FRCDTA vs DFRWRT(*NO)

[John Carr <74711.77@xxxxxxxxxxxxxx>]

WAS -  RE: ERRMSG Keyword in display files....

>Very interesting.  Could you elaborate?  What makes DFRWRT(*NO) so   
>undesireable?
> --
>Brian Johnson
>Help/Systems, Inc.
>brian@helpsystems.com
>----------
>>From:  John Carr
>>Sent:  Sat, Jun 28, 1997 14:22 PM
>>Subject:  RE: ERRMSG Keyword in display files....
>>...
>>except only for the one format.  DFRWRT(*NO) for the whole display file
>>is NEVER A VERY DESIRABLE to do.  (ya see, you guys I am concerned about
>>...  

Brian

I believe that if you have a display file which is DFRWRT(*NO) then
whenever you do a WRITE to a format (maybe something like;  
WRITE  HEADING
WRITE  CMDS
WRITE  MSGSFL
EXFMT  SFLCNTRL

OS/400 will do each I/O IMMEDIATELY when the WRITE is encountered. 
Your program goes into a WAIT STATE (while still in an activity slot)
each time this happens. VERY EXPENSIVE. (Especially remotely attached)

Its like taking the groceries out of the car into the 
house by carrying each item seperately one at a time.  

If you do the same thing with the display file DFRWRT(*YES),
OS/400 will "bundle up or buffer up" all the writes UNTIL it sees 
an Input/Output operation like a READ or EXFMT.  When it encounters 
that opcode it writes the whole "bundle or buffer"

Using my analogy, it makes one trip to the house with all the groceries
in the bag.

By using FRCDTA only on one format, you get the effect you want for that
one format, and not have to pay the price for EVERY format. 
You can even use conditioning indicators with this FORMAT level keyword.

To quote the DDS manual;  "With DFRWRT(*YES) specified, none of the record
formats is displayed until the input operation." (ie EXFMT or READ)

John Carr CDP
EdgeTech 


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