I will add on to Sri's excellent answer with my very STRONG recommendation NOT to use hard-coded SORTWK's in your JCL. Both of the major SORT vendors (IBM and Syncsort) do a far, far better job of estimating necessary SORTWK space and memory utilization than any human could hope to do.
I also STRONGLY recommend that you give your JCL and program-controlled SORT steps as much memory in the REGION parameter as your installation allows for production and test jobs. Both of the major SORT programs will figure out how much of that memory to use, whether and how much of it to use in the current WLM environment, and will make VERY effective use of as much of it as they can to cut down on SORT execution and elapsed time. Memory is (relatively) cheap, don't be afraid to use all you've got available to shorten your SORT times. My basic advice is don't try to second-guess these very intelligent programs - they each have more than half a century of practice and experience that none of us can match, even those of us who have been around that long. Peter -----Original Message----- From: IBM Mainframe Discussion List <IBM-MAIN@LISTSERV.UA.EDU> On Behalf Of Sri h Kolusu Sent: Monday, July 3, 2023 12:28 PM To: IBM-MAIN@LISTSERV.UA.EDU Subject: Re: SORTWK space usage >>I will only get the primary space of 5000 cylinders, and the other 14x2000 >>cylinders is never used. Is that right? Billy, No. Incorrect. DFSORT will make use of BOTH primary and secondary space allocations ( 1 primary + 15 Secondary) for a total of 16 extents. So if you allocated 1 sortwk dataset with (CYL,(5000,2000)), then DFSORT would use 5000 + 15* 2000 = 5000 + 30000 = 35,000 cylinders. Also note that the secondary extents will only come into picture ONLY when needed. >>Is there a written explanation I can forward to the programmers so they >>understand this? >>Also (since I know it will come), is there any good way to calculate how much >>DASD sortwork would be used? I know this depends on what is in memory at the >>time, but want to get a better handle on how Sort determines what it needs. I would suggest that you use DFSORT's Dynamic Allocation as it will allocate the required workspace optimally rather than programmers calculating it. The reason is you don't want to change the allocation every time there is an increase/decrease in the number of records to be sorted. Having said that, here is a general formula that you want to use. The amount of sortwk space required depends on the size of the file. It usually ranges from 1.3X to 1.8X of the size of the file to be sorted depending on the sorting path that DFSORT chose. Filesize = Number of records * Avg length of the record ( for Fixed length RECFM=F or FB , it is the LRECL value, or RECFM=V or RECFM=VB is the average length of the record) However, that range is applicable ONLY when the entire file is being sorted using Disk workspace. DFSORT has the capability of using memory (real and auxiliary storage) and if it runs out of it, it will then use disk workspace. Thanks, Kolusu -- This message and any attachments are intended only for the use of the addressee and may contain information that is privileged and confidential. If the reader of the message is not the intended recipient or an authorized representative of the intended recipient, you are hereby notified that any dissemination of this communication is strictly prohibited. If you have received this communication in error, please notify us immediately by e-mail and delete the message and any attachments from your system. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
