What you described about VSAM is what I heard too, a replacement of the then dominant access methods.
Sent from Proton Mail Android -------- Original Message -------- On 5/24/24 8:18 PM, Joel C. Ewing <[email protected]> wrote: > 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 [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
