RE: adaptive cursor sharing and bind peeking

  • From: Christian Antognini <Christian.Antognini@xxxxxxxxxxxx>
  • To: Mohamed Houri <mohamed.houri@xxxxxxxxx>
  • Date: Tue, 4 Jun 2013 06:35:44 +0000

Hi Mohamed

> May be I have not understood clearly the original poster question.
> For me the question was whether the CBO (for cursors that are bind aware)
> will always peek at the passed bind variable and optimize it or not?

The OP never asked whether a re-optimization was performed. Instead, he wanted 
to know whether bind peeking was taking place. So, the "and optimize it" part 
was added by you.

> This is why I answered that even if the cursor is bind aware the CBO will not
> always use the passed bind variable to optimize a new plan (child cursor).

This is true. Optimization is not done every time. But, bind peeking is done 
every time. 

> Instead it will share the plan that has been optimized for the bind variable 
> having the
> same "range of selectitivity" as the passed bind variable

To estimate the range of selectivity and select the best child cursor bind 
peeking must take place. 


In summary: To me it seems you are implying that "bind peeking" = 
"re-optimization". However, these are two completely different functionalities. 
Bind peeking might take place even though a re-optimization is not performed.


HTH
Chris Antognini

Troubleshooting Oracle Performance, Apress 2008
http://top.antognini.ch 


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