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  2. RPG400-L
  3. December 2005

Re: Date Field block size


On 24/12/2005, at 8:23 AM, Tony Carolla wrote:
I have seen the NBRRCDS() parm, and I have tried to use it, but for some reason, it doesn't seem to make the READs read more records in the buffer. 
I am usually trying to read from a file in key sequence (which makes
SEQONLY() _sound_ like the wrong parm to use). If I use SEQONLY, I can view 
the number of records read as the job is running, and see that it is
grabbing more records at a time.  If I use NBRRCDS, it only grabs the
default number of records.
NBRRCDS controls the number of records read into main storage. Think of this as physical I/O. A read from DASD occurred.
SEQONLY controls the number of records read into the program buffer. Think of this as logical I/O. A read from main storage occurred.
Thus NBRRCDS can be used effectively with random I/O and with update files by caching records into main storage (much like SETOBJACC) but SEQONLY can only be used with sequential I/O but that includes sequential-by-key too. 

Specifying both NBRRCDS and SEQONLY is known as double-buffering.
The I/O count in Display Open Files is only the logical (or program) I/O count. It doesn't show I/O that brought records into main storage. This makes sense because a program could read records brought into main storage by a different job. 

Regards,
Simon Coulter.
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