Take a look at the Control Limit information in the dynamic allocation description in the MVS Authorized Assembler Services Guide: https://www.ibm.com/docs/en/zos/2.4.0?topic=functions-control-limit . (It's probably worth taking a look at the In-Use Attribute information too, it's the topic immediately before that Control Limit topic.) Basically, it's our cap on the number of things that are marked not-in-use before we start unallocating those not-in-use DDs.
I can't really explain why DYNAMNBR and the control limit are a useful feature in dynamic allocation. It's kind of a backwards limit in that it doesn't really prevent you from allocating too many DDs. It does prevent you from allocating DDs if you've removed the in-use attribute from too many DDs and for some reason we can't unallocate those DDs automatically. It's not directly tied to TIOT size (although TIOT size factors into how large you can set the value to be), and it doesn't directly limit how many dynamic allocations you can do. I wouldn't quite go as far as saying "compliance with it is voluntary", and it is managed within SVC 99 itself (so technically it applies to functions like TSO ALLOCATE and BPXWDYN that invoke SVC 99.) It also is not directly tied to the DVC in the SMS DATACLASS - that value has implications for how large the TIOT entries are (among other things). With all of that... in my experience, rarely do you need to deal with setting DYNAMNBR. If you're removing the in-use attribute from DDs, you might need to worry about it, but I'm not sure how common that is these days. That's a lot of information... how useful it is, I'm not sure, and if you've got more questions I'll try to answer as best I can. -Scott Ballentine IBM z/OS Device Allocation [email protected] ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
