MQGET to wait until all segments are
>available, but still only dequeue them manually then you probably get the
>best of all worlds:
>
>Minimim complexity in any applications writing to the queue outside RPG as
>the segmentation is done for you, minimum complexity in the applications
>reading from the queue that are not written in RPG as they can use the
>automatic assembly mechanism, but scope for the RPG program to retrieve each
>of the segments separately as Rakesh has described below.
>
>I have code that does all this:
>
>Put a message that segments itself if required:
>
> pMsgDesc->MsgFlags |= MQMF_SEGMENTATION_ALLOWED;
> pMsgDesc->Version = MQMD_VERSION_2;
>
>put a specific segment:
>
> pMsgDesc->MsgFlags = MQMF_SEGMENT;
> pMsgDesc->Version = MQMD_VERSION_2;
>
>put the last segment:
>
> pMsgDesc->Version = MQMD_VERSION_2;
> pMsgDesc->MsgFlags = MQMF_LAST_SEGMENT;
>
>
>Get a segmented message in one go:
>
> pGetMsgOpts->Options |= MQGMO_COMPLETE_MSG;
> pMsgDesc->Version = MQMD_VERSION_2;
>
>Retrieve a segmented message in individual segments:
>
> GetMsgOpts.Options |= MQGMO_ALL_SEGMENTS_AVAILABLE | MQGMO_LOGICAL_ORDER;
> MsgDesc.Version = MQMD_VERSION_2;
> GetMsgOpts.Version = MQGMO_VERSION_2;
>
> while ( GetMsgOpts.SegmentStatus == MQSS_SEGMENT )
>
>Alternatively you have the logical order thing that you can play. Sorry I
>am a C programmer so you will have to find the equivalent in RPG. However
>its pretty straight forward and took me only about half a day to get working
>from the manuals.
>
>nick
>
>-----Original Message-----
>From: Rakesh Jaiswal [mailto:rakesh.jaiswal@WIPRO.COM]
>Sent: 05 April 2002 07:10
>To: MQSERIES@AKH-Wien.AC.AT
>Subject: Re: RPG, AS/400, and mqget
>
>
>Even i am not RPG programmer but I am handling MQ on AS/400 .One of my
>colleague told that it is RPG Language limitation .it is not at all MQ
>limitation. In ILE-RPG Programming language a variable can store max 32k
>byte only.
>We are also facing one problem due to same. When we are transfering image
>file bytes(>32K) then a RPG program that is getting this message is not
>able to receive it in a variable & store in DB2. Now i am trying to send
>data in segments with each segment less then 32k.
>one guy told me that IFS can handle it but couldn't got much info about it.
>If any RGP programmers know how to handle >32k data pls give me some clue.
>
>Regards,
>Rakesh
>
>----- Original Message -----
>From: "Stefan Sievert" <stefansievert@HOTMAIL.COM>
>To: <MQSERIES@AKH-WIEN.AC.AT>
>Sent: Friday, April 05, 2002 2:51 AM
>Subject: Re: RPG, AS/400, and mqget
>
>
>> Andy,
>> I am not experienced with programming on the AS/400, but your question
>made
>> me curious, because that sounds like a limitation that would be too
>> restrictive; so I read the MQSeries for AS/400 APR manual. On the
>> description of the MQGET call (the BUFLEN parameter) it says:
>>
| Quote: |
>> Note: The length of the longest message that it is possible to read from
>the
>> queue is given by the MaxMsgLength local queue attribute
>> |
>> There is no mention of any 32K limit that would apply. However, Usage note
>8
>> states:
>>
| Quote: |
>> The BUFFER parameter shown in the RPG programming example is declared as
>> a string; this restricts the maximum length of the parameter to 256 bytes.
>> If a larger buffer is required, the parameter should be declared instead
>as
>> a structure, or as a field in a physical file.
>> Declaring the parameter as a structure increases the maximum length
>possible
>> to 9999 bytes, while declaring the parameter as a field in a physical file
>> increases the maximum length possible to approximately 32K bytes.
>> |
>> These two statements seem to be contradictory to me, but I am not sure if
>> the latter only refers to the specific implementation of the programming
>> example.
>> Has your developer actually tried to retrieve a message larger than 32K
>and,
>> if yes, what happened? Any errors/warnings with associated reason codes?
>> Maybe some more seasoned RPG programmer can comment further.
>> Cheers,
>> Stefan
>>
>>
>> >From: "Saar, Andrew" <ASaar@GAPAC.COM>
>> >Reply-To: MQSeries List <MQSERIES@AKH-Wien.AC.AT>
>> >To: MQSERIES@AKH-Wien.AC.AT
>> >Subject: RPG, AS/400, and mqget
>> >Date: Thu, 4 Apr 2002 14:00:13 -0500
>> >
>> >We have a developer who is working on an AS/400 where we have a 5.1 queue
>> >manager. He is programming in RPG and is trying to do an MQGet from a
>> >local queue. Very basic. The problem is that the messages are about
>> >100-250K. The programmer is telling me that he cannot pull messages that
>> >are larger than 32K because that is the largest his buffer parameter on
>the
>> >MQGet call will go. I don't understand how this can be possible. I
>looked
>> >through the docs and it appears he's right, but I just refuse to believe
>> >that RPG on AS/400 accessing MQ could be so crippled. Can anyone help?
>> >
>> >Thank you,
>> >Andrew
>>
>>
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>
>
>
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*=====================================================================
* Standalone field definitions.
*=====================================================================
D BufLen S 10i 0
D HObj S 10i 0
D MsgLen S 10i 0
D MQOpts S 10i 0
D QMName S 48a
D Rcode S 4s 0
D W0_WaitC DS 2
D W0_Wait 2s 0
D MQReturnCodes DS
* Completion codes
D CompCode 10i 0
D MQCode 10i 0
D OpenCode 10i 0
* Reasons
D ConnReason 10i 0
D MQReason 10i 0
*---------------------------------------------------------------------
* Prototypes for C functions.
*---------------------------------------------------------------------
D memmove pr 8f extproc('memmove')
D Target * options(*string) value
D Source * options(*string) value
D BufferLen 10i 0 value
*=====================================================================
* Buffer declarations.
*=====================================================================
D BufferLenIn S 9 0
D BufferIn S 1024a Dim(4000) Based(PtrBufIn)
D PtrBufIn S *
C Alloc W0_LenIn PtrBufIn
C ExSr MQGetMsg
* Normal application code goes here
* Free the storage used for the communication buffers.
C DeAlloc PtrBufIn
C Eval *InLr = *On
*=====================================================================
* Get message from source queue:
*=====================================================================
C MQGetMsg BegSr
C Eval GMOPT = GMNONE
* Length of buffer available
C Eval BufLen = W0_LenIn
* MsgId and CorrelId are selectors that must be cleared
* to get messages in sequence, and they are set each MQGET
C Eval MDMID = MINONE
C Eval MDCID = CINONE
C CallP MQGET(HConn : Hobj : MQMD : MQGMO :
C BufLen : PtrBufIn : MsgLen : CompCode :
C MQReason)
* Set BUFLEN to what was received
C If MsgLen < BufLen
C Eval BufLen = MsgLen
C Eval BufferLenIn = MsgLen
C EndIf
* Report reason, if any
C Select
C When MQReason = RCNONE
* Specific text for "no more messages"
C When MQReason = RC2033
C Other
* Otherwise say "MQGET ended with reason code ...."
C Eval CName = 'MQGET '
C ExSr PrtErr
C EndSl
C CallP memmove(%addr( MQSLOGBUFF ):
C PtrBufIn:
C 500)
C EndSr |
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| zpat |
| Posted: Tue May 05, 2009 8:55 am Post subject: |
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Jedi Council
Joined: 19 May 2001
Posts: 5866
Location: UK
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| Apparently there are "user space" areas in RPG now which are undefined memory buffers up to 16 MB and this is how to get around it. |
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