Where and what to trace

Trace points are the locations in the application's code where the system will create trace entries. You must decide where these trace points will be. Some choices are:

• Module entry
• Module exit
• Start of a functional request
• Major checkpoints in the process of completing a request
• Completion of a functional request
• Interface to another system function
• Interface to the same application on another system
• Any unusual event, such as a detected I/O error or entry to a recovery routine.

You must also decide what information to record in the trace entries, which can hold a variable amount of data. The following are suggestions on the types of data you might place in the trace entries:

• Identification of the unit of work or transaction that is being serviced by the application. This can be the ASID, JOBNAME, USERID, task control block (TCB), service request block (SRB), or transaction identifier.
• For entries that trace the flow of control, the caller's return address.
• For entries that trace the start of a functional request, the input parameters.
• For internal checkpoints, an identification that ties this trace entry to the original request, and information on the current status of the process.
• For unusual events, the cause of the problem and any additional data. For example, you could record a system completion (abend) code and reason code for entry to a recovery routine.
• On return from a service, the return code and reason code (consider having a separate identifier for recording return codes that indicate errors).
• For trace entries being used for analysis rather than as a debugging aid, whatever information the user of the application needs.