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

Charles,

I found some decent info on IBM's site:
http://www-1.ibm.com/support/docview.wss?uid=nas1d6738e1cd37e1f33862565c2007
cef79&rs=110

Regarding buffering and SLS, my understanding of this is that SLS is just a
big memory map that encompases all storage within the box.  The fact that a
database file is associated with a particular memory address does not impart
any real performance benefit.... It just makes the management of those
resources simpler.  When you access a file that is stored on DASD, the OS
must still copy that data from the device into main storage.  From main
storage, then, it gets sent to the application in discreet chunks.  Record
blocking sends larger chunks, saving on overhead.


Eric DeLong
Sally Beauty Company
MIS-Project Manager (BSG)
940-898-7863 or ext. 1863



-----Original Message-----
From: CWilt@xxxxxxxxxxxx [mailto:CWilt@xxxxxxxxxxxx]
Sent: Friday, August 13, 2004 12:08 PM
To: rpg400-l@xxxxxxxxxxxx
Subject: RE: Buffering and single level store (was RE: chain problem)


Eric,

After reading your other post and giving it some more thought.  I'd have to
say that the blocking is being done by  "above" the OS and the single level
store.

But that leads to the question: with all the technology (caching) in the OS
and in the hardware, shouldn't we be able to turn off the RPG blocking
without detrimental impact?

Seems like the answer should be yes, but if I recall correctly recent posts
have mentioned that blocking still provides an improvement.  I wonder why
this is so.  Maybe just less overhead since there's less calls to the OS?


Charles
  



> -----Original Message-----
> From: DeLong, Eric [mailto:EDeLong@xxxxxxxxxxxxxxx]
> Sent: Friday, August 13, 2004 11:18 AM
> To: 'RPG programming on the AS400 / iSeries'
> Subject: RE: Buffering and single level store (was RE: chain problem)
> 
> 
> Charles,
> 
> I don't think single level store has much to do with IO 
> blocking....  Data
> management handles the retrieval of data, and can decide to 
> block the data
> as it deems necessary (or as we explicitly tell it).  Our RPG programs
> simply ask OS400 for data.  If blocking is enabled, then data 
> management
> simply retrieves multiple records in succession and loads 
> that data into the
> buffer.  Subsequent sequential reads or writes are simply 
> applied against
> the copies of data in the buffers, and may or may not 
> actually fetch or
> write to DASD.  
> 
> Eric DeLong
> Sally Beauty Company
> MIS-Project Manager (BSG)
> 940-898-7863 or ext. 1863
> 
> 
> 
> -----Original Message-----
> From: CWilt@xxxxxxxxxxxx [mailto:CWilt@xxxxxxxxxxxx]
> Sent: Friday, August 13, 2004 9:53 AM
> To: rpg400-l@xxxxxxxxxxxx
> Subject: Buffering and single level store (was RE: chain problem)
> 
> 
> I read the same article.
> 
> One of the discussion posts about the article asks an 
> interesting question,
> "What happened to single-level store?"
> 
> >From my, admittingly simple, understanding of single level store the
> buffering problem should really exist.  Yet obviously it 
> does.  Does anyone
> know why?
> 
> Thanks,
> Charles
> 
> 
> > -----Original Message-----
> > From: Haas, Matt [mailto:Matt.Haas@xxxxxxxxxxx]
> > Sent: Friday, August 13, 2004 9:36 AM
> > To: RPG programming on the AS400 / iSeries
> > Subject: RE: chain problem
> > 
> > 
> > A newsletter I get from MC Press had an article on this 
> > subject today. The link I have for the article is 
> > http://www.mcpressonline.com/mc/1@xxxxxxxxxxxxxxxx@.6aecd92d. 
> > You'll need to register for the site to access it.
> > 
> > Matt
> > 
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