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Generating IBM MQ GTF trace on IBM z/OS

Troubleshooting


Problem

This document details how to generate an IBM MQ GTF trace on IBM z/OS in order to investigate a problem.

Cause

IBM MQ GTF trace can help to determine why a problem is happening, whether the cause of the problem is in IBM MQ itself, an application, the operating system, or the network. Minimize the length of time you trace in order to avoid generating excessively large files or filling up your disk. For other kinds of traces refer to:

Resolving The Problem

Before Tracing

Make sure the following APARs have been applied to WebSphere MQ V7.1, V7.0.1 and V6.0 before tracing. Some supersede additional PTFs for MQ GTF tracing.




Generating an IBM MQ GTF trace


  1. Start GTF.

    • Make sure the trace data set has a primary allocation of at least 200 cylinders. GTF only allocates primary extents, not secondary extents. You may need 1000 or more cylinders depending on processing volumes.

    • You can use the JOBNAME option to limit the jobs whose processing in the MSTR is to be traced. This may include the MSTR, CHIN, batch, CICS, IMS, or TSO job names. Include the jobs that call MQPUT and MQGET. Up to five job names can be listed.

    • You can not route CHIN internal trace entries, which include inbound and outbound data transmissions, to GTF. They only appear in a dump of the CHIN job and CSQXTRDS dataspace.

    • In order to minimize lost events, increase the dispatching priority of the GTF job and increase the size of the GTF buffer. For example, specify a parameter of BLOK=3M when starting GTF. The default is 40K.

    • See the z/OS MVS Diagnosis Tools and Service Aids manual for further details of GTF, such as setting up a catalogued procedure.



      Starting GTF Example


      /START GTFxx.yy,,,(BLOK=3M)

      00 AHL100A SPECIFY TRACE OPTIONS

      /R 00,TRACE=JOBNAMEP,USRP

      01 AHL101A SPECIFY TRACE EVENT KEYWORDS--JOBNAME=,USR=

      /R 01,JOBNAME=(ssidMSTR,ssidCHIN,zzzzzzzz),USR=(5E9,5EA,5EE)

      02 AHL102A CONTINUE TRACE DEFINITION OR REPLY END

      /R 02,END

      03 AHL125A RESPECIFY TRACE OPTIONS OR REPLY U

      /R 03,U

      AHL031I GTF INITIALIZATION COMPLETE



      xx is an optional name of a GTF procedure to use
      yy is an identifier for this occurrence of GTF trace
      ssid is the subsystem id of the queue manager
      zzzzzzzz is an optional jobname



    • Alternatively, you can route GTF trace to an internal buffer rather than to a data set. The GTF information will be included when a dump is taken, which is especially useful in a slip dump. Simply start GTF trace as listed above with addition parameters of MODE=INT and REGION=1000K. Additionally, the GTF parameters SADMP, SDUMP or ABDUMP should be set to at least 10M, depending on the type of dump, for example:


      Routing GTF to an internal buffer


      /START GTFxx.yy,,,(BLOK=3M,MODE=INT,SD=10M,SA=10M,REGION=1000K)



    • The parameters on the START GTF command may need to be specified as overrides for variables, depending on how your GTF procedure is set up.


  2. Start the IBM MQ GTF trace. If you omit this step, the GTF data set will be empty. In this command, /cpf refers to the command prefix for the IBM MQ subsystem:


    Starting IBM MQ GTF trace


    /cpf START TRACE(GLOBAL) DEST(GTF) CLASS(*) RMID(*)



  3. Reproduce the problem while tracing is active, making every attempt to keep the trace as short as possible.


  4. Stop the GTF trace, remembering that yy is the identifier used above for this GTF trace:


    Stopping GTF trace


    /STOP yy



  5. Stop the IBM MQ GTF trace. In this command, /cpf refers to the command prefix for the IBM MQ subsystem:


    Stopping IBM MQ GTF trace


    /cpf STOP TRACE(GLOBAL) DEST(GTF) CLASS(*) RMID(*)



  6. Format the GTF trace and review it.

    • The 5E9 and 5EA GTF event identifiers (EIDs) contain information about control blocks on entry to and return from IBM MQ, respectively.

    • Refer to the links below for information on COPY, header, include and module files, data type descriptions and constant values to interpret this information.

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Additional Information



IBM MQ V8.0

WebSphere MQ V7.1


WebSphere MQ V7.0.1

WebSphere MQ V6.0


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Product Synonym

IBM MQ WebSphere MQ WMQ

Document Information

Modified date:
21 June 2018

UID

swg21665047

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