RE: Logical file order of records

On Thu, 2009-11-05 at 21:21 +0000, Neill Harper wrote:

...
The subtle difference was finally tracked down to the order that the logical
files were returning records.
...
Both files were compiled from the same dds using the same commands params,
they don't reuse deleted records

And, I take it, the DDS did not specify the order for records with equal
keys. So both results were correct.

My knowledge of this area is old, and it may have been overtaken by
subsequent changes. But what I remember is this ...

When the system creates a LF, it will share any already-existing index
which serves the purpose. When you allow duplicate keys without
specifying duplicate key ordering, you can end up with FIFO, LIFO, or
the sequence of some other field of the record.

Just to confuse the issue a bit, restoring a LF or duplicating one, is
equivalent to creating it for the purposes here.

The short answer still applies: specify the sequence you need.

Cheers,
Terry.

-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx
[mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of Crispin Bates
Sent: 05 November 2009 20:37
To: Midrange Systems Technical Discussion
Subject: Re: Logical file order of records

Neil,

It depends. What do you mean by identical data?

There was an interesting discussion on the System i network last week
regarding this.

http://forums.systeminetwork.com/isnetforums/showthread.php?t=77551

It is possible that two versions of the same physical, with the same data,
can return the data in different sequences. It really depends on what you
mean by identical data. The data may have been written in a different
sequence, one physical may have been RGZPFM'd. If REUSEDLT(*YES), then what
sequence does the system decide to write to deleted records in?

Don't write applications that rely on data to be sequenced without defining
that sequence as keys. SQL will never guarantee the sequence except for what

is in the ORDER BY. Use the same approach for DDS LF's and you won't get
bitten. If you want to see records in the order they are created, the you
need a Date/Time stamp to sequence them by...

Crispin.

----- Original Message -----
From: "Neill Harper" <neill.harper@xxxxxxxx>
To: "'Midrange Systems Technical Discussion'" <midrange-l@xxxxxxxxxxxx>
Sent: Thursday, November 05, 2009 3:02 PM
Subject: Logical file order of records

If I have a unkeyed PF FILEA as follows:



Field1, Field2, Field3, Field4



I then have an LF LFA, with a non unique key of Field1,Field2,Field3



When there is more and one record with identical Field1,Field2 and Field3
columns, what controls the order of the remaining records.



Further to this, if I had 2 copies of FILEA in different libraries with
EXACTLY the same data in would you expect LFA in both libraries to show
the
records in exactly the same order?









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