> Who said SVS did not have VSAM? Steve Thompson
> SVS certainly did have VSAM Indeed. -- Shmuel (Seymour J.) Metz http://mason.gmu.edu/~smetz3 ________________________________________ From: IBM Mainframe Discussion List <[email protected]> on behalf of Mark Waterbury <[email protected]> Sent: Wednesday, September 5, 2018 6:19 PM To: [email protected] Subject: Re: VSAM share-option 4 Who said SVS did not have VSAM? SVS certainly did have VSAM ... It was an ICR -- Independent Component Release -- so somewhat tricky to get it installed into SVS, but once installed, it did work... and CICS/VS used it ... This was on SVS 1.7 circa 1976-77... And, just like on MVS, on SVS, we were taught that: Share options means 3 Close your eyes 4 Close your eyes and step on the gas! Does that jog anyone's memory? Mark S. Waterbury On Wednesday, September 5, 2018, 12:35:26 AM EDT, Seymour J Metz <[email protected]> wrote: > VSAM was implemented at the OS level with DOS/VS (and IIRC, > DOS/VS was first to have VSAM with MVS|VS1 to follow), where with > OS (OS/VS1 or MVS) What was SVS, chopped liver? -- Shmuel (Seymour J.) Metz http://mason.gmu.edu/~smetz3 ________________________________________ From: IBM Mainframe Discussion List <[email protected]> on behalf of Steve Thompson <[email protected]> Sent: Tuesday, September 4, 2018 8:35 PM To: [email protected] Subject: Re: VSAM share-option 4 Yes your reading and interpretation is essentially correct. VSAM was implemented at the OS level with DOS/VS (and IIRC, DOS/VS was first to have VSAM with MVS|VS1 to follow), where with OS (OS/VS1 or MVS) it was implemented at the address space level. Whoever did your migration, if they did not have a background involving DOS/VS_ and just did a flat migration to MVS (z/OS), you can get royally shafted. The SHARE OPTIONS between the two systems are very different and one has to know and understand this to do a proper migration and Catalog structures are very different between the two systems. Where you would do backups by CATALOG, a CATALOG does not OWN the volumes in an MVS shop. But they did in a DOS/VS shop. And I hate to break this to you at this late date, but if the migrators didn't know it, the z/VSE system was an XA I/O system and so the performance increase for I/O that one expected in days of yore in going to z/OS will not be there (until DOS/VSE/ESA, DOS systems were BASE S/370 using the OLD SIO/SIOF, etc. and not SSCH and related instructions). You may actually lose performance in the z/OS environment as a result. Regards, Steve Thompson On 09/04/2018 07:42 PM, Tony Thigpen wrote: > My main background is z/VSE but now I have to manage a bunch of > z/OS sites, including one that recently converted from z/VSE to > z/OS. > > On z/VSE, share-option 4 means that VSAM will prevent any read or > write integrity exposures when multiple tasks are accessing the > same VSAM file. > > z/VSE VSAM will internally lock any CI that is being updated so > that nobody else can update the CI. This ENQ/DEQ is handled by > the IBM provided VSAM IO routines at the task level. > Additionally, VSAM will flush all update buffers after a write or > update. And, it will not buffer reads when reading a share-option > 4 file. (I am being somewhat general in the descriptions, so the > details are a little more complicated.) All this to make sure > that the records on disk and the records in buffers match. > > Now, with z/OS, my reading of the VSAM Demystified RedBook leads > me to the following: > 1) Share-option 4 allows multiple open for update, but expects > the program, not the VSAM subsystem, to perform the ENQ/DEQs. > 2) If a program does not perform ENQ/DEQs, then data integrity is > lost as multiple tasks can update the same record concurrently. > 3) VSAM/RLS is one way to protect the data, but that is another > can of worms. > > Am I understanding the z/OS side correctly? > ---------------------------------------------------------------------- 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 ---------------------------------------------------------------------- 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
