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

In client/server these considerations become important but I am surprised at 
the speed and responses I get without doing anything other than using the code 
as offered.  On the LAN the responses seem lightning fast and even over a 28.8 
modem the response times are certainly acceptable.  I have no way of knowing, 
but I am guessing that IBM has tailored something for VaRPG in order to give 
fast responses.  

For example on an application with three subfiles over the same 50,000 record 
physical file,  using page at a time, when the user clicks on the column 
heading to show the file in another sorted order, the new page is filled in 
almost immediately, certainly within 3 seconds on the LAN and within 8 seconds 
over the modem.


In <60F780A9323BFA45052566EF005A7DE9.0000000000000000@commsoft.net>, on 
01/04/99 
   at 11:58 AM, Buck Calabro/commsoft<mcalabro@commsoft.net> said:


>-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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Booth Martin
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