Re: To Key or Not To Key a Physical

Walden has pretty much answered this, but let me reiterate.

Remember, the i is object-based.

With a keyed physical, the *FILE object has (conceptually) two parts,
a data part and an index/access path.

An additional logical file contains just an index/access path part
over the data part of the physical. It doesn't care that the physical
*FILE object also has an access path part.

As for why primary keys are standard, that's pretty much a result of
SQL and relational DB theory. Having a primary key makes life easier
if you are interfacing externally. Also, for example CPYF
MBROPT(*UPDADD) won't work without a unique keyed physical.

Way back when, it was recommended not to have key physicals due to
recovery concerns, but that hasn't been applicable in a long time.

Charles

On Thu, Mar 26, 2009 at 2:41 PM, Kurt Anderson
<kurt.anderson@xxxxxxxxxxxxxx> wrote:

I tried looking online for more information about how indexing occurs and couldn't pinpoint it.

Maybe an example will help.
I want two keys over a file:
Key1: FieldA, FieldB
Key2: FieldB, FieldA

Option 1 is to have an arrival sequence Physical and 2 Logicals.
Option 2 is to key the Physical (let's say Key1) and then make a Logical, Key2.

I've always preferred Option 2 for the simple reason of: hey, 2 files instead of 3; however I've been approached with the thought that Option2 will index over an index which would be less preferable to indexing over a non-keyed Physical.  Is this a valid concern?

Charles, you say that it's the general standard to always key the Physical.  I guess I'm looking for the reasoning behind that.

Thanks,
Kurt

-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx [mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of Charles Wilt
Sent: Thursday, March 26, 2009 1:21 PM
To: Midrange Systems Technical Discussion
Subject: Re: To Key or Not To Key a Physical

Huh?

If you create a logical with the same access path as the physical, the
logical will share the PF access path.

Now-a-days, the recomendation is to always define a primary (aka
unique, non-NULL) key for the physical.

Charles

On Thu, Mar 26, 2009 at 2:13 PM, Kurt Anderson
<kurt.anderson@xxxxxxxxxxxxxx> wrote:

If I'm going to have multiple logical files over a physical file, is it better to not key the physical file or is there no implication if I do key the physical file (and reduce the number of logicals needed by 1)?

I'm not that familiar with how indexing works, and the concern is that a logical over a keyed physical will be indexing from an index.

Thoughts?

Thanks,

Kurt Anderson
Sr. Programmer/Analyst
CustomCall Data Systems
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