Interpreting the trace information

The GTFTRACE produced by IBM® MQ can be examined to determine possible errors with invalid addresses, invalid control blocks, and invalid data.

When you look at the data produced by the GTFTRACE command, consider the following points:

If the control block consists completely of zeros, it is possible that an error occurred while copying data from the user's address space. This might be because an invalid address was passed.
If the first part of the control block contains non-null data, but the rest consists of zeros, it is again possible that an error occurred while copying data from the user's address space, for example, the control block was not placed entirely within valid storage. This might also be due to the control block not being initialized correctly.
If the error occurred on exit from IBM MQ, it is possible that IBM MQ might not write the data to the user's address space. The data displayed is the version that it was attempting to copy to the user's address space.

The following tables show details of the control blocks that are traced.

Table 1 illustrates which control blocks are traced for different MQI calls.

Table 1. Control blocks traced for IBM MQ MQI calls
MQI call	Entry	Exit
MQCB	MQCBD, MQMD, MQGMO	MQCBD, MQMD, MQGMO
MQCLOSE	None	None
MQGET	MQMD, MQGMO	MQMD, MQGMO, and the first 256 bytes of message data
MQINQ	Selectors (if `SelectorCount` is greater than 0)	Selectors (if `SelectorCount` is greater than 0) Integer attributes (if `IntAttrCount` is greater than 0) Character attributes (if `CharAttrLength` is greater than 0)
MQOPEN	MQOD	MQOD
MQPUT	MQMD, MQPMO, and the first 256 bytes of message data	MQMD, MQPMO, and the first 256 bytes of message data
MQPUT1	MQMD, MQOD, MQPMO, and the first 256 bytes of message data	MQMD, MQOD, MQPMO, and the first 256 bytes of message data
MQSET	Selectors (if `SelectorCount` is greater than 0) Integer attributes (if `IntAttrCount` is greater than 0) Character attributes (if `CharAttrLength` is greater than 0)	Selectors (if `SelectorCount` is greater than 0) Integer attributes (if `IntAttrCount` is greater than 0) Character attributes (if `CharAttrLength` is greater than 0)
MQSTAT	MQSTS	MQSTS
MQSUB	MQSD, MQSD.ObjectString, MQSD.SubName, MQSD.SubUserData, MQSD.SelectionString, MQSD.ResObjectString	MQSD, MQSD.ObjectString, MQSD.SubName, MQSD.SubUserData, MQSD.SelectionString, MQSD.ResObjectString
MQSUBRQ	MQSRO	MQSRO

Note: In the special case of an MQGET call with the WAIT option, a double entry is seen if there is no message available at the time of the MQGET request, but a message subsequently becomes available before the expiry of any time interval specified.

This is because, although the application has issued a single MQGET call, the adapter is performing the wait on behalf of the application and when a message becomes available it reissues the call. So in the trace it appears as a second MQGET call.

Information about specific fields of the queue request parameter list is also produced in some circumstances. The fields in this list are identified as follows:

Identifier	Description
Action	Requested action
BufferL	Buffer length
CBD	Address of callback descriptor
CompCode	Completion code
CharAttL	Character attributes length
DataL	Data length
Hobj	Object handle
Hsub	Subscription handle
IntAttC	Count of integer attributes
pObjDesc	Object descriptor
Oper	Operation
Options	Options
pBuffer	Address of buffer
pCharAtt	Address of character attributes
pCTLO	Address of control callback options
pECB	Address of ECB used in get
pGMO	Address of get message options
pIntAtt	Address of integer attributes
pMsgDesc	Address of message descriptor
pPMO	Address of put message options
pSD	Address of subscription descriptor
pSelect	Address of selectors
pSRQOpt	Address of subscription request options
pSTS	Address of status structure
Reason	Reason code
RSVn	Reserved for IBM
SelectC	Selector count
Thread	Thread
Type	Requested type
UOWInfo	Information about the unit of work
Userid	CICS® or IMS user ID, for batch or TSO this is zero