RE: What else can cause different optimizer plan?

  • From: <paul.baumgartel@xxxxxxx>
  • To: <kerry.osborne@xxxxxxxxxxx>, <cshapi@xxxxxxxxx>, <oracle-l@xxxxxxxxxxxxx>
  • Date: Thu, 8 Dec 2011 16:13:13 -0500

Thanks for your replies.  A few observations in response to the points

 optimizer_env_hash_value is the same for both--does this not mean that
optimizer environments are identical?
 Underlying objects are the same (it's the same query issued by the same
 Query in pipelined function has one variable, which is passed in as
parameter.  Both sessions pass the same value.
 Plans displayed by dbms_xplan do not show use of cardinality feedback.
 No outlines, profiles, or baselines exist.
 No PX in either case.
 No histograms.

Paul Baumgartel
Group Finance Accounting Solutions
400 Atlantic Street
Stamford, CT 06904



-----Original Message-----
From: Kerry Osborne [mailto:kerry.osborne@xxxxxxxxxxx] 
Sent: Thursday, December 08, 2011 3:21 PM
To: cshapi@xxxxxxxxx
Cc: Baumgartel, Paul; oracle-l@xxxxxxxxxxxxx
Subject: Re: What else can cause different optimizer plan?

It's a long list. Here are a few more to come readily to mind.

Different optimizer environment (i.e. any of a whole bunch of parameters
is different)
Different underlying objects (your MYDATA table is not the same as Joe's
MYDATA table)
Data changes (range of value significantly exceeds what stats says it
Bind Variable Peeking kicks in
Cardinality Feedback feature kicks in
Adaptive Cursor Sharing kicks in
Someone creates an Outline, Profile, or Baseline on the statement
Size of memory structures (can determine whether a statement gets run
with PX plan or not)

The most common cause of plan instability is probably the combination of
histograms and bind variables (i.e. bind variable peeking).

Kerry Osborne

On Dec 8, 2011, at 2:04 PM, Gwen Shapira wrote:

> different statistics on objects, different system statistics or
> different bind variables.
> Gwen
> On Thu, Dec 8, 2011 at 10:39 AM,  <paul.baumgartel@xxxxxxx> wrote:
>> --
>> //
> --
> //

Visit our website at

This message contains confidential information and is intended only 
for the individual named.  If you are not the named addressee you 
should not disseminate, distribute or copy this e-mail.  Please 
notify the sender immediately by e-mail if you have received this 
e-mail by mistake and delete this e-mail from your system.
E-mails are not encrypted and cannot be guaranteed to be secure or 
error-free as information could be intercepted, corrupted, lost, 
destroyed, arrive late or incomplete, or contain viruses.  The sender 
therefore does not accept liability for any errors or omissions in the 
contents of this message which arise as a result of e-mail transmission.  
If verification is required please request a hard-copy version.  This 
message is provided for informational purposes and should not be 
construed as a solicitation or offer to buy or sell any securities 
or related financial instruments.

UBS reserves the right to retain all messages. Messages are protected
and accessed only in legally justified cases.

Other related posts: