One of the things that made KSDS viable was the CI, which let existing programs continue to run after moving off of ISAM; I considered it to be a blunder that MVS failed to do so for ESDS. I was also unhappy that VSAM did not include the functionality of VAM in TSS, especially VIPAM.
-- Shmuel (Seymour J.) Metz http://mason.gmu.edu/~smetz3 עַם יִשְׂרָאֵל חַי נֵ֣צַח יִשְׂרָאֵ֔ל לֹ֥א יְשַׁקֵּ֖ר ________________________________________ From: IBM Mainframe Discussion List <IBM-MAIN@LISTSERV.UA.EDU> on behalf of Joel C. Ewing <jce.ebe...@cox.net> Sent: Friday, May 24, 2024 8:18 PM To: IBM-MAIN@LISTSERV.UA.EDU Subject: Re: VTOCs vs. catalogs VSAM KSDS datasets were a clear win as a replacement for Indexed Sequental (ISAM) datasets when adding large numbers of keyed records. I saw cases where a KSDS implementation literally ran two orders of magnitude faster than ISAM and also took less DASD space, because ISAM required that unblocked overflow records be serially searched when there was no remaining space in a block to insert a record with a given key. In theory an ESDS dataset could be used to replace a sequential dataset and BSAM/QSAM, but of course the application interfaces were considerably different, and VSAM constraints on block size meant you could take substantial hits on track efficiency and performance for certain logical record sizes. An RRDS could be used as a functional replacement for direct access files, but again the restriction on block sizes caused compatibility issues, and tuning RRDS dataset access to get performance comparable to a well-tuned BDAM application was difficult to impossible. You could probably have designed a functional replacement for PDS datasets with either a KSDS or RRDS organization, or a combination of KSDS and ESDS, but it wouldn't have been practical. Many decades later PDSEs are almost a tranparent replacement for a PDS, but there are still some things possible with a PDS that are not supported for a PDSE. If VSAM's goal was to replace all other file organizations, it failed. The only old dataset organization to be made totally obsolete by VSAM was ISAM. JC Ewing On 5/24/24 10:02, Paul Gilmartin wrote: > On Thu, 23 May 2024 22:24:06 -0500, Mike Schwab wrote: >> VSAM came from the Future Systems development as a complete >> replacement, Lynn Wheeler has posts about that. >> It was cut back to be an addition to MVS, then combined with CVOL >> catalogs to ICF. >> > "complete replacement" of what, specifically? I have heard the > assertion that VSAM was intended to replace all other access > methods: QSAM, BSAM, BPAM, ... > > ... -- Joel C. Ewing ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
