RE: Buffering and single level store (was RE: chain problem)

[CWilt@xxxxxxxxxxxx]

> -----Original Message-----
> From: Dan Bale [mailto:dbale@xxxxxxxxxxxxx]
> Sent: Friday, August 13, 2004 4:02 PM
> To: RPG programming on the AS400 / iSeries
> Subject: RE: Buffering and single level store (was RE: chain problem)
> 
> 
> <Valley girl tone> W-h-a-t-e-v-e-r...  <g>
> 
> Seriously, though, it seems that this should be easy stuff for an
> object-oriented, SLS system.  The OS has to know that there 
> are records in
> memory that are more current than what's on the disk.  How 
> hard can it be?
> (asks the RPG programmer).
> 

Dan,

I think the answers is, with blocking the OS doesn't know <grin>.  From the
link Eric gave, (apologies if you read it in my post to him ;-)

The system reads a block of records into the system buffer (located in the
Open Data Path (ODP) for that file) when the first read in the user's
program is run and then moves the first of these records into the program
buffer so the program can process that data. When the program next performs
a read, the next record in the block is moved into the program buffer by the
program (no system calls are made). <snip> Writes are essentially the same.


Notice that "(no system calls are made)".  The system doesn't have any clue
what's been done with the block of bytes it loaded.

The gist of the info I got from the link Eric gave was this: blocking is
used for performance in batch processes.  For interactive or simultanious
access, blocking should be off (or at least tightly controlled ;-)

With blocking off, the object-oriented SLS system is allowed to work as we'd
expect.

Charles