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  3. March 2008

RE: Using the Index Advisor

True from the technology side. No so true from the multiple developer side and everyone knowing when, where and how to deal with an index with no DDS source and an LF. Recreating the LF gets the best use of the index and keeps everyone on the same page, just the database designer needs to know both worlds. At least during the transition phase to SQL while standards and rules are worked out and until retraining can happen

-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx [mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of MKirkpatrick@xxxxxxxxxxxxxxxxx
Sent: Wednesday, March 12, 2008 3:43 PM
To: Midrange Systems Technical Discussion
Subject: RE: Using the Index Advisor

or, I believe that you could just create the index and use that in your
HLL pgm. No need to create a LF.


midrange-l-bounces@xxxxxxxxxxxx wrote on 03/12/2008 12:30:56 PM:

So this might be one of those instances where I could consider
deleting the LF, creating the SQL index and then recreating the LF
so it shares the SQL index?

-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx [mailto:midrange-l-
bounces@xxxxxxxxxxxx] On Behalf Of Elvis Budimlic
Sent: Wednesday, March 12, 2008 3:21 PM
To: 'Midrange Systems Technical Discussion'
Subject: RE: Using the Index Advisor

Query optimizer is a funny animal. I don't think anyone can tell you
with
full certainty why it does some of the things it does.

I can tell you for sure it does "care" about keyed LFs!

One reason for redundant advice may be that having an SQL index with
larger
logical page size (64K vs LF's 8k) might bias query optimizer toward
using
that index. This is especially helpful in situations where index is
being
scanned sequentially (i.e. read-by-key, read-next-key, next....). Both
native I/O program can do this as well as query engine.

This is by no means the only "quirk" query optimizer has. I'm sure
you'll
run into more as you dig deeper into it.

HTH, Elvis

Celebrating 11-Years of SQL Performance Excellence on IBM i5/OS and
OS/400
www.centerfieldtechnology.com


-----Original Message-----
Subject: Using the Index Advisor

I was reviewing the Index Advisor in iSeries Navigator today and see
entries
advising me to create multiple indexes that I confirmed already exist
via a
logical file. The logical file has existed for years in some cases yet
the
advisor shows today as the last advised for query use date. Am I reading
this wrong or does the Index Advisor not care about DDS indexes?

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