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Thread: Running 3 JCL is much more faster than one JCL with three steps

  1. #1
    Junior Member
    Join Date
    Apr 2007
    Answers
    9

    Running 3 JCL is much more faster than one JCL with three steps

    I´ve got funny problem and no explanation/solution:

    I run a JCL with three steps: sort a file, unload a table, run program. run time is really high (just a few seconds CPU time and more than half an hour).

    If I divide the three steps into three single jcl and submit jcl, every jcl just need a few seconds. So running three jcl is much more faster than one jcl with three steps.

    what can be a reason? Do I have to set some special parameters for scheduling, to get good run time in both cases?


  2. #2
    Contributing Member
    Join Date
    May 2007
    Answers
    85

    Re: Running 3 JCL is much more faster than one JCL with three steps

    Any single JCL job runs its' programs sequentially. If you're familiar with the lower platforms, it's like running a script. No line can run until the previous line has completed.
    Only in this case, no program can run until the previous one has completed.

    When you submit 3 jobs, each gets a different initiator and run simultaneously. In fact, the ability to run many, many jobs simultaneously is the hallmark of a mainframe.
    On a lower platform, this is similar to forking several processes.
    I think if you add up all the time from the 3 separate jobs, you will have slightly higher runtimes and resource usage (wall clock, SRB, EXCP & CPU) than with a single job.

    I'm not sure I understand your question regarding scheduling. If the first step creates a dataset that the second step uses and the second then creates a dataset used in the third, you have no other recourse than to single-thread these jobs.
    If the three steps have nothing to do with one another, then submitting them separately is a good idea.

    In theory, you could use BDT and batch pipes, but based on your question, I’d say you need to gain some more experience before working with those.

    kk


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