DDM vs ICF Was: Early Client Server on the AS/400

-snip some good bits about DDM vs ICF-

DDM can indeed be a poor performer if you make typical DDM
decisions, i.e. make no changes to the application aside
from overriding to a DDM file.

DDM *does* have more overhead if only because people who write 
ICF programs rarely include much in the way of handshaking or 
error handling.  DDM does the handshaking and error handling
"under the covers".  Clearly, if you send less stuff back and 
forth across the comm line, your total time to run will be lower.

Also, the ICF folks tend to think about the data stream: if you 
need a name, then they send back only a 30 byte name.  The DDM
folks usually CHAIN and bring back the whole 210 byte record.
With a minor change, they could build a LF on the target system
that only contains the name.  CHAIN still returns the whole record,
but the record it returns is much smaller: just the name.

If you want to do some serious comparisons, run some line
traces and watch the stuff that moves across the line.  It's an 
eye opener.  Like Simon says (!) many performance problems are
masked by the relatively high speed of a LAN or even a Twinax
connection.  Anything that saves I/O will provide you with 
several advantages: 1) you can run more users on the same box,
2) you can speed response time and 3) you can add more applications
to the box without requiring an upgrade. 

Buck Calabro
CommSoft, Albany, NY
mailto:mcalabro@commsoft.net


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