RE: Early Client Server on the AS/400 -- MIDRANGE-L

>>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 
>cases,
>>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.

My understanding is somewhat different here. I started off by providing DDM 
access to a Salesman file for
system A when the file actually resided on system B. It worked great. It was 
used to provide a name to
go along with a Salesman Number on an inquiry screen. Then pretty soon they 
wanted to use it to
validate Salesman numbers for an entry screen. Again, it worked like a champ. 
Then they wanted a
lookup window to pick the Salesman from. Here is where the performance went to 
hell! DDM is built
for record at a time access and not multiple records. I switched to APPC 
communicvations and the
performance improved 700% - 800% (this is not a typo). With APPC, the overhead 
is incurred once when
the communication programs are started. With DDM, the overhead is incurred on 
every record. As long
as you are doing a single record, DDM provides an easy way to accomplish your 
task. As soon as you
start to access more than a single record, you really start to pay a price. 
APPC programming is more
complicated than DDM, but not impossible to learn. I learned how to do it at 
COMMON. Alan Olson
gave me everything I needed in a 2hr session to go back to my job and implement 
APPC in my programs.
This all happened several years ago, but I don't think DDM has changed that 
drastically. APPC offers
several other advantages including sending multiple records in a single 
transfer, sending a subset of
fields (only the ones you want) and mixing records from multiple files (order 
header, corresponding
order detail, order comments, etc). SQL stored procedures is very similar as I 
understand them.

Joe Teff
application/ms-tnef