why DYNAMBR=20 only ?

vab987 · New User Joined: 01 Dec 2006 Posts: 29 Location: S.A

Hi all,

As per IBM definition :- DYNAMNBR tells the system to hold a number of resources in anticipation of reuse.

What are the resources that System holds for reuse ?
Another question is I have always seen DYNAMBR=20, why is it so ?

Regards,
Vaibhav

jeevan_pattanaik · New User Joined: 02 Nov 2005 Posts: 5 Location: Pune,India

You normally specify all the data sets you need with the DD statements in your JCL for a step, if you write programs that dynamically allocate data sets, you should code the DYNAMNBR parameter on the EXEC statement so the system can acquire the resources just before their use and release themm immediately after use.
You code //stepname EXEC DYNAMNBR=n
The n tells the system how many data set allocations to hold in aniticipation of reuse.( The system actually holds n plus the total number of the DD statements used by the step.

Anuj Dhawan · Posted: Mon Sep 07, 2009 8:26 pm

Just other thread: ibmmainframes.com/post-44303.html

vab987 · New User Joined: 01 Dec 2006 Posts: 29 Location: S.A

Thanks, but I am still stuck why every where DYNAMNBR is set to 20 only, nothing else ?

Robert Sample · Posted: Tue Sep 08, 2009 3:04 pm

Inertia -- probably one of IBM's sample programs used DYNAMNBR=20 and so everybody started using it, not realizing the significance of the value. My batch TSO sessions use 200 not 20, but then I do some things applications programmers don't generally do.

Anuj Dhawan · Posted: Tue Sep 08, 2009 3:53 pm

Just to have some satisfaction, using ISPF 3.14, search on "DYNAMNBR=" in your base line PROC library. Check if you've some other values used for DYNAMNBR. At my shop, most procedures are using value as 20 but there are many other which use 40, 35, 25 and so on...

vab987 · New User Joined: 01 Dec 2006 Posts: 29 Location: S.A

Thanks, even at my shop it is 20.

Thanks all!
Vaibhav

Anuj Dhawan · Posted: Wed Sep 09, 2009 2:45 pm

You're welcome. Hopefully, replies provide you a direction (at least).

Have a good one,

MBabu · Posted: Wed Sep 09, 2009 11:57 pm

This is a really funny question so I searched the IBM website for DYNAMNBR=20 and there are a zillion hits in examples so that is probably where it comes from. As has been said, nothing special about 20. Most systems I worked on seemed to always use 99 for no good reason. The books only have a few DYNAMNBR=99 hits.

vab987 · New User Joined: 01 Dec 2006 Posts: 29 Location: S.A

Thanks everyone for you help !!