Re: Performance Difference Between != and <>?

  • From: "Jonathan Lewis" <jonathan@xxxxxxxxxxxxxxxxxx>
  • To: <oracle-l@xxxxxxxxxxxxx>
  • Date: Tue, 26 Sep 2006 21:04:52 +0100

I missed the original response to my post - so I've picked it up from here.

Is the phenomenon totally reproducible ?

Did you check the filter_predicates and access_predicates
of the plan, or just the structure. I don't expect any difference,
but a change in predicate order can result in a significant change
in CPU usage if you are unlucky.

If there is no difference there, then enable rowsource statistics
(alter session set "_rowsource_execution_statistics"=true) and
run the queries, then grab the execution plan from V$sql_plan
and join to v$sql_plan_statistics to see if any of the figures
about last_starts, last_XXX_buffer_gets, last_disk_reads,
last_elapsed_time give you a clue about where the time went.

If you are on 10gR2 there is a /*+ gather_plan_statistics */
hint you can use instead of the "alter session".


Jonathan Lewis

The Co-operative Oracle Users' FAQ

Cost Based Oracle: Fundamentals

----- Original Message ----- From: "Allen, Brandon" <Brandon.Allen@xxxxxxxxxxx>
To: <srcdco@xxxxxxx>; <oracle-l@xxxxxxxxxxxxx>
Sent: Monday, September 25, 2006 6:17 PM
Subject: RE: Performance Difference Between != and <>?


Have you tried going beyond just explain & autotrace and running a full
10046 level 12 trace to see where the slower version is spending its
time?  This might shed some light on the subject, plus - be sure to
verify that the explain plans are exactly the same in the 10046 trace
file (not the ones generated with the EXPLAIN= option), and in
v$sqlplan.  There are some "features" of autotrace and explain that can
cause it to not give you an accurate explain plan.


-----Original Message-----
   Thank you for your answer.  We did do an explain plan on
both versions of the statement and they were identical, which
is what is so puzzling about this.

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