CQE may time out and CQE startes searching through the indexes/DDS described
logical files beginning with the last logical file index created.
SQE presorts the logical files and indexes according the join criteria and
where clauses (and Group by and order By Conditions). The search ends, as
soon as an index is more expensive than the previous.
It would be interesting which query engine did the advice. I assume it was
the CQE which only works with estimated values and does not interrogate the
statistics.
Estimated values are not real values, that's why you may get an advice, but
created index is not used.
Mit freundlichen Grüßen / Best regards
Birgitta Hauser
"Shoot for the moon, even if you miss, you'll land among the stars." (Les
Brown)
"If you think education is expensive, try ignorance." (Derek Bok)
"What is worse than training your staff and losing them? Not training them
and keeping them!"
-----Ursprüngliche Nachricht-----
Von: midrange-l-bounces@xxxxxxxxxxxx
[mailto:midrange-l-bounces@xxxxxxxxxxxx] Im Auftrag von Charles Wilt
Gesendet: Monday, 14. September 2009 16:26
An: Midrange Systems Technical Discussion
Betreff: Re: Advised index not used but still advised
Rick,
Are there lots of indexes/logical files? The SQE may time out and not
look at every possible index.
Are there Select/Omit logicals? What's the QAQQINI setting for
IGNORE_DERIVED_INDEXES?
Charles
On Mon, Sep 14, 2009 at 10:17 AM, <Rick.Chevalier@xxxxxxxxxxxxxxx> wrote:
Last week I created seven indexes over one of our tables that were advised
by the index advisor. I got the information from system table SYSIXADV and
built the indexes with the key columns advised and installed them to
production Friday 9/12. Querying SYSIXADV this morning it shows a last
advised date of Saturday 9/13. I have compared the advised key columns and
they match exactly to the indexes I installed on Friday. The indexes were
created with SQL so the advisor should be happy about that.
I don't have access to the query because it originates outside of the
iSeries from our data warehouse group. The same query is run every night.
The index is requested for record selection. I know there is no guarantee
that the optimizer will use the index. I am wondering what would cause the
system to keep advising these indexes when they already exist?
Rick Chevalier
IT Software Solutions - Loan Servicing
[http://www.americredit.com/images/acf_email_sig.gif]
817-525-7178 (w)
rick.chevalier@xxxxxxxxxxxxxxx<mailto:rick.chevalier@xxxxxxxxxxxxxxx>
________________________________
Privileged and Confidential. This e-mail, and any attachments there to, is
intended only for use by the addressee(s) named herein and may contain
privileged or confidential information. If you have received this e-mail in
error, please notify me immediately by a return e-mail and delete this
e-mail. You are hereby notified that any dissemination, distribution or
copying of this e-mail and/or any attachments thereto, is strictly
prohibited.
--
This is the Midrange Systems Technical Discussion (MIDRANGE-L) mailing
list
To post a message email: MIDRANGE-L@xxxxxxxxxxxx
To subscribe, unsubscribe, or change list options,
visit: http://lists.midrange.com/mailman/listinfo/midrange-l
or email: MIDRANGE-L-request@xxxxxxxxxxxx
Before posting, please take a moment to review the archives
at http://archive.midrange.com/midrange-l.
midrange.com
