RE: Journaling for data recovery - Lost records.

I am not clear of the technical details but I am 99% (I would say 100% but
then I've been wrong on some occasions in the past) sure that at IPL either
with both records or neither record will exist.  An IBM database recovery
guru could supply how that happens.

Don
Tully Consulting LLC

-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx
[mailto:midrange-l-bounces@xxxxxxxxxxxx]On Behalf Of Walden H. Leverich
Sent: Sunday, January 16, 2005 1:39 PM
To: Midrange Systems Technical Discussion
Subject: RE: Journaling for data recovery - Lost records.


>RI always requires that parent row be written prior to child row.
>If attempt to write the child first is processed, that will be
>immediately followed with a rollback transaction.

True. But the parent row was written before the child, it's just that
the child had been pushed to disk but the parent hadn't when they lost
power. So the inserts would have been ok, but since we lost data we'd
not have a child w/o a parent.

>I would not want to run without journaling or RI.

No argument from me there.

-Walden

------------
Walden H Leverich III
President & CEO
Tech Software
(516) 627-3800 x11
WaldenL@xxxxxxxxxxxxxxx
http://www.TechSoftInc.com

Quiquid latine dictum sit altum viditur.
(Whatever is said in Latin seems profound.)


-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx
[mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of Don Tully
Sent: Sunday, January 16, 2005 1:38 PM
To: Midrange Systems Technical Discussion
Subject: RE: Journaling for data recovery - Lost records.

All machines (and customers) of mine have used journaling since 1992.
All systems that I have built since 1995 have used RI on all non-work
files.  RI always requires that parent row be written prior to child
row.  If attempt to write the child first is processed, that will be
immediately followed with a rollback transaction.

Journaling can be very "expensive" if the application is poorly written.
By that, I mean retrieving of records for update-- requiring record
locking-- and updating with the same image or only change is to audit
time stamp.  The old update primary file program where only a very small
portion of the records actually needing to be updated. If those culprit
programs are corrected, journaling has a minimal impact.. maybe in 3 to
5% range.  At least that has been my experience.

Journaling also provides a gold mine for testing.  Rather than just
looking at some end results, examine the journal and see all of the
database updates.  One is often amazed at updates that would otherwise
surely go unnoticed until down the road and  some seemingly unrelated
data problem is noticed.

I would not want to run without journaling or RI.

Don Tully
Tully Consulting LLC

-----Original Message-----
Subject: Journaling for data recovery - Lost records.

...
On a related topic, what would have happened if we had declared RI
between the invoice detail and invoice detail-detail tables? Would we
now have a child row w/o a parent row?

I told the client that he should turn on journaling on all his files as
standard practice, but I got the old "Journaling is too expensive"
response. I know that has changed over the years, but does IBM have any
whitepapers to that effect?

-Walden

------------
Walden H Leverich III
President & CEO
Tech Software
(516) 627-3800 x11
WaldenL@xxxxxxxxxxxxxxx <mailto:WaldenL@xxxxxxxxxxxxxxx>
http://www.TechSoftInc.com <http://www.techsoftinc.com/>

Quiquid latine dictum sit altum viditur.
(Whatever is said in Latin seems profound.)


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