Scott, Many thanks for addressing this. Not to decry the help from the community here who are frequently a brilliant resource , but I was hoping to a get a reply from someone who had some deeper knowledge of the subject within development. I read the chapter you recommended and realised as I was reading it, that I had read it many years back, when MVS was just MVS and Dynamic Allocation was documented in the Job Management manual. At that time (probably more than 40 years back) I was learning about the text units and so on and I was unclear when to use the permanently allocated attribute and the convertible attribute. Most of the time I wanted to do whatever TSO ALLOCATE would do and I used permanent allocations. The CONCAT command I wrote in the late 80s still works fine with that attribute (available for free here folks, https://rsclweb.com/downloads/#CONCAT-position ).
So that reading has indeed helped and clarified some of my understanding. The problems I am addressing are with allocations at a customer site. They are using zSecure and have trouble allocating large numbers of Access Monitor files. DYNAMNBR does not seem to help. They have a default TIOT size of 64K. Looks like now I have more info to investigate the problems. Maybe I should enquire of the zSecure developers if they use the Convertible attribute and whether they mark allocations as not-in-use. zSecure uses its own code for allocations and it is not always clear what is being done under the covers. Many thanks for the offer of further help. I may take you up on that. Lennie Lennie Dymoke-Bradshaw https://rsclweb.com -----Original Message----- From: IBM Mainframe Discussion List <[email protected]> On Behalf Of Scott Ballentine Sent: 05 December 2024 16:39 To: [email protected] Subject: Re: DYNAMNBR 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 ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
