Thanks for the documentation, Charles. I'll flip through the redbook soon.
I was always somewhat frustrated with VE, because there was very little guidance as to WHY a particular access plan element was implemented in some undesirable way. Perhaps this will help me understand the tool better.
-Eric DeLong
-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx [mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of Charles Wilt
Sent: Wednesday, July 27, 2011 8:42 AM
To: Midrange Systems Technical Discussion
Subject: Re: sql not using existing indexes v6r1
VE is a much, much, better choice than the diag messages sent in debug mode.
http://www.redbooks.ibm.com/redbooks/pdfs/sg247326.pdf
- The debug messages are no longer being enhanced (that is, no new
messages are being
added for queries that go through SQE).
- No new messages are being added for queries that go through SQE,
for this reason the
SQE optimizer uses the closest CQE message and that message may or may not
accurately reflect the access plan built by the SQE optimizer.
- Important: Starting in V5R4, IBM is treating Debug Messages as a
non-strategic feedback
mechanism to analyze database Performance. There is no enhancement in V5R4.
http://www.mcpressonline.com/database/db2/get-your-system-humming-7-great-tips-for-tuning-db2-for-i.html
"After comparing just some of the differences between these two tools,
it should be abundantly clear that continued usage of the debug
messages for SQL performance analysis is ineffective and inefficient."
HTH,
Charles
On Tue, Jul 26, 2011 at 2:15 PM, DeLong, Eric <EDeLong@xxxxxxxxxxxxxxx> wrote:
Run it in debug to see better diagnostic messages...
Visual Explain should be able to generate a map of its access plan, which can be interesting and informative, but may not help you as much as you might think...
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