Charles, I think that you misunderstood me. I'm suggesting that the cheap first hash (used to rule out common changes) would be over a combination of:
- the first n bytes of the data set (just like you suggested) - the F1/F8 DSCB (which has stuff like DS1LSTAR and DS1TRBAL which helps to detect common changes to the end Kirk Wolf Dovetailed Technologies http://dovetail.com On Thu, Aug 20, 2015 at 12:41 PM, Charles Mills <[email protected]> wrote: > Right. That's a better idea. Seek to end minus 'n' and go from there. > > Only small negative is that if you did the first 'n' bytes and then needed > to do the whole file, you could just keep going rather than starting over. > > Charles > > -----Original Message----- > From: IBM Mainframe Discussion List [mailto:[email protected]] On > Behalf Of Kirk Wolf > Sent: Thursday, August 20, 2015 10:31 AM > To: [email protected] > Subject: Re: Ideas for hash of a sequential data set > > That is certainly a possibility, but wouldn't help in the (common) case of > a change that just appends to the end. Perhaps hashing both the "first n > bytes" with the F1/8 DSCB (which has information about the last TTR and > bytes in the last track) would cover more of the common changes than either > alone. > > ---------------------------------------------------------------------- > 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
