Re: CHAIN versus SETLL

[rbbaird@xxxxxxxxxxx (Rick Baird)]

boothm@earth.goddard.edu wrote:

> Don't you need to do a setll,
>  then do a read,
>  then do a compare to your key,
>  to see if the record you seek is actually there?
>
> Whereas, with a chain you need only hit the file's index to set on the
>
> no-hit indicator?
>
I think the intent of the questioner was to position the file for future
read(s) (chain with no-hit vs. setll).

IMO, in todays world of big iron, the answer is simple - code it the way
that will make it the most readable.

C    KEY    CHAINFILE            90
 *
C    *IN90  IFEQ *ON
.......etc.

this makes it pretty obvious that the programmer has a complete key, and
wants to know if "a particular" record exists or not.

C    PRTKEY  SETLLFILE
C    PRTKEY  READEFILE                90
 *
C    *IN90   DOWEQ*OFF
C............etc.

This makes it obvious that the intent is to read a set of records, not
just one.

The days of saving a few nano seconds per cycle at the expense of
readability are long over. The instructor should have answered that it
doesn't make any difference which opcode he uses and that the program
should be designed in such a way that you minimize ALL reads/sets/chains
and that if it takes an analyst an extra hour to decifer bad code, this
is much more expensive than the difference between setll/chain

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