RE: "extract" command enhancement (subfiles and BIFs)

How did your program skip 64 records at a time, using a keyed file?  I was
under the impression that you can't use RRN to advance the records on keyed
files (already sorted) ...Or do you have an ODP that's already sorted, and
use the RRN on that file but just do put the 'K' attribute on the F spec?
tim

        -----Original Message-----
        From:   David Morris [SMTP:dmorris@plumcreek.com]
        Sent:   Thursday, September 23, 1999 3:07 PM
        To:     RPG400-L@midrange.com
        Subject:        Re: "extract" command enhancement (subfiles and
BIFs)

        Jim,

        I recently spent some time trying to optimize a page by page subfile
positioning 
        routine.  I started by reading every 4096th record until I hit a
greater key and then 
        went back/forth by half until I hit 1 or the key.  Worked pretty
good, but it was slower 
        than my sequential search which just read every 64th record and then
backed up 
        when it found a key greater.  I found out that with a scrollable
cursor, to get the 
        record n records away the system actually performed I/O for all of
the inner 
        records.  Seems odd to that the system performs I/O when simply
counting index 
        entries would do. 

        David Morris

        >>> Jim Langston <jlangston@conexfreight.com> 09/23/99 01:24PM >>>
        Incidentally, this "halving" technique is one I learned years ago in
school from a
        math teacher.  By using the halving technique, you can pick any
number from 1
        to 100 within 7 "guesses", with the average being 4 or 5 (not 3.5
because of the
        refinement on each consecutive pick)..  On a simple sequential
search, 1, 2, 3,
        4, etc... it could take 100 picks, with the average being 50.  With
1000 records
        the halving technique would take at most 10 guess, and I'm not even
going to
        try to figure out the average (7 maybe?).  With sequential search,
max 1000 and
        average of 500.

        It's a really good technique, and I have used it in searches before,
but there is
        the necessity that your data is sorted on what you're looking for.
And this is
        basically the exact same way the OS does it when it does a SETLL.

        Regards,

        Jim Langston


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