Re: Why do people set up their batch submission defaults to run multiple batch jobs at the same time?

On Thu, May 6, 2010 at 22:46, James H. H. Lampert
<jamesl@xxxxxxxxxxxxxxxxx> wrote:

For probably the fourth or fifth time, I had to clean up a mess that was
partly caused by two batch jobs (running the same program!) getting into
exactly that sort of fight, for exactly that reason.

Isn't "running jobs sequentially, one at a time" the essence of batch
processing?

No. Proper program logic should ensure that something like this can't
be destructive - running the same job twice should result in a "job x
is already running" message. This can be achieved by proper locking.
Forcing a single-batch job to fix problems in the application logic..
Well, it works - but it's a workaround, not a proper solution.

What can be a reason for running only a single batch job can be
performance, but this is going to be less and less of an issue.

Machines nowadays have multiple cores and many, fast disk arms (or no
disk arms and NAND instead). Most IBM i programs are single-threaded,
and thus it makes sense to have several CPU bound jobs running in
parallel, to use up all the cores you have. If you're doing something
IO intensive, it depends. Disk contention on a four-disk, mirrored
machine is fairly easy to get, and running only one job at a time may
improve performance. If you have a larger system, it won't matter as
much and you'll be done sooner running multiple jobs in parallel.