RE: What else can cause different optimizer plan?

From: Iotzov, Iordan <>
Date: Thu, 8 Dec 2011 16:58:54 -0500
Message-ID: <>

You can run event 10053 trace for each situation ( - it shows the calculations the CBO performs to get the execution plan. Look at the two trace files and see where they start to diverge. That may give you the clue about why the CBO generates different execution plan.

Iordan Iotzov

-----Original Message-----
From: [] On Behalf Of Sent: Thursday, December 08, 2011 4:13 PM To:;; Subject: RE: What else can cause different optimizer plan?

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

 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 user)
 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 [] Sent: Thursday, December 08, 2011 3:21 PM To:
Cc: Baumgartel, Paul; 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 is)
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, <> wrote:
>> --
> --

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Received on Thu Dec 08 2011 - 15:58:54 CST

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