ObTRUNCEvery time someone says "I don't believe in theories", another theory dies.
-- Shmuel (Seymour J.) Metz http://mason.gmu.edu/~smetz3 עַם יִשְׂרָאֵל חַי ________________________________________ From: IBM Mainframe Discussion List <IBM-MAIN@LISTSERV.UA.EDU> on behalf of Joel C. Ewing <jce.ebe...@cox.net> Sent: Saturday, November 11, 2023 11:53 PM To: IBM-MAIN@LISTSERV.UA.EDU Subject: Re: Is True Skip-Sequential Processing Possible with RECFM=FB,DSORG=PS? On 11/11/23 21:03, Ed Jaffe wrote: > On 11/11/2023 6:40 PM, Paul Gilmartin wrote: >> On Sun, 12 Nov 2023 02:16:07 +0000, Seymour J Metz wrote: >> >>> Solves what problem? Unix doesn't have records, so you have to >>> impose your own record structure and tell seek the byte offset. >>> >> He said FB. That makes the calc simple. > > FB allows short blocks. FBS would be needed to do true skip-sequential. But of course short blocks, other than the last block, will not be present with RECFM=FB sequential datasets that are created by the usual means with a single OPEN-CLOSE sequence -- internal short blocks only happen when the dataset is created as multiple segments with subsequent OPENs appending to existing records by opening the dataset with DISP=MOD, as each CLOSE has the potential to create a short block. So in those contexts where you know from the way the dataset was created that the "allowed" embedded short blocks cannot actually be present, RECFM=FB works also. If you wanted to verify whether a specific FB-created dataset contained internal short blocks, i believe you could run any utility that would read the entire dataset using JCL to override the dataset RECFM with RECFM=FBS, and you should get some error indication like IEB174I if internal short blocks are found. JC Ewing -- 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
