RE: inefficient sql
- From: "Taylor, Chris David" <ChrisDavid.Taylor@xxxxxxxxxxxxxxx>
- To: "'Chris.Stephens@xxxxxxx'" <Chris.Stephens@xxxxxxx>, "'oracle-l@xxxxxxxxxxxxx'" <oracle-l@xxxxxxxxxxxxx>
- Date: Tue, 29 May 2012 15:28:16 -0500
Something to keep in mind is that many professionals (see Cary Millsap) make a
point of illustrating that only inefficient *and* business important SQL be
focused on (I'm overs simplifying a little bit). What I mean by this is,
suppose you have a query that runs once a week and uses gobs of LIOs. There
are lots of questions that you should ask yourself:
a.) is it impacting anyone (i.e. is anyone waiting on it)
b.) how many people are waiting on it
Now, some of that goes out the window if your whole system is swamped by a
bunch of little once a week SQLs... :)
I guess my only point in this is - don't focus on SQL tuning that isn't
impacting anyone.
(apologies to Cary if I misrepresented or overly simplified points made in the
past)
Chris Taylor
"Quality is never an accident; it is always the result of intelligent effort."
-- John Ruskin (English Writer 1819-1900)
Any views and/or opinions expressed herein are my own and do not necessarily
reflect the views of Ingram Industries, its affiliates, its subsidiaries or its
employees.
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On
Behalf Of Stephens, Chris
Sent: Tuesday, May 29, 2012 3:15 PM
To: 'oracle-l@xxxxxxxxxxxxx'
Subject: inefficient sql
I'm interested in creating a daily report to run in our development
environments to spot inefficient SQL early in the process.
I've already got one that lists top ten highest elapsed time and top ten most
frequently executed. They have helped tremendously in focusing on the right
SQL. However, there is often SQL here that makes its way into integration and
production that could be improved upon. (Yes I know where SQL falls in the
optimization hierarchy and am well aware that business tasks are what are
important but these reports have proved their value over and over.)
I'm pretty confident that a ratio of LIO's to rows returned by each row
operation in an SQL execution plan is a good indicator of SQL efficiency. I
think I've heard this in a few different presentations. I don't, however,
recall what that ratio should be or if I'm misremembering completely.
What do you all consider good indicators of inefficient SQL and how to you
identify those statements?
Thanks!
Chris
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