Re: Optimizer Mode

  • From: "Jonathan Lewis" <jonathan@xxxxxxxxxxxxxxxxxx>
  • To: <si_g_palmer@xxxxxxxxx>, <oracle-l@xxxxxxxxxxxxx>
  • Date: Fri, 27 Jan 2012 20:21:33 -0000

Ignoring the details - the answer to your basic question is:
    You're not supposed to use first_rows - it's an outdated heuristically 
driven mechanism.
    If you want to make rationale tests and not confuse yourself you should 
use first_rows_N where N is one of the limited set of legal values 
including 10.
Your "all_rows" test actually ran as first_rows_10.


Regards

Jonathan Lewis
http://jonathanlewis.wordpress.com
Oracle Core (Apress 2011)
http://www.apress.com/9781430239543


----- Original Message ----- 
From: "Simon Palmer" <si_g_palmer@xxxxxxxxx>
To: <oracle-l@xxxxxxxxxxxxx>
Sent: Friday, January 27, 2012 4:10 PM
Subject: Optimizer Mode


Hello,
Just been doing some SPA work, just setting up and testing against some 
Swingbench SQLs. Did a trial of adjusting the optimizer_mode from ALL_ROWS 
to FIRST_ROWS.

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