There was an article written by Dan Cruikshank in the 2006:
Modernizing Database Access
The Madness Behind the Methods
http://www-03.ibm.com/systems/resources/systems_i_software_db2_pdf_Performan
ce_DDS_SQL.pdf
... and I'm still convinced he wrote this article because of me. We
discussed in Rochester (where I participated in writing a Redbook) about
database modernization.
First thing to convert the guys in Rochester proposed, was recreating the
physical files with DDL. In my opinion converting the file definition from
DDS to DDL without adding anything new (such as an identity column) didn't
make sense. IMHO there are much more important things to do first, for
examples moving business logic into the database by creating the appropriate
views and/or replacing native I/O with embedded SQL that use the views
mentioned before, adding check constraints ...
I do not convert from DDS to DDL if there are no bigger enhancements, even
though I use the ALTER TABLE statement for changes (and after I always
determine the DDL for the table and store it in a source file).
I'd not convert the DDS described tables before I'll be able to redesign my
database.
Mit freundlichen Grüßen / Best regards
Birgitta Hauser
"Shoot for the moon, even if you miss, you'll land among the stars." (Les
Brown)
"If you think education is expensive, try ignorance." (Derek Bok)
"What is worse than training your staff and losing them? Not training them
and keeping them!"
-----Ursprüngliche Nachricht-----
Von: MIDRANGE-L [mailto:midrange-l-bounces@xxxxxxxxxxxx] Im Auftrag von
Scott Klement
Gesendet: Sunday, 26.10 2014 02:10
An: Midrange Systems Technical Discussion
Betreff: Re: Can I use DDS to create an SQL table name
My problem with the whole "do it because there's improved performance"
angle is this:
DDS didn't hurt me, performance-wise, back in 1989 when I first started on
the AS/400. I never noticed any performance difference between the
S/36 (program-defined) disk access and the new (at the time) external
definitions.
But now I'm being told to switch to DDL to perform better over DDS, despite
that my computer is 1000 times faster, etc, etc. It just doesn't make a lot
of sense.
I do create new tables with DDL, and if I'm doing a major overhaul on an
older table, I take the time to update it to DDL. But, not for
performance... for the other reasons.
The performance angle just doesn't make much sense.
On 10/25/2014 3:49 PM, Jon Paris wrote:
Agreed that validation on write is great - no argument.
But there is no validation on read and that?s where I disagree with Dan
claiming a performance boost. At least as far as RPG native IO is concerned,
for SQL access maybe that is the case.
For native I/O bad data will either cause an explosion or (in the case of
DS I/O) potentially be ignored. So it really doesn?t matter if reads
outnumber writes 25 to 1 because if it blows up once you probably go an fix
it! You don?t leave it to blow up again and again.
I find a lot of the DDL performance advantages being touted are not really
valid in a real world scenario. Not to say there aren?t other good reasons
to use DDL - particularly for new tables - but the cost of switching and the
benefits gained are a much finer balance.
Jon Paris
www.partner400.com
www.SystemiDeveloper.com
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