Question

I am trying to receive the message from the queue using ANSI-C and MQGET function. The problem is that I always get error 2010 (MQRC_DATA_LENGTH_ERROR).

I found out that this error concerns parameter 7 of the MQGET call (DataLength). The message on my queue has 7157460 bytes. The channel I am using for MQGET has the “Maximum message length” set to 104857600 (as well as the queue holding the message).

I am even using the MQGET from this example:
http://www.capitalware.biz/dl/code/c/msg2file.zip

And I still end up with error 2010. What am I doing wrong? Should I somehow increase the maximum size of the message in MQSERVER environment variable?

MQGET call:

/* ... */
MQLONG   messlen;            /* message length received       */

MQGET(Hcon,                  /* connection handle                 */
        Hobj,                /* object handle                     */
        &md,                 /* message descriptor                */
        &gmo,                /* get message options               */
        buflen,              /* pBuffer length                    */
        pBuffer,             /* pointer to message buffer         */
        &messlen,            /* message length                    */
        &CompCode,           /* completion code                   */
        &Reason);            /* reason code                       */

Answer 1

I’ve got it! The answer is to use MQCONNX call to connect to queue manager.

Example:

#include <cmqxc.h>
/* ... */
MQCNO   mqcno = {MQCNO_DEFAULT} ; /* Connection options */
MQCD    mqcd  = {MQCD_CLIENT_CONN_DEFAULT};  /* Channel Defs */

/* ... */
mqcd.MaxMsgLength = 104857600L; /* 100 MB */

MQCONNX(mQueueManager.Name,
     &mqcno,
     &mQueueManager.ConnectionHandle,
     &mQueueManager.CompletionCode,
     &mQueueManager.ReasonCode);

It worked like a charm!

But please remember – if you find yourself needing to increase the maximum message size – think twice. There is probably something wrong with the design. In another words – MQ should not be used for transferring big messages. MQ File Transfer Edition is one of the solutions then.