Re: Access Key for a Sub File ?

[email@xxxxxxxxxxxxxxxxxxx (James W Kilgore)]

Sounds like a natural for RRN halving.

If you've not done this before, here's a quick review:
1) As you load the subfile, save low voucher value.
2) As you load the subfile, save high voucher value and last RRN
written.
3) When receiving a "position to" request, validate that it is within
low/high range.
4) Initialize working low/high RRN. (low=1, high=last written)
5) CHAIN subfile record at ((highRRN-lowRRN)+1)/2
6a) If retrieved voucher value is less than requested voucher, set
lowRRN to current RRN.  (You want the second half of the file)
6b) Else set highRRN to current RRN (You want the first half of the
file)
6c) Go to step 5

We get out of this loop when retrieved value matches requested value or
when the highRRN-lowRRN is <= page size. In the latter case we start a
record by record loop/compare as originally suggested.

If the user will be doing a lot of positioning, you may want to get the
25/50/75% values right after loading the subfile and eliminate 2 CHAIN
operations with each positioning by doing a simple compare instead and
then set lowRRN and highRRN accordingly.

As you see, half of the file is eliminated with the first CHAIN, half of
the remaining half is eliminated with the second CHAIN.  Each CHAIN
eliminates half of the remaining file record range.

Give it a try, I think you'll be pleased with the response time.

James W. Kilgore
email@James-W-Kilgore.com

P.S. BTW this can also be used to speed up LOKUP operations on an
ordered array.




Adhip C Lahiri wrote:
> 
> Folks,
>         I have a fairly complicated code that amongst other things
> has  a one-shot build subfile which also has a subfile field called Voucher.
> I need to implement a new "position to"  using a  Starting Voucher search
> field in the control.
+---
| This is the Midrange System Mailing List!
| To submit a new message, send your mail to MIDRANGE-L@midrange.com.
| To subscribe to this list send email to MIDRANGE-L-SUB@midrange.com.
| To unsubscribe from this list send email to MIDRANGE-L-UNSUB@midrange.com.
| Questions should be directed to the list owner/operator: david@midrange.com
+---