• Subject: Re: Early Client Server on the AS/400
  • From: nina jones <ddi@xxxxxxxxxxxxxxxxx>
  • Date: Fri, 01 Jan 1999 09:47:05 -0600
  • Organization: data design inc http://www.datadesigninc.com

> >downsides are pure communication speed.  if your files are large, and you 
>are only
> >using a little bit of data, the entire file has to be transmitted.  in some 
> >this won't work well.
> This isn't quite true.  Most of the overhead in DDM is purely due to 
>communications line speed.  There
> is some additional overhead when using DDM between AS/400 or S/38 and the DDM 
>extensions for those
> platforms are used resulting in extra data being transmitted.  The trade-off 
>is reduced processing at
> the source because a more intelligent request can be made of the target 
>system but it can result in
> bandwidth limits being reached sooner than expected.

> The only instance where an application may suffer additional degradation is 
>when duplicate-key files are
> being processed with READE operations.  In this case the source system 
>performs a READ-NEXT and compares
> the key value (much like RPG performs with partial-key operations) resulting 
>in the likelyhood of
> unnecessary records being returned to the source and discarded.
> OPNQRYF can be used to remedy the above situation in most cases because the 
>query is sent to the target
> system (using the S/38 and AS/400 DDM extensions) and the target returns only 
>the result set -- much
> like SQL and DRDA.  Blocking can also be used for sequential access to 
>improve throughput.

excuse me, i should have said 'downsides are pure communication line speed'.

in the early 90's we had an application that needed to be networked between 
as/400.  there was a lot of
contstruction on the fly of the data, and the result was 2 minute response time 
over 9600 lines using ddm.

so we used icf instead.  but remember this was 6 years ago, and i wouldn't do 
it that way today.

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