Re: Indexes vs Logical Files

It has never been true that having a Physical File (PF) with a key forced
the system to use CQE.

From the redbook, Preparing for and Tuning the SQL Query Engine on DB2 for

i5/OS, https://www.redbooks.ibm.com/redbooks/pdfs/sg246598.pdf

At its release in v5r2...

Dispatched to CQE if:
– >1 Table (that is, no joins)
– OR and IN predicates
– SMP requested
– Non-read (INSERT with subselect can use new path)
– LIKE predicates
– UNIONS
– View or logical file references
– Subquery
– Derived tables and common table expressions, UDTFs
– LOB columns
– LOWER, TRANSLATE, or UPPER scalar function
– CHARACTER_LENGTH, POSITION, or SUBSTRING scalar function using UTF-8/16
– Sort sequences and CCSID translation between columns
– Distributed queries via DB2 Multisystem
– Non-SQL queries (QQQQry API, Query/400, OPNQRYF)
– ALWCPYDTA(*NO) specified
– Sensitive cursor

In other words, given a PF, MYFILE, with a key column of MYKEY
select * from myfile where myKey = 'SOMEVALUE'

would use the SQE since its release.

Charles

On Fri, Oct 13, 2023 at 8:55 AM Jim Oberholtzer <midrangel@xxxxxxxxxxxxxxxxx>
wrote:

I believe at one time that was true. Since then the CQE has been
displaced by the SQE.

I would be looking at those logical files since they are most likely older
to see the page size (as some have suggested) and other attributes. Might
be worthy of a rebuild with newer parameters.



Jim Oberholtzer
Agile Technology Architects
Office: 414-433-4363
Mobile: 414-915-1445
Sent from mobile device

On Oct 13, 2023, at 9:19 AM, Gavin Inman <midrangelist@xxxxxxxxxxxxxx>

wrote:

IBM DB2 Engineer Mark Anderson was the one who told me this. If a

physical has keys, it is forced to COE.

On 10/13/2023 9:33 AM, Charles Wilt wrote:

That has never been the case.

And now-a-days, pretty much everything goes through the SQE.

Originally, if you referenced a LF on an SQL statement, you forced the

use

of the CQE.

Perhaps that's what you're thinking of. But again, even that is no

longer

the case.


Charles

On Fri, Oct 13, 2023 at 6:52 AM Gavin Inman<midrangelist@xxxxxxxxxxxxxx

wrote:

Years ago it was explained to me that if the physical has keys, it's
forced to use the older database engine. Unless something has changed,
I believe that's still true today.

Gavin.

On 10/13/2023 8:47 AM, Greg Wilburn wrote:

I've been using Index Advisor and Run Sql Scripts "Run and Explain" to
analyze some of our queries. I'm looking for increased performance.

I have a large file/table OEBOXCBX with a logical files defined with the
following keys:

LF #1: BXCOM#, BXORD#, BXREL#, BXBOX#, BXPRT#
LF #2: BXCOM#, BXORD#, BXREL#, BXBXNO, BXPRT#

I ran an SQL statement over a complex SQL view that contains this file.
RSS Run and Explain recommended the following index:
CREATE INDEX ASTHHOBJ/OEBOXCBX_IDX
ON ASTHHOBJ/OEBOXCBX (BXCOM# ASC, BXORD# ASC, BXREL# ASC) UNIT ANY
KEEP IN MEMORY NO;

My question is why the SQE wouldn't use one of the existing logical

files

as an index? As an RPG guy, this makes no sense to me.

TIA,
Greg

[Logo]<https://www.totalbizfulfillment.com/> Greg Wilburn
Director of IT
301.895.3792 ext. 1231
301.895.3895 direct
gwilburn@xxxxxxxxxxxxxxxxxxxxxxx<mailto:

gwilburn@xxxxxxxxxxxxxxxxxxxxxxx>

1 Corporate Dr
Grantsville, MD 21536
www.totalbizfulfillment.com<http://www.totalbizfulfillment.com>


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